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2204
1241_05_2000_c1    © 2000, Cisco Systems, Inc.                  1




                  Introduction to Routing
                         Protocols
                                                 Session 2204


2204
1241_05_2000_c1    © 2000, Cisco Systems, Inc.                  2
Agenda



                  • IP, IPX Addressing Concepts
                  • Generic Routing Concepts
                  • Specific Routing Protocols
                  • Static and Defaults Routes


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1241_05_2000_c1    © 2000, Cisco Systems, Inc.                                                    3




                                                 MAC Address
                  48 Bit Hexadecimal (Base16) Unique Layer two address


                               1234.5678.9ABC
       First 24 bits = Manufacture Code                    Second 24 bits = Specific interface,
                assigned by IEEE                                assigned by Manufacture

      0000.0c XX.XXXX XXXX.XX00.0001
                                                  All F’s= Broadcast

                                           FFFF.FFFF.FFFF

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1241_05_2000_c1    © 2000, Cisco Systems, Inc.                                                    4
IP Addressing

                                                       32 Bits

                  Network                                         Host


                  8 Bits                         8 Bits          8 Bits         8 Bits




            172                       .           16        . 122 . 204

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1241_05_2000_c1    © 2000, Cisco Systems, Inc.                                               5




                                     IP Subnetting, Mask
                                                 Network                       Host

                IP
           Address                     172                 16             0            0
                                                 Network                       Host
            Default
            Subnet                     255                255             0            0
             Mask
                                                 Network              Subnet          Host
             8-bit
           Subnet                      255                255         255              0
            Mask



       Use Host Bits, Starting at the High Order Bit Position
2204
1241_05_2000_c1    © 2000, Cisco Systems, Inc.                                               6
IP Address Classes

                                                Start    1     0     0     0
             Class A:                            End    126   255   255   254
                                                Mask    255    0     0     0

                                                Start   128    0     0     0
              Class B:                           End    192   255   255   254
                                                Mask    255   255    0     0

                                                Start   192    0     0     0
              Class C:                           End    223   255   255   254
                                                Mask    255   255   255    0
     Class D: for multicast

2204
1241_05_2000_c1   © 2000, Cisco Systems, Inc.                                   7




                    IP Address Mask Formats

                    The Router will display different Mask
                          formats at different times.

  • bitcount ---172.16.31.6/24
  • decimal ---- 172.16.31.6 255.255.255.0
  • hexadecimal 172.16.31.6 0xFFFFFF00



2204
1241_05_2000_c1   © 2000, Cisco Systems, Inc.                                   8
Finding the IP Address
                                 on the LAN
   • ARP = Address Resolution                   UNIX Host A
     Protocol
   • Host and routers have pre
     assigned MAC addresses                     1111.1111.1111
                                                1111.1111.1111   5555.5555.5555
                                                                 5555.5555.5555

   • Host A sends a ARP request for
     router R1
                                                2222.2222.2222
                                                2222.2222.2222
   • The ARP request is a broadcast
     packet                                         R1     3333.3333.3333
                                                           3333.3333.3333

   • R1 replies with ARP response
     unicast address                                          4444.4444.4444
                                                              4444.4444.4444

   • Now both Host A and Router R1                                   R2
     have the IP and MAC address for
     each other in their ARP Table
2204
1241_05_2000_c1   © 2000, Cisco Systems, Inc.                                  9




              How Do I Get there From Here?
     UNIX Host                                                   UNIX Host




     Street A                                                    Street H




           • Path choice is based on location
           • Location is represented by an address
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1241_05_2000_c1   © 2000, Cisco Systems, Inc.                                  10
Host Addresses


        172. 16. 200.11                                                10.1.1.1/8
        255.255. 0. 0                           E0        E1

           172. 16.3.10                                                10.250.8.11
           255.255.0.0                                                 255. 0. 0. 0

      172.16.12.12/16                                                  10.180.30.118/8

                  IP: 172.16.2.1/16                            IP: 10.6.24.2/8

                                                                 Forwarding Table
        172 .16              12 . 12
                                                                 Network    Interface
        255.255                    0.0                          172.16.0.0      E0
       Network                    Host                            10.0.0.0       E1
2204
1241_05_2000_c1   © 2000, Cisco Systems, Inc.                                            11




                                    Subnet Addressing


                                                                        172.16. 3 . 5
        172.16.2.11/24
                                                E0        E1            255.255.255.0

       172. 16. 2 . 2
                                                                       172.16.3.100/24
       255.255.255.0


  172.16.2.160/24                                                      172.16.3.150/24

                  IP: 172.16.2.1/24                            IP: 172.16.3.1/24

                                                                 Forwarding Table
                                                                 Network    Interface
       172 .16                         2         160
                                                                172.16.2.0      E0
        255.255                    .255              .0
      Network                  Subnet            Host           172.16.3.0       E1
2204
1241_05_2000_c1   © 2000, Cisco Systems, Inc.                                            12
Discontiguous IP Subnet

                                                                          A
        Where Is                                                                      172.16.50.1
                                                                                      172
       172.16.0.0?                                                                    255.255.255.0
                                                     192.168.1.4     .5
                                                 255.255.255.252              .13

                                             B
                                                    .6
      172.16.40.1
      172.16
    255.255.255.0                                                               192.168.1.12
                                                                                255.255.255.252
                                                    .9

                                                     192.168.1.8          .14
                                                 255.255.255.252    .10               172.16.60.1
                                                                                      255.255.255.0
Routing Protocols will by Default
  Summarize Major Networks                                                C


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1241_05_2000_c1    © 2000, Cisco Systems, Inc.                                                        13




                  Variable Length Subnet Mask

                                                                          A
                                                                                      172.16.50.1
                                                                     .5               255.255.255.0
                                                       172.16.1.4
                                                 255.255.255.252              .13

                                             B
                                                    .6
      172.16.40.1
    255.255.255.0                                                               172.16.1.12
                                                                                255.255.255.252
                                                    .9

  172.16.1.X With a                                    172.16.1.8         .14
255.255.255.252 mask                             255.255.255.252    .10               172.16.60.1
 Or /30 the 1 subnet                                                                  255.255.255.0
my be broken into 64
        Subnets                                                           C
                                 Conserve IP Addresses
2204
1241_05_2000_c1    © 2000, Cisco Systems, Inc.                                                        14
IPX Addressing

                                                       80 Bits

                       Network                                   Node


                           32 Bits                               48 Bits




           000C 15C0                                     0077.0650.2328
                  IPX Network #                                IPX STATION #
                                                         Usulay same a MAC address

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1241_05_2000_c1     © 2000, Cisco Systems, Inc.                                      15




                             Address Configuration

            Router (config-if) #
              ip address ip-address subnet-mask

                  • Assigns an address and subnet mask
                  • Starts IP processing on an interface

              ipx network network

                  • Assigns a network number
                  • Starts IPX processing on an interface
                  • Must have ipx routing configured
2204
1241_05_2000_c1     © 2000, Cisco Systems, Inc.                                      16
Agenda



                      • IP, IPX Addressing Concepts
                      • Generic Routing Concepts
                      • Specific Routing Protocols
                      • Static and Defaults Routes


