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Linux Networking Architecture
Hugo
9/11/2014
Outline
• Architecture of Communication System
• Managing Network Packets
• Network Device
• Data-Link Layer
• Network Layer
• Transport Layer
• Sockets in Linux Kernel
• Socket Programming
Outline
• Architecture of Communication System
• Managing Network Packets
• Network Device
• Data-Link Layer
• Network Layer
• Transport Layer
• Sockets in Linux Kernel
• Socket Programming
Linux Kernel Structure
Layer-Based Communication
TCP/IP Reference Model
Vertical & Horizontal Comm.
PDU Protocol Data Unit
PCI Protocol Control Information
SDU Service Data Unit
ICI Interface Control Information
IDU Interface Data Unit
Outline
• Architecture of Communication System
• Managing Network Packets
• Network Device
• Data-Link Layer
• Network Layer
• Transport Layer
• Sockets in Linux Kernel
• Socket Programming
Socket Buffer
• socket buffers are data structures used to represent and manage packets
Layer 4 Layer 3Layer 5-7
Operations on Socket Buffers
• Create, Release, Duplicate Socket Buffers
– alloc_skb(), skb_copy(), skb_copy_expand(),
skb_clone(), kfree_skb(), skb_header_init()
• Manipulate Packet Data Space
– skb_get(), skb_put(), skb_push(),
skb_pull(), skb_tailroom(), skb_headroom(),
skb_realloc_headroom(), skb_reserve(),
skb_trim(), skb_cow()
• Manage Socket Buffer Queues
– skb_cloned(), skb_over_panic(),
skb_under_panic(), skb_head_to_pool(),
skb_head_from_pool()
Socket-Buffer Queue
Operations on Socket-Buffer Queues
• Manage Queue Structures
– skb_queue_head_init(), skb_queue_empty(),
skb_queue_len()
• Manage Socket Buffers in Queues
– skb_queue_head(), skb_queue_tail(),
skb_dequeue(), skb_dequeue_tail(),
skb_queue_purge(), skb_insert(),
skb_append(), skb_unlink(), skb_peek(),
skb_peek_tail()
Outline
• Architecture of Communication System
• Managing Network Packets
• Network Device
• Data-Link Layer
• Network Layer
• Transport Layer
• Sockets in Linux Kernel
• Socket Programming
Network Device Interface
The net_device Structure
• General Fields of a Network Device
– name, next, owner, ifindex, iflink, state, trans_start, last_rx,
priv, qdisc, refcnt, xmit_lock, xmit_lock_owner, queue_lock
• Hardware-Specific Fields
– rmem_end, rmem_start, mem_end, mem_start , base_addr, irq, dma,
if_port
• Data on the Physical Layer
– hard_header_length, mtu, tx_queue_len, type, addr_len, dev_addr,
broadcast, dev_mc_list, mc_count, watchdog_timeo, watchdog_timer
• Data on the Network Layer
– ip_ptr, ip6_ptr, atalk_ptr, dn_ptr, ec_ptr, family, pa_alen,
pa_addr, pa_braddr, pa_mask, pa_dstaddr, flags
• Device-Driver Methods
– init(), uninit(), destructor(), open(), stop(), hard_start_xmit(),
get_stats(), get_wireless_stats(), set_multicast_list(),
watchdog_timeo(), do_ioctl(), set_config(), hard_header(),
rebuild_header(), hard_header_cache(), header_cache_update(),
hard_header_parse(), set_mac_address(), change_mtu()
Managing Network Devices
• Registering and Unregistering Network Devices
– init_netdev(), init_etherdev(), ether_setup(),
register_netdevice(), unregister_netdevice()
• Opening and Closing Network Devices
– dev_open(), dev_close()
• Creating and Finding Network Devices
– dev_alloc_name(), dev_alloc(), dev_get_by_name(),
dev_get_by_index(), dev_load()
• Notification Chains for State Changes
– notifier_call(), notifier_call_chain(),
register_netdevice_notifier(),
unregister_netdevice_notifier()
• Transmitting over Network Devices
– dev_queue_xmit()
Linked List of net_device
Managing Network Drivers
• Initializing Network Adapters
• Opening and Closing a Network Adapter
• Transmitting Data
• Problems In Transmitting Packets
• Runtime Configuration
• Adapter-Specific ioctl() Commands
• Statistical Information About a Network Device
• Multicast Support on Adapter Level
The linux networking architecture
Transmitting Data Packets
static int net_send_packet(struct sk_buff *skb, struct
net_device *dev) {
struct net_local *np = (struct net_local *)dev->priv;
int ioaddr = dev->base_addr;