2204
1241_05_2000_c1         © 2000, Cisco Systems, Inc.                                                     17




                                                       Convergence

      • Time required for router to identify and
        use an alternate path
      • Dependent on timer values and algorithm
      • Difficult to predict precisely

         A,B,C                         A,B,C                            B,C
         D,E,F                         D,E,F                            D,E,F
                  2                             4                  6
                                                                                   Router’s 5 and 6
                               C                              E    F
                  B                             D                               Have no knowledge of
     A                                                                          the new Network A Yet
                  1                              3 A,B,C           5
                      A,B,C                                            B,C
                      D,E,F                           D,E,F            D,E,F

2204
1241_05_2000_c1         © 2000, Cisco Systems, Inc.                                                     18
Load Balancing


                                                       T1          T1
                                                              R2

                  N1                                                               N2

                                              R1                         R4

                                                       T1     R3    T1



                                              • Equal cost paths
                                              • Rapid failover
2204
1241_05_2000_c1        © 2000, Cisco Systems, Inc.                                      19




                                                     Load Balancing


                                                     256K          768K
                                                              R2

                   N1                                                         N2

                                              R1            512K         R4
                                                              R3    T1




        • Unequal cost load balancing: Eigrp

2204
1241_05_2000_c1        © 2000, Cisco Systems, Inc.                                      20
Holddown

                   I Will Ignore
                   Routes to X
                     While in
                    Holddown
                                                            x

                  • Sets minimum convergence time
                  • Prevents forwarding loops
2204
1241_05_2000_c1    © 2000, Cisco Systems, Inc.                  21




                           Forwarding Loop:
                        A Routing Disagreement



      Packets for Network X




         • Packets do not get to the destination
         • Temporary traffic surge until convergence

2204
1241_05_2000_c1    © 2000, Cisco Systems, Inc.                  22
Split Horizon


  “
        Do not send routing data
        back in the direction from
              which it came

                                                                                     ”
2204
1241_05_2000_c1       © 2000, Cisco Systems, Inc.                                        23




                                                    Split Horizon

                  Frame Relay Multipoint Network
          Router 2,3,4
 All advertise their Respective
Ethernets to Router D, Router D
       knows all networks
                                                             PVC
                                                                         2       A

                                                                A

                                                                   PVC
  D               1                                                          3       B
                                                                         B
                                S0
                                                           PVC C
                                                                         4       C


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1241_05_2000_c1       © 2000, Cisco Systems, Inc.                                        24
Split Horizon

                                      Frame Relay Network
         Router 1
   Advertises network D
     to routers 2,3,4                                                   2       A
                                                            PVC


                                                                  PVC
  D               1                                                         3       B
                                S0
                                                           PVC

             Router 1                                                   4       C
    Knows all networks but
 Will only advertise D out of S0
Because it learned A,B,C from S0
2204
1241_05_2000_c1       © 2000, Cisco Systems, Inc.                                       25




                                                    Metrics (Cost)

      • Numeric value used to choose
        among paths
      • RIP/RIPv2 is hop count and ticks (IPX)
      • OSPF/ISIS is interface cost (bandwidth)
      • (E)IGRP is compound
      • BGP can be complicated
      • Path determination depends on metric
2204
1241_05_2000_c1       © 2000, Cisco Systems, Inc.                                       26
Agenda



                  • IP, IPX Addressing Concepts
                  • Generic Routing Categories
                  • Specific Routing Protocols
                  • Static and Defaults Routes


2204
1241_05_2000_c1    © 2000, Cisco Systems, Inc.                                               27




                                         Forwarding Table

         One Forwarding Table per Router
    One Forwarding Table per Network Protocol

      Network #               Interface          Next Hop    Metric       Age       Source

   198.113.181.0 Ethernet0 192.150.42.177 [170/304793] 02:03:50                       D

   198.113.178.0 Ethernet0 192.150.42.177                   [110/9936]   02:03:50     O

    192.168.96.0             Ethernet0 192.150.42.177        [120/3]     00:00:20     R

    192.168.97.0             Ethernet0                                                C




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1241_05_2000_c1    © 2000, Cisco Systems, Inc.                                               28
Building the Forwarding Table




                  • Directly connected
                        Routes that the router is attached to

                  • Static
                        Routes are manually defined

                  • Dynamic
                        Routes protocol are learned from a Protocol
2204
1241_05_2000_c1     © 2000, Cisco Systems, Inc.                                         29




                                         Routing Protocols

                   I Know About:                                    I Know About:
                     Network A                                        Network X
                     Network B                                        Network Y
       A             Network C                     Routing Update      Network Z    X
       B                                                                            Y
       C                                     Exchanges Network Knowledge            Z



• Routing protocol updates are exchanged by routers
  to learn about paths to other logical networks
• Each routing protocol offers features that can make
  it desirable as part of an internetwork design

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1241_05_2000_c1     © 2000, Cisco Systems, Inc.                                         30
Routing Protocol Goals

   • Optimal path selection                        • Easy to configure
   • Loop-free routing                             • Adapts to changes
                                                     easily and quickly
   • Fast convergence
                                                   • Does not create a lot
   • Limited design
                                                     of traffic
     administration
                                                   • Scales to a large size
   • Minimize update traffic
                                                   • Compatible with existing
   • Handle address limitations
                                                     hosts and routers
   • Support hierarchical
                                                   • Supports variable length
     topology
                                                     subnet masks and
   • Incorporate rapid                               discontiguous subnets
     convergence
                                                   • Supports policy routing
2204
1241_05_2000_c1   © 2000, Cisco Systems, Inc.                                   31




                                                IP RIP

• Routing Information                               • RFC 1058
  Protocol
                                                    • Simple = limited
• Widely available
                                                    • Slow convergence
• Hop count metric
                                                    • No VLSM
• Periodic update
                                                    • No discontiguous
• Easy to implement                                   subnets
• One of the first                                  • Max 15 Hops
  available
2204
1241_05_2000_c1   © 2000, Cisco Systems, Inc.                                   32
RIP—Distance Vector

  Net A                                                                               Net D
                      R1                                R2                      R3
                                         Net B                     Net C
            E0                         S0      S0             S1           S0        E0



           Network Interface                     Network Interface     Network Interface
              A       E0                            B       S0            C       S0
              B       S0                            C       S1            D       E0
              C       S0                            A       S0            B       S0
              D       S0                            D       S1            A       S0


       Send RIP Routing Table to Neighbors
2204
1241_05_2000_c1    © 2000, Cisco Systems, Inc.                                                33




                  Broadcast Routing Updates

                  All Stations Have to Listen to Rip Broadcast’s




                                  S 10.1.1.1 D 255.255.255.255


                                                    RIP V1


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1241_05_2000_c1    © 2000, Cisco Systems, Inc.                                                34
RIP Metric


                                                      1 Hop
                                                                    Hops
                                  Path A
                                                       R2



                                                T1             T1

                                                       56k
                   R1                                                  R3



                                     Path B
                                                      0 Hops

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1241_05_2000_c1   © 2000, Cisco Systems, Inc.                               35




                                                     RIP V2

          • RFC 1723
          • Cisco IOS® 11.1 support
          • Advertises masks
          • Variable length subnet masks
          • Route summarization
          • Routing updates use multicast
          • Authenticated updates using MD5
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1241_05_2000_c1   © 2000, Cisco Systems, Inc.                               36
Multicast Routing Updates




                                                RIP V2


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1241_05_2000_c1   © 2000, Cisco Systems, Inc.            37




                                    When to Use RIPv2




                     • Subnet mask support
                     • Reduce broadcast load
                     • Validated updates
                     • Multivendor environment

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1241_05_2000_c1   © 2000, Cisco Systems, Inc.            38
IPX RIP

   • Widely available                                  • Tied to SAP
                                                         protocol
   • Hop count metric
                                                       • Simple = limited
   • Ticks (1/18 sec)
                                                       • Slow convergence
   • Periodic update
                                                       • No default route
   • Easy to implement
                                                       • Routing loops
   • Free on servers
                                                       • Max 15 hops

2204
1241_05_2000_c1   © 2000, Cisco Systems, Inc.                               39




                                                IPX RIP—Ticks


   • Ticks are used                                    • IPXWAN
     to determine                                        calculates for
     server timeout                                      its interfaces
   • Default for LAN                                   • can be set via
     interfaces is 1                                     the ipx delay
                                                         number interface
   • Default for WAN
                                                         sub command
     interfaces is 4

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1241_05_2000_c1   © 2000, Cisco Systems, Inc.                               40
IGRP


   • Interior Gateway •                                   Cisco IOS 9.21
     Routing Protocol
                      •                                   Periodic update
   • Cisco developed
                      •                                   No VLSM
   • Distance vector
                      •                                   Default timers
   • Compound                                             produce slow
     metric                                               convergence

2204
1241_05_2000_c1   © 2000, Cisco Systems, Inc.                                 41




                         IGRP Compound Metric

           • Administrative
             weight                                                      T1
                                                            R2
           • Delay
           • Bandwidth                               T1

           • Reliability                                    56k

           • Load                               R1                  R3


                   (K2 * BW)                           K5
     = ((K1 * BW + (256-load) + K3* delay)) * (reliability + K ))
                                                              4
2204
1241_05_2000_c1   © 2000, Cisco Systems, Inc.                                 42
How the IGRP Metrics Work

 Delay Metric-                                  D1       D2          D3
    Based on
 D1 + D2 + D3



   Bandwidth                              1.5 Mbps     64 kbps     1.5 Mbps
 Metric-Based
  on 64 kbps

           • Bandwidth dominates short paths
           • Delay dominates long paths
           • Configure bandwidth on all interfaces
2204
1241_05_2000_c1   © 2000, Cisco Systems, Inc.                                   43




                                                Enhanced IGRP

   • Extremely fast                                   • Best of DV and LS
     convergence
                                                      • Low overhead
   • VLSM support
                                                      • Guaranteed
   • Discontiguous                                      loop-free
     subnets
                                                      • Reliable, incremental
   • Arbitrary route                                    update-based
     summarization
                                                      • Multiprotocol:
   • Supports prefix and                                IP, IPX®, AppleTalk
     host routing
                                                      • Easy to configure
2204
1241_05_2000_c1   © 2000, Cisco Systems, Inc.                                   44
Advanced Distance Vector
                                                                       On Startup Routing Tables
                                                                        Are Exchanged; Routing
                                                          A   27
                                                                       Table Built Based on Best
                                                          B   12       Paths from Topology Table
         A         1                                 Z    C   35
         B        13
         C        20
                                                                                 A    27   Z
                                                              A    Q   2              1    Q
                                                              B    Z   13
             Q                                       Y                                5    X
                                                              C    X   13        B    12   Z
                                                                                 ..   ..   ..
                                                              Y’s Table
                  A        5                                                   Topology Table
                  B        3
                  C        3                         X   • Construct neighbor tables
             X’s Table
                                                         • Construct topology tables
                                                         • Compute routes
2204
1241_05_2000_c1        © 2000, Cisco Systems, Inc.                                                 45




                                                     EIGRP Tables

  • Topology table                                                 • Neighbor table
  • Acted upon by DUAL • Keeps adjacent
                            neighbor’s address
  • All routes advertised
    by neighbors          • Keeps the hold time
  • List of neighbors for                                          • Information for
    each route                                                       reliable transport
  • Routes passive
    or active
2204
1241_05_2000_c1        © 2000, Cisco Systems, Inc.                                                 46
Diffusing Update
                                         Algorithm (DUAL)

       • DUAL is a loop-free routing algorithm
         that performs a diffused computation
         of a routing table
                  Uses a new routing algorithm
                  Achieves fast convergence
                  Network changes propagate only to affected
                  nodes (“bounded updates”)
       • No need for route holddown

2204
1241_05_2000_c1    © 2000, Cisco Systems, Inc.                 47




                                                 IPX EIGRP


        • Automatic redistribution of routes
          into RIP/SAP
        • Maximum network size is 224 hops
          vs 15 for RIP
        • Incremental SAPs sent, reducing
          bandwidth usage
        • All other benefits of EIGRP
2204
1241_05_2000_c1    © 2000, Cisco Systems, Inc.                 48
When to Use EIGRP



                  • Very large, complex networks
                  • VLSM
                  • For fast convergence
                  • Little network design
                  • Multiprotocol support

2204
1241_05_2000_c1    © 2000, Cisco Systems, Inc.                                                      49




                                       Link State Routing

                                                     Z’s Link State
 Q’s Link State
                                                                         Topology Information Is
                                                 Z                    Kept in a Database Separate
                                                                       from the Forwarding Table

                                                            A   Q     2
                                                            B   Z     13
             Q                                   Y          C   X     13


                                                                                  • OSPF
                                                 X
       X’s Link State                                                             • IS-IS
                                                                                  • NLSP
2204
1241_05_2000_c1    © 2000, Cisco Systems, Inc.                                                      50
Link State Routing

          • Neighbor discovery
          • Constructing an LSA (Link State
            Advertisement)
          • Distribute LSA
          • Compute routes using SPF
            (Shortest Path First)
          • On network failure
                  New LSAs flooded
                  All routers recompute link state databases
2204
1241_05_2000_c1   © 2000, Cisco Systems, Inc.                              51




                                                OSPF

   • Open Shortest                                • Fast convergence
     Path First
                                                  • Variable-length
   • Link state or SPF                              subnet masks
     technology
                                                  • Discontiguous
   • Developed by OSPF                              subnets
     working group of
                                                  • No periodic updates
     IETF (RFC 1253)
                                                  • Route authentication
   • Designed expressly
     for TCP/IP Internet                          • Delivered two years
     environment                                    after IGRP
2204
1241_05_2000_c1   © 2000, Cisco Systems, Inc.                              52
OSPF Areas and Rules
                                                                              Area
• Backbone area (0)                                                          Border
                                                                             Router
  must be present
• All other areas                                          Area 2                          Area 3
  must have
                                                                             Area 0            Internal
  connection                                    Backbone
                                                                                                Router
  to backbone                                    Router