short length = ETH_ZLEN < skb->len ? skb->len :
ETH_ZLEN;
unsigned char *buf = skb->data;
hardware_send_packet(ioaddr, buf, length);
np->stats.tx_bytes += skb->len;
dev->trans_start = jiffies;
if (inw(ioaddr) == /*RU*/81)
np->stats.tx_aborted_errors++;
dev_kfree_skb (skb);
Interrupts from Network Adapter
Receiving Packets from Adapter
static void net_interrupt(int irq, void *dev_id, struct
pt_regs * regs) {
ioaddr = dev->base_addr;
np = (struct net_local *)dev->priv;
status = inw(ioaddr + 0);
if (status & RX_INTR) {
net_rx(dev);
}
if (status & TX_INTR) {
net_tx(dev);
np->stats.tx_packets++;
netif_wake_queue(dev);
}
Receiving a Data Packet
static void net_rx(struct net_device *dev) {
do {
if (pkt_len == 0)
break;
if (status & 0x40) {
/* There was an error. */
}else{
skb = dev_alloc_skb(pkt_len);
ptr = skb_put(skb,pkt_len);
memcpy(ptr, (void*)dev->rmem_start, pkt_len);
netif_rx(skb);
}
} while (–boguscount);
Acknowledging a Transmission
void net_tx(struct net_device *dev) {
spin_lock(&np->lock);
while (tx_entry_is_sent(np, entry)) {
struct sk_buff *skb = np->skbs[entry];
np->stats.tx_bytes += skb->len;
dev_kfree_skb_irq (skb);
entry = next_tx_entry(np, entry);
}
if (netif_queue_stopped(dev) && ! tx_full(dev))
netif_wake_queue(dev);
spin_unlock(&np->lock);
Outline
• Architecture of Communication System
• Managing Network Packets
• Network Device
• Data-Link Layer
• Network Layer
• Transport Layer
• Sockets in Linux Kernel
• Socket Programming
Media Access & Data-Link Layer
• Data-Link Layer (Ethernet)
• The Serial-Line Internet Protocol (SLIP)
• The Point-to-Point Protocol (PPP)
• PPP over Ethernet
• Asynchronous Transfer Mode—ATM
• Bluetooth in Linux
• Transparent Bridges
Implementation of Data Link Layer
LLC (Logical-Link Control) provide a uniform interface for the upper layer.
MAC (Media-Access Control) handles the media-specific part.
Linux Network Activity
The linux networking architecture
eth_type_trans(skb, dev)
• Recognize the LLC protocol type used and protocol ID of layer-3
• Identify the packet type (unicast, multicast, broadcast)
• Check whether the packet is addressed to the local computer
The linux networking architecture
Internet Protocol Suite
SSH Secure Socket Shell
FTP File Transfer Protocol
DNS Domain Name Service
SMTP Simple Mail Transfer Protocol
TCP Transmission Control Protocol
UDP User Datagram Protocol
IP Internet Protocol
ICMP Internet Control Message Protocol
IGMP Internet Group Management Protocol
ARP Address Resolution Protocol
RARP Reverse Address Resolution Protocol
Outline
• Architecture of Communication System
• Managing Network Packets
• Network Device
• Data-Link Layer
• Network Layer
• Transport Layer
• Sockets in Linux Kernel
• Socket Programming
Network Layer
• IPv4 - Internet Protocol Version 4
• Internet Control Message Protocol (ICMP)
• Address Resolution Protocol (ARP)
• IP Routing
• IP Multicast for Group Communication
• Using Traffic Control to Support Quality of Service (QoS)
• Packet Filters and Firewalls
• Connection Tracking
• Network Address Translation (NAT)
• IPv6 - Internet Protocol Version 6
Internet Protocol
• Provides an unsecured connectionless
datagram service
• Defines IP datagrams as basic units for data
transmission
• Defines the IP addressing scheme
• Routes and forwards IP datagrams across
interconnected networks
• Verifies the lifetime of packets
• Fragments and reassembles packets
• Uses ICMP to output errors
Routing IP Packets between LANs
IP Packet Header
IP Address Classes
The class-A network address 127 represents the loopback network device of a computer.
An IP address with all bits of the computer part set to zero identifies the network itself.
An IP address where the computer part consists of 1-bits defines a broadcast address.
The linux networking architecture
The linux networking architecture
Delivering Packets Locally
• If ip_route_input() is the selected route,
then the packet is addressed to the local
computer. In this case, branching is
to ip_local_deliver() rather than
to ip_forward().