• Backbone must                                                     Area 4
  be contiguous                                                                       Area 1

• Do not partition
  area (0)                                                                     Autonomous
                                                Internet
                                                                                System (AS)
                                                                               Border Router
2204
1241_05_2000_c1   © 2000, Cisco Systems, Inc.                                                             53




                                     When to Use OSPF

                  • Large hierarchical networks
                  • Complex networks, except…
                          Topology restrictive
                          Additional network design
                  • VLSM
                  • Fast convergence
                  • Multivendor
2204
1241_05_2000_c1   © 2000, Cisco Systems, Inc.                                                             54
IS-IS

   • IS = Intermediate                             • ISO 10589
     System
                                                   • Two types of areas:
   • Dual IS-IS                                         Level-1 other areas
   • Integrated IS-IS                                   Level-2 backbone
   • Metric is 10 bits                             • Default for
     wide                                            each level
   • All interfaces                                • Much like OSPF
     default to 10
2204
1241_05_2000_c1   © 2000, Cisco Systems, Inc.                                 55




             NetWare Link Services Protocol


             • Derived from ISIS
             • NLSP specs 3 levels of routers
             • Only two levels are defined
             • Spec is Novell NLSP version 1.1
                    http://www.novell.com
                    http://developer.novell.com/research

2204
1241_05_2000_c1   © 2000, Cisco Systems, Inc.                                 56
BGP

   • RFC 1771                                              • Many options for
                                                             policy enforcement
   • Border Gateway
     Protocol             • Classless Inter
                            Domain Routing
   • Version 4 is current
                            (CIDR)
   • Exterior routing
                          • Widely used for
     protocol (vs.
                            Internet backbone
     interior)
                          • AS=Autonomous
   • Uses TCP for           systems
     transport
2204
1241_05_2000_c1    © 2000, Cisco Systems, Inc.                                    57




                                                     BGP Basics

                                                       Peering

                                                 A                   C
                  AS 100                                                 AS 101
                                                 B                   D


                                                                 E
    • Runs over TCP                                         AS 102
    • Path vector
      protocol
    • Incremental update
2204
1241_05_2000_c1    © 2000, Cisco Systems, Inc.                                    58
Internal BGP (IBGP) Peering

                                                        AS 100
                                                                     D
                                                A
                                                         B




                                                             E



                  •     BGP peer within the same AS
                  •     Not required to be directly connected
                  •     IBGP neighbors should be fully meshed
                  •     Few BGP speakers in corporate network
2204
1241_05_2000_c1       © 2000, Cisco Systems, Inc.                                 59




                  External BGP (EBGP) Peering


                                                    A
                      AS 100                                             AS 101
                                                                 C

                                                    B



          • Between BGP speakers in different AS
          • Should be directly connected
          • Don’t run an IGP between EBGP peers

2204
1241_05_2000_c1       © 2000, Cisco Systems, Inc.                                 60
Policy Drives
                                       BGP Requirements

                                                        AS 200           Static
                                                                         Route
                                      BGP

                  AS 100                                         BGP              AS 400

                                           BGP
                                                        AS 300




           • Policy for AS 100: Always use AS 300
             path to reach AS 400

2204
1241_05_2000_c1      © 2000, Cisco Systems, Inc.                                            61




                                When Not to Use BGP
                                                                                  Network
                                                   Static                         Number
                                                                           C
                                           A                     ISP Runs BGP
                                                            B
                                                            B


                  Advertise Default
                  Network Via IGP Use a Static Route to
                                    Provide Connectivity


              • Avoid BGP configuration by using
                default networks and static routes
                      Appropriate when the local policy is the
                      same as the ISP policy
2204
1241_05_2000_c1      © 2000, Cisco Systems, Inc.                                            62
Agenda



                  • IP, IPX Addressing Concepts
                  • Generic Routing Categories
                  • Specific Routing Protocols
                  • Static and Defaults Routes


2204
1241_05_2000_c1    © 2000, Cisco Systems, Inc.                   63




                                                 Static Routes



            • Routes configured manually
            • Useful when few or just one
              route exist
            • Can be administrative burden
            • Frequently used for default route

2204
1241_05_2000_c1    © 2000, Cisco Systems, Inc.                   64
Administrative Distance
     • The router treats different routing protocols with a different preference
                      Route Source                                Default Distance
                      Connected Interface                                0
                      Static Route                                       1
                      Enhanced IGRP Summary Route                        5
                      External BGP                                      20
                      Internal Enhanced IGRP                            90
                      IGRP                                              100
                      OSPF                                              110
                      IS-IS                                             115
                      RIP                                               120
                      EGP                                               140
                      External Enhanced IGRP                            170
                      Internal BGP                                      200
                      Unknown, Discard Route                            255
2204
1241_05_2000_c1     © 2000, Cisco Systems, Inc.                                            65




                               Floating Static Routes

                  • A static route with a high distance
                  • Can be overridden by dynamic info

                                                         T1

                         172.16.3.2
                             3                                                172.16.1.0
                                                  ISDN
                                                                               C15C0
                                                     172.16.3.1
                                                         3
      ip route 172.16.1.0 255.255.255.0 172.16.3.1 140

      ipx route C15C0 3.0000.0c15.3628 floating-static
2204
1241_05_2000_c1     © 2000, Cisco Systems, Inc.                                            66
Default Routes

              • Route used if no match is found in
                forwarding table
              • Can be carried by routing protocols
              • Two models
                      Special network number:
                             0.0.0.0 (IP)
                             -2 (IPX)
                      Flagged in routing protocol
              • Protocols support multiple models
2204
1241_05_2000_c1   © 2000, Cisco Systems, Inc.                    67




                       Creating a Default Route



     • RIP, RIPv2: network 0.0.0.0
     • IGRP, EIGRP: ip default-network
     • OSPF:ISIS default originate
     • IPX: ipx route default
     • default gateway is for “host mode”

2204
1241_05_2000_c1   © 2000, Cisco Systems, Inc.                    68
Default IP Subnet

            172.16.0.0                                                              Internet
                                                        s0        s1




                                                        172.16.1.0

                  • Two defaults
                               For unknown networks
                               For unknown subnets

                  • Controlled by ip classless
2204
1241_05_2000_c1   © 2000, Cisco Systems, Inc.                                                      69




          Comparison of Routing Protocols


                                                Link         Traditional   Advanced       Path
                                                State         Distance     Distance      Vector
                                                               Vector       Vector

   Scalability                                  Good            Low        Excellent   Outstanding
   Bandwidth                                    Low             High         Low           Low

   Memory                                       High            Low        Moderate       High
   CPU                                          High            Low          Low        Moderate

   Convergence                                  Fast            Slow         Fast       Moderate
   Configuration                        Moderate                Easy        Easy          Hard


2204
1241_05_2000_c1   © 2000, Cisco Systems, Inc.                                                      70
Internet Routing Protocols


       • IP routing protocols are characterized as

 Name              Type            Proprietary Function Updates Metric        VLSM   Summ

 RIP                DV                        No   Interior   30 Sec   Hops    No    Auto
 RIPv2              DV                        No   Interior   30 Sec   Hops   Yes    Auto
 IGRP               DV                      Yes    Interior   90 Sec   Comp    No    Auto
 EIGRP            Adv DV                    Yes    Interior   Trig     Comp   Yes    Both
 OSPF               LS                        No   Interior   Trig     Cost   Yes    Man
 IS-IS              LS                        No   Interior   Trig     Cost   Yes    Auto
 BGP              Path Vec                    No   Exterior    Incr    N/A    Yes    Auto

2204
1241_05_2000_c1      © 2000, Cisco Systems, Inc.                                            71




                                 Topology/Technology
                                    Considerations
          • Routing and services overhead is usually
            not a big deal when you have a lot of
            bandwidth (i.e. LANs)
          • Protect WAN bandwidth using update-based
            protocols—more bandwidth and buffers for
            application traffic
          • High densities of sub (interfaces) can cause
            “hot spots” and router CPU overload
          • NBMA (Non-Broadcast Multi-Access)
            technologies always require good
            design practices
2204
1241_05_2000_c1      © 2000, Cisco Systems, Inc.                                            72
For Further Reference…

             • EIGRP Network Design Solutions
               by Ivan Pepelnjak,(ISBN: 1578701651)
             • Interconnections : Bridges and Routers
               by Radia Perlman (ISBN: 0-20156-332-0)
             • Internetworking with TCP / IP, Volume 1:
               Principles, Protocols, and Architecture
               by Douglas Comer (ISBN: 0-13216-987-8)
             • IP Routing Fundamentals
               by Mark Sportack (ISBN: 1-57870-071-x)
             • IP Routing Primer
               by Robert Wright (ISBN: 1-57870-108-2)
             • OSPF Network Design Solutions
               by Thomas, Thomas M. (ISBN: 1-57870-046-9)
2204
1241_05_2000_c1   © 2000, Cisco Systems, Inc.                   73




                        For Further Reference…


              • Routing in the Internet
                by Christian Huitema (ISBN: 0-13132-192-7)
              • OSPF Network Design Solutions
                by Thomas, Thomas M. (ISBN: 1-57870-046-9)
              • ISP Survival Guide : Strategies for Running a
                Competitive ISP
                by Geoff Huston (ISBN:0-47131-499-4)
              • Internet Routing Architectures
                by Bassam Halabi (ISBN: 1-56205-652-2)



2204
1241_05_2000_c1   © 2000, Cisco Systems, Inc.                   74
Thank You!



                   • Related sessions:
                                2208 Deploying IGRP/EIGRP
                                2205 Deploying OSPF
                                2209 Deploying BGP
                                2200 Advanced IP Routing

2204
1241_05_2000_c1    © 2000, Cisco Systems, Inc.                  75




                  Introduction to Routing
                         Protocols
                                                 Session 2204


2204
1241_05_2000_c1    © 2000, Cisco Systems, Inc.                  76
Please Complete Your
                     Evaluation Form
                                                Session 2204


2204
1241_05_2000_c1   © 2000, Cisco Systems, Inc.                  77




2204
1241_05_2000_c1   © 2000, Cisco Systems, Inc.                  78

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2204

  • 1. 2204 1241_05_2000_c1 © 2000, Cisco Systems, Inc. 1 Introduction to Routing Protocols Session 2204 2204 1241_05_2000_c1 © 2000, Cisco Systems, Inc. 2
  • 2. Agenda • IP, IPX Addressing Concepts • Generic Routing Concepts • Specific Routing Protocols • Static and Defaults Routes 2204 1241_05_2000_c1 © 2000, Cisco Systems, Inc. 3 MAC Address 48 Bit Hexadecimal (Base16) Unique Layer two address 1234.5678.9ABC First 24 bits = Manufacture Code Second 24 bits = Specific interface, assigned by IEEE assigned by Manufacture 0000.0c XX.XXXX XXXX.XX00.0001 All F’s= Broadcast FFFF.FFFF.FFFF 2204 1241_05_2000_c1 © 2000, Cisco Systems, Inc. 4
  • 3. IP Addressing 32 Bits Network Host 8 Bits 8 Bits 8 Bits 8 Bits 172 . 16 . 122 . 204 2204 1241_05_2000_c1 © 2000, Cisco Systems, Inc. 5 IP Subnetting, Mask Network Host IP Address 172 16 0 0 Network Host Default Subnet 255 255 0 0 Mask Network Subnet Host 8-bit Subnet 255 255 255 0 Mask Use Host Bits, Starting at the High Order Bit Position 2204 1241_05_2000_c1 © 2000, Cisco Systems, Inc. 6
  • 4. IP Address Classes Start 1 0 0 0 Class A: End 126 255 255 254 Mask 255 0 0 0 Start 128 0 0 0 Class B: End 192 255 255 254 Mask 255 255 0 0 Start 192 0 0 0 Class C: End 223 255 255 254 Mask 255 255 255 0 Class D: for multicast 2204 1241_05_2000_c1 © 2000, Cisco Systems, Inc. 7 IP Address Mask Formats The Router will display different Mask formats at different times. • bitcount ---172.16.31.6/24 • decimal ---- 172.16.31.6 255.255.255.0 • hexadecimal 172.16.31.6 0xFFFFFF00 2204 1241_05_2000_c1 © 2000, Cisco Systems, Inc. 8
  • 5. Finding the IP Address on the LAN • ARP = Address Resolution UNIX Host A Protocol • Host and routers have pre assigned MAC addresses 1111.1111.1111 1111.1111.1111 5555.5555.5555 5555.5555.5555 • Host A sends a ARP request for router R1 2222.2222.2222 2222.2222.2222 • The ARP request is a broadcast packet R1 3333.3333.3333 3333.3333.3333 • R1 replies with ARP response unicast address 4444.4444.4444 4444.4444.4444 • Now both Host A and Router R1 R2 have the IP and MAC address for each other in their ARP Table 2204 1241_05_2000_c1 © 2000, Cisco Systems, Inc. 9 How Do I Get there From Here? UNIX Host UNIX Host Street A Street H • Path choice is based on location • Location is represented by an address 2204 1241_05_2000_c1 © 2000, Cisco Systems, Inc. 10
  • 6. Host Addresses 172. 16. 200.11 10.1.1.1/8 255.255. 0. 0 E0 E1 172. 16.3.10 10.250.8.11 255.255.0.0 255. 0. 0. 0 172.16.12.12/16 10.180.30.118/8 IP: 172.16.2.1/16 IP: 10.6.24.2/8 Forwarding Table 172 .16 12 . 12 Network Interface 255.255 0.0 172.16.0.0 E0 Network Host 10.0.0.0 E1 2204 1241_05_2000_c1 © 2000, Cisco Systems, Inc. 11 Subnet Addressing 172.16. 3 . 5 172.16.2.11/24 E0 E1 255.255.255.0 172. 16. 2 . 2 172.16.3.100/24 255.255.255.0 172.16.2.160/24 172.16.3.150/24 IP: 172.16.2.1/24 IP: 172.16.3.1/24 Forwarding Table Network Interface 172 .16 2 160 172.16.2.0 E0 255.255 .255 .0 Network Subnet Host 172.16.3.0 E1 2204 1241_05_2000_c1 © 2000, Cisco Systems, Inc. 12
  • 7. Discontiguous IP Subnet A Where Is 172.16.50.1 172 172.16.0.0? 255.255.255.0 192.168.1.4 .5 255.255.255.252 .13 B .6 172.16.40.1 172.16 255.255.255.0 192.168.1.12 255.255.255.252 .9 192.168.1.8 .14 255.255.255.252 .10 172.16.60.1 255.255.255.0 Routing Protocols will by Default Summarize Major Networks C 2204 1241_05_2000_c1 © 2000, Cisco Systems, Inc. 13 Variable Length Subnet Mask A 172.16.50.1 .5 255.255.255.0 172.16.1.4 255.255.255.252 .13 B .6 172.16.40.1 255.255.255.0 172.16.1.12 255.255.255.252 .9 172.16.1.X With a 172.16.1.8 .14 255.255.255.252 mask 255.255.255.252 .10 172.16.60.1 Or /30 the 1 subnet 255.255.255.0 my be broken into 64 Subnets C Conserve IP Addresses 2204 1241_05_2000_c1 © 2000, Cisco Systems, Inc. 14
  • 8. IPX Addressing 80 Bits Network Node 32 Bits 48 Bits 000C 15C0 0077.0650.2328 IPX Network # IPX STATION # Usulay same a MAC address 2204 1241_05_2000_c1 © 2000, Cisco Systems, Inc. 15 Address Configuration Router (config-if) # ip address ip-address subnet-mask • Assigns an address and subnet mask • Starts IP processing on an interface ipx network network • Assigns a network number • Starts IPX processing on an interface • Must have ipx routing configured 2204 1241_05_2000_c1 © 2000, Cisco Systems, Inc. 16
  • 9. Agenda • IP, IPX Addressing Concepts • Generic Routing Concepts • Specific Routing Protocols • Static and Defaults Routes 2204 1241_05_2000_c1 © 2000, Cisco Systems, Inc. 17 Convergence • Time required for router to identify and use an alternate path • Dependent on timer values and algorithm • Difficult to predict precisely A,B,C A,B,C B,C D,E,F D,E,F D,E,F 2 4 6 Router’s 5 and 6 C E F B D Have no knowledge of A the new Network A Yet 1 3 A,B,C 5 A,B,C B,C D,E,F D,E,F D,E,F 2204 1241_05_2000_c1 © 2000, Cisco Systems, Inc. 18
  • 10. Load Balancing T1 T1 R2 N1 N2 R1 R4 T1 R3 T1 • Equal cost paths • Rapid failover 2204 1241_05_2000_c1 © 2000, Cisco Systems, Inc. 19 Load Balancing 256K 768K R2 N1 N2 R1 512K R4 R3 T1 • Unequal cost load balancing: Eigrp 2204 1241_05_2000_c1 © 2000, Cisco Systems, Inc. 20
  • 11. Holddown I Will Ignore Routes to X While in Holddown x • Sets minimum convergence time • Prevents forwarding loops 2204 1241_05_2000_c1 © 2000, Cisco Systems, Inc. 21 Forwarding Loop: A Routing Disagreement Packets for Network X • Packets do not get to the destination • Temporary traffic surge until convergence 2204 1241_05_2000_c1 © 2000, Cisco Systems, Inc. 22
  • 12. Split Horizon “ Do not send routing data back in the direction from which it came ” 2204 1241_05_2000_c1 © 2000, Cisco Systems, Inc. 23 Split Horizon Frame Relay Multipoint Network Router 2,3,4 All advertise their Respective Ethernets to Router D, Router D knows all networks PVC 2 A A PVC D 1 3 B B S0 PVC C 4 C 2204 1241_05_2000_c1 © 2000, Cisco Systems, Inc. 24
  • 13. Split Horizon Frame Relay Network Router 1 Advertises network D to routers 2,3,4 2 A PVC PVC D 1 3 B S0 PVC Router 1 4 C Knows all networks but Will only advertise D out of S0 Because it learned A,B,C from S0 2204 1241_05_2000_c1 © 2000, Cisco Systems, Inc. 25 Metrics (Cost) • Numeric value used to choose among paths • RIP/RIPv2 is hop count and ticks (IPX) • OSPF/ISIS is interface cost (bandwidth) • (E)IGRP is compound • BGP can be complicated • Path determination depends on metric 2204 1241_05_2000_c1 © 2000, Cisco Systems, Inc. 26
  • 14. Agenda • IP, IPX Addressing Concepts • Generic Routing Categories • Specific Routing Protocols • Static and Defaults Routes 2204 1241_05_2000_c1 © 2000, Cisco Systems, Inc. 27 Forwarding Table One Forwarding Table per Router One Forwarding Table per Network Protocol Network # Interface Next Hop Metric Age Source 198.113.181.0 Ethernet0 192.150.42.177 [170/304793] 02:03:50 D 198.113.178.0 Ethernet0 192.150.42.177 [110/9936] 02:03:50 O 192.168.96.0 Ethernet0 192.150.42.177 [120/3] 00:00:20 R 192.168.97.0 Ethernet0 C 2204 1241_05_2000_c1 © 2000, Cisco Systems, Inc. 28
  • 15. Building the Forwarding Table • Directly connected Routes that the router is attached to • Static Routes are manually defined • Dynamic Routes protocol are learned from a Protocol 2204 1241_05_2000_c1 © 2000, Cisco Systems, Inc. 29 Routing Protocols I Know About: I Know About: Network A Network X Network B Network Y A Network C Routing Update Network Z X B Y C Exchanges Network Knowledge Z • Routing protocol updates are exchanged by routers to learn about paths to other logical networks • Each routing protocol offers features that can make it desirable as part of an internetwork design 2204 1241_05_2000_c1 © 2000, Cisco Systems, Inc. 30
  • 16. Routing Protocol Goals • Optimal path selection • Easy to configure • Loop-free routing • Adapts to changes easily and quickly • Fast convergence • Does not create a lot • Limited design of traffic administration • Scales to a large size • Minimize update traffic • Compatible with existing • Handle address limitations hosts and routers • Support hierarchical • Supports variable length topology subnet masks and • Incorporate rapid discontiguous subnets convergence • Supports policy routing 2204 1241_05_2000_c1 © 2000, Cisco Systems, Inc. 31 IP RIP • Routing Information • RFC 1058 Protocol • Simple = limited • Widely available • Slow convergence • Hop count metric • No VLSM • Periodic update • No discontiguous • Easy to implement subnets • One of the first • Max 15 Hops available 2204 1241_05_2000_c1 © 2000, Cisco Systems, Inc. 32
  • 17. RIP—Distance Vector Net A Net D R1 R2 R3 Net B Net C E0 S0 S0 S1 S0 E0 Network Interface Network Interface Network Interface A E0 B S0 C S0 B S0 C S1 D E0 C S0 A S0 B S0 D S0 D S1 A S0 Send RIP Routing Table to Neighbors 2204 1241_05_2000_c1 © 2000, Cisco Systems, Inc. 33 Broadcast Routing Updates All Stations Have to Listen to Rip Broadcast’s S 10.1.1.1 D 255.255.255.255 RIP V1 2204 1241_05_2000_c1 © 2000, Cisco Systems, Inc. 34
  • 18. RIP Metric 1 Hop Hops Path A R2 T1 T1 56k R1 R3 Path B 0 Hops 2204 1241_05_2000_c1 © 2000, Cisco Systems, Inc. 35 RIP V2 • RFC 1723 • Cisco IOS® 11.1 support • Advertises masks • Variable length subnet masks • Route summarization • Routing updates use multicast • Authenticated updates using MD5 2204 1241_05_2000_c1 © 2000, Cisco Systems, Inc. 36
  • 19. Multicast Routing Updates RIP V2 2204 1241_05_2000_c1 © 2000, Cisco Systems, Inc. 37 When to Use RIPv2 • Subnet mask support • Reduce broadcast load • Validated updates • Multivendor environment 2204 1241_05_2000_c1 © 2000, Cisco Systems, Inc. 38
  • 20. IPX RIP • Widely available • Tied to SAP protocol • Hop count metric • Simple = limited • Ticks (1/18 sec) • Slow convergence • Periodic update • No default route • Easy to implement • Routing loops • Free on servers • Max 15 hops 2204 1241_05_2000_c1 © 2000, Cisco Systems, Inc. 39 IPX RIP—Ticks • Ticks are used • IPXWAN to determine calculates for server timeout its interfaces • Default for LAN • can be set via interfaces is 1 the ipx delay number interface • Default for WAN sub command interfaces is 4 2204 1241_05_2000_c1 © 2000, Cisco Systems, Inc. 40
  • 21. IGRP • Interior Gateway • Cisco IOS 9.21 Routing Protocol • Periodic update • Cisco developed • No VLSM • Distance vector • Default timers • Compound produce slow metric convergence 2204 1241_05_2000_c1 © 2000, Cisco Systems, Inc. 41 IGRP Compound Metric • Administrative weight T1 R2 • Delay • Bandwidth T1 • Reliability 56k • Load R1 R3 (K2 * BW) K5 = ((K1 * BW + (256-load) + K3* delay)) * (reliability + K )) 4 2204 1241_05_2000_c1 © 2000, Cisco Systems, Inc. 42
  • 22. How the IGRP Metrics Work Delay Metric- D1 D2 D3 Based on D1 + D2 + D3 Bandwidth 1.5 Mbps 64 kbps 1.5 Mbps Metric-Based on 64 kbps • Bandwidth dominates short paths • Delay dominates long paths • Configure bandwidth on all interfaces 2204 1241_05_2000_c1 © 2000, Cisco Systems, Inc. 43 Enhanced IGRP • Extremely fast • Best of DV and LS convergence • Low overhead • VLSM support • Guaranteed • Discontiguous loop-free subnets • Reliable, incremental • Arbitrary route update-based summarization • Multiprotocol: • Supports prefix and IP, IPX®, AppleTalk host routing • Easy to configure 2204 1241_05_2000_c1 © 2000, Cisco Systems, Inc. 44
  • 23. Advanced Distance Vector On Startup Routing Tables Are Exchanged; Routing A 27 Table Built Based on Best B 12 Paths from Topology Table A 1 Z C 35 B 13 C 20 A 27 Z A Q 2 1 Q B Z 13 Q Y 5 X C X 13 B 12 Z .. .. .. Y’s Table A 5 Topology Table B 3 C 3 X • Construct neighbor tables X’s Table • Construct topology tables • Compute routes 2204 1241_05_2000_c1 © 2000, Cisco Systems, Inc. 45 EIGRP Tables • Topology table • Neighbor table • Acted upon by DUAL • Keeps adjacent neighbor’s address • All routes advertised by neighbors • Keeps the hold time • List of neighbors for • Information for each route reliable transport • Routes passive or active 2204 1241_05_2000_c1 © 2000, Cisco Systems, Inc. 46
  • 24. Diffusing Update Algorithm (DUAL) • DUAL is a loop-free routing algorithm that performs a diffused computation of a routing table Uses a new routing algorithm Achieves fast convergence Network changes propagate only to affected nodes (“bounded updates”) • No need for route holddown 2204 1241_05_2000_c1 © 2000, Cisco Systems, Inc. 47 IPX EIGRP • Automatic redistribution of routes into RIP/SAP • Maximum network size is 224 hops vs 15 for RIP • Incremental SAPs sent, reducing bandwidth usage • All other benefits of EIGRP 2204 1241_05_2000_c1 © 2000, Cisco Systems, Inc. 48
  • 25. When to Use EIGRP • Very large, complex networks • VLSM • For fast convergence • Little network design • Multiprotocol support 2204 1241_05_2000_c1 © 2000, Cisco Systems, Inc. 49 Link State Routing Z’s Link State Q’s Link State Topology Information Is Z Kept in a Database Separate from the Forwarding Table A Q 2 B Z 13 Q Y C X 13 • OSPF X X’s Link State • IS-IS • NLSP 2204 1241_05_2000_c1 © 2000, Cisco Systems, Inc. 50
  • 26. Link State Routing • Neighbor discovery • Constructing an LSA (Link State Advertisement) • Distribute LSA • Compute routes using SPF (Shortest Path First) • On network failure New LSAs flooded All routers recompute link state databases 2204 1241_05_2000_c1 © 2000, Cisco Systems, Inc. 51 OSPF • Open Shortest • Fast convergence Path First • Variable-length • Link state or SPF subnet masks technology • Discontiguous • Developed by OSPF subnets working group of • No periodic updates IETF (RFC 1253) • Route authentication • Designed expressly for TCP/IP Internet • Delivered two years environment after IGRP 2204 1241_05_2000_c1 © 2000, Cisco Systems, Inc. 52
  • 27. OSPF Areas and Rules Area • Backbone area (0) Border Router must be present • All other areas Area 2 Area 3 must have Area 0 Internal connection Backbone Router to backbone Router • Backbone must Area 4 be contiguous Area 1 • Do not partition area (0) Autonomous Internet System (AS) Border Router 2204 1241_05_2000_c1 © 2000, Cisco Systems, Inc. 53 When to Use OSPF • Large hierarchical networks • Complex networks, except… Topology restrictive Additional network design • VLSM • Fast convergence • Multivendor 2204 1241_05_2000_c1 © 2000, Cisco Systems, Inc. 54
  • 28. IS-IS • IS = Intermediate • ISO 10589 System • Two types of areas: • Dual IS-IS Level-1 other areas • Integrated IS-IS Level-2 backbone • Metric is 10 bits • Default for wide each level • All interfaces • Much like OSPF default to 10 2204 1241_05_2000_c1 © 2000, Cisco Systems, Inc. 55 NetWare Link Services Protocol • Derived from ISIS • NLSP specs 3 levels of routers • Only two levels are defined • Spec is Novell NLSP version 1.1 http://www.novell.com http://developer.novell.com/research 2204 1241_05_2000_c1 © 2000, Cisco Systems, Inc. 56
  • 29. BGP • RFC 1771 • Many options for policy enforcement • Border Gateway Protocol • Classless Inter Domain Routing • Version 4 is current (CIDR) • Exterior routing • Widely used for protocol (vs. Internet backbone interior) • AS=Autonomous • Uses TCP for systems transport 2204 1241_05_2000_c1 © 2000, Cisco Systems, Inc. 57 BGP Basics Peering A C AS 100 AS 101 B D E • Runs over TCP AS 102 • Path vector protocol • Incremental update 2204 1241_05_2000_c1 © 2000, Cisco Systems, Inc. 58
  • 30. Internal BGP (IBGP) Peering AS 100 D A B E • BGP peer within the same AS • Not required to be directly connected • IBGP neighbors should be fully meshed • Few BGP speakers in corporate network 2204 1241_05_2000_c1 © 2000, Cisco Systems, Inc. 59 External BGP (EBGP) Peering A AS 100 AS 101 C B • Between BGP speakers in different AS • Should be directly connected • Don’t run an IGP between EBGP peers 2204 1241_05_2000_c1 © 2000, Cisco Systems, Inc. 60
  • 31. Policy Drives BGP Requirements AS 200 Static Route BGP AS 100 BGP AS 400 BGP AS 300 • Policy for AS 100: Always use AS 300 path to reach AS 400 2204 1241_05_2000_c1 © 2000, Cisco Systems, Inc. 61 When Not to Use BGP Network Static Number C A ISP Runs BGP B B Advertise Default Network Via IGP Use a Static Route to Provide Connectivity • Avoid BGP configuration by using default networks and static routes Appropriate when the local policy is the same as the ISP policy 2204 1241_05_2000_c1 © 2000, Cisco Systems, Inc. 62
  • 32. Agenda • IP, IPX Addressing Concepts • Generic Routing Categories • Specific Routing Protocols • Static and Defaults Routes 2204 1241_05_2000_c1 © 2000, Cisco Systems, Inc. 63 Static Routes • Routes configured manually • Useful when few or just one route exist • Can be administrative burden • Frequently used for default route 2204 1241_05_2000_c1 © 2000, Cisco Systems, Inc. 64
  • 33. Administrative Distance • The router treats different routing protocols with a different preference Route Source Default Distance Connected Interface 0 Static Route 1 Enhanced IGRP Summary Route 5 External BGP 20 Internal Enhanced IGRP 90 IGRP 100 OSPF 110 IS-IS 115 RIP 120 EGP 140 External Enhanced IGRP 170 Internal BGP 200 Unknown, Discard Route 255 2204 1241_05_2000_c1 © 2000, Cisco Systems, Inc. 65 Floating Static Routes • A static route with a high distance • Can be overridden by dynamic info T1 172.16.3.2 3 172.16.1.0 ISDN C15C0 172.16.3.1 3 ip route 172.16.1.0 255.255.255.0 172.16.3.1 140 ipx route C15C0 3.0000.0c15.3628 floating-static 2204 1241_05_2000_c1 © 2000, Cisco Systems, Inc. 66
  • 34. Default Routes • Route used if no match is found in forwarding table • Can be carried by routing protocols • Two models Special network number: 0.0.0.0 (IP) -2 (IPX) Flagged in routing protocol • Protocols support multiple models 2204 1241_05_2000_c1 © 2000, Cisco Systems, Inc. 67 Creating a Default Route • RIP, RIPv2: network 0.0.0.0 • IGRP, EIGRP: ip default-network • OSPF:ISIS default originate • IPX: ipx route default • default gateway is for “host mode” 2204 1241_05_2000_c1 © 2000, Cisco Systems, Inc. 68
  • 35. Default IP Subnet 172.16.0.0 Internet s0 s1 172.16.1.0 • Two defaults For unknown networks For unknown subnets • Controlled by ip classless 2204 1241_05_2000_c1 © 2000, Cisco Systems, Inc. 69 Comparison of Routing Protocols Link Traditional Advanced Path State Distance Distance Vector Vector Vector Scalability Good Low Excellent Outstanding Bandwidth Low High Low Low Memory High Low Moderate High CPU High Low Low Moderate Convergence Fast Slow Fast Moderate Configuration Moderate Easy Easy Hard 2204 1241_05_2000_c1 © 2000, Cisco Systems, Inc. 70
  • 36. Internet Routing Protocols • IP routing protocols are characterized as Name Type Proprietary Function Updates Metric VLSM Summ RIP DV No Interior 30 Sec Hops No Auto RIPv2 DV No Interior 30 Sec Hops Yes Auto IGRP DV Yes Interior 90 Sec Comp No Auto EIGRP Adv DV Yes Interior Trig Comp Yes Both OSPF LS No Interior Trig Cost Yes Man IS-IS LS No Interior Trig Cost Yes Auto BGP Path Vec No Exterior Incr N/A Yes Auto 2204 1241_05_2000_c1 © 2000, Cisco Systems, Inc. 71 Topology/Technology Considerations • Routing and services overhead is usually not a big deal when you have a lot of bandwidth (i.e. LANs) • Protect WAN bandwidth using update-based protocols—more bandwidth and buffers for application traffic • High densities of sub (interfaces) can cause “hot spots” and router CPU overload • NBMA (Non-Broadcast Multi-Access) technologies always require good design practices 2204 1241_05_2000_c1 © 2000, Cisco Systems, Inc. 72
  • 37. For Further Reference… • EIGRP Network Design Solutions by Ivan Pepelnjak,(ISBN: 1578701651) • Interconnections : Bridges and Routers by Radia Perlman (ISBN: 0-20156-332-0) • Internetworking with TCP / IP, Volume 1: Principles, Protocols, and Architecture by Douglas Comer (ISBN: 0-13216-987-8) • IP Routing Fundamentals by Mark Sportack (ISBN: 1-57870-071-x) • IP Routing Primer by Robert Wright (ISBN: 1-57870-108-2) • OSPF Network Design Solutions by Thomas, Thomas M. (ISBN: 1-57870-046-9) 2204 1241_05_2000_c1 © 2000, Cisco Systems, Inc. 73 For Further Reference… • Routing in the Internet by Christian Huitema (ISBN: 0-13132-192-7) • OSPF Network Design Solutions by Thomas, Thomas M. (ISBN: 1-57870-046-9) • ISP Survival Guide : Strategies for Running a Competitive ISP by Geoff Huston (ISBN:0-47131-499-4) • Internet Routing Architectures by Bassam Halabi (ISBN: 1-56205-652-2) 2204 1241_05_2000_c1 © 2000, Cisco Systems, Inc. 74
  • 38. Thank You! • Related sessions: 2208 Deploying IGRP/EIGRP 2205 Deploying OSPF 2209 Deploying BGP 2200 Advanced IP Routing 2204 1241_05_2000_c1 © 2000, Cisco Systems, Inc. 75 Introduction to Routing Protocols Session 2204 2204 1241_05_2000_c1 © 2000, Cisco Systems, Inc. 76
  • 39. Please Complete Your Evaluation Form Session 2204 2204 1241_05_2000_c1 © 2000, Cisco Systems, Inc. 77 2204 1241_05_2000_c1 © 2000, Cisco Systems, Inc. 78