– Reassemble fragmented packets
– ip_local_deliver_finish(): RAW-IP socket or up
to transport layer
Fragmenting an IP Datagram
Each network has a maximum packet size, which is called Maximum
Transfer Unit (MTU). If the MTU of a transmission medium is smaller than
the size of a packet, then the packet has to be split into smaller IP packets.
MTU=1000
MTU=600
The saddr, daddr, id, and protocol elements are keys for the hash
function and the allocation of incoming fragments to their IP datagrams.
Transport-Layer Packets
IP Network Device
IP Options
Class Number Length Name
0 0 - End of Option
0 1 - No Operation
0 2 11 Security
0 3 var Loose Source Routing
0 9 var Strict Source Routing
0 7 var Record Route
0 8 4 Stream ID
2 4 var Internet Timestamp
copy
flag
option
class
option
number
1-bit 2-bit 5-bit
IP Options in the IP layer
Internet Control Message Protocol
• Error-report mechanism for the IP layer.
• The most popular application of ICMP is
error detection or error diagnostics. (ping)
ICMP Packet Header
ICMP Packet Type (RFC 792)
Type Description
Destination Unreachable The destination address cannot be reached.
Time Exceeded A packet was discarded, because its TTL
has expired.
Parameter Problem Unknown or false options.
Source Quench Informs the sender that IP packets were
lost to overload.
Redirect Enables path optimization.
Echo and Echo Reply The data sent to the destination address is
returned in a reply.
Timestamp and Timestamp Reply The timestamp sent to the destination
address is used-to reply with the timestamp
of the destination address.
Information Request und Information Reply Request/reply used to find the network a
computer connects to.
ICMP in the Linux Kernel
• Sending ICMP Packets
– icmp_send()
• Handling Incoming ICMP Packets
– icmp_rcv(), icmp_reply(), icmp_redirect(),
icmp_unreach(), icmp_echo(), icmp_timestamp(),
icmp_addres(), icmp_address_reply()
• ICMP messages generated within the kernel
Address Resolution Protocol
The linux networking architecture
ARP Command
root@tux # arp -a
IP address HW type HW address
129.25.10.97 10Mbit/s Ethernet 49:72:16:08:80:70
129.25.10.72 10Mbit/s Ethernet 49:72:16:08:64:14
129.25.10.81 10Mbit/s Ethernet 49:17:92:96:96:96
The linux networking architecture
The linux networking architecture
Outline
• Architecture of Communication System
• Managing Network Packets
• Network Device
• Data-Link Layer
• Network Layer
• Transport Layer
• Sockets in Linux Kernel
• Socket Programming
Transport Layer
• Transmission Control Protocol (TCP)
• User Datagram Protocol (UDP)
Transmission Control Protocol
• Connection orientation
• Peer-to-peer communication
• Complete reliability
• Full-duplex communication
• Byte-stream interface
• Reliable connection startup
• Graceful connection shutdown
The linux networking architecture
TCP Packet Header
URG points to important data that have to be forwarded immediately.
SYN is used to establish connections. SYN = 1 denotes a connection request.
ACK shows that the ACKNOWLEDGEMENT NUMBER field includes relevant data.
RST can request a connection to be reset. RST = 1 denotes a request to reset a connection.
PSH means that the TCP instance must immediately pass the data received to the higher layers.
FIN means that the connection is to be torn down.
The linux networking architecture
Receiving TCP Segment
The linux networking architecture
The linux networking architecture
The linux networking architecture
Sending TCP Segments
The linux networking architecture
The linux networking architecture
The linux networking architecture
The linux networking architecture
The linux networking architecture
Flow Control
The linux networking architecture
Sliding-Window
Packet Loss & Fast Retransmit
Detecting & Handling Congestions
Congestion Avoidance
User Datagram Protocol
• Same functionality as Internet Protocol (IP)
• Connectionless
• Unreliable service
• Cannot detect and handle lost or duplicate
packets
• Transmitting data easily and quickly
• For audio or video streaming
UDP Packet Format
UDP Header & Payload
Service Interface to App Layer
Outline
• Architecture of Communication System
• Managing Network Packets
• Network Device
• Data-Link Layer
• Network Layer
• Transport Layer
• Sockets in Linux Kernel
• Socket Programming
Socket Support in Linux Kernel
if copy_from_user(a, args, nargs[call]))
return -EFAULT;
a0=a[0];
a1=a[1];
switch(call) {
case SYS_SOCKET:
err = sys_socket(a0,a1,a[2]);
break;
case SYS_BIND:
err = sys_bind(a0, (struct sockaddr *)a1, a[2]);
break;
case SYS_CONNECT:
err = sys_connect (a0, (struct sockaddr *)a1, a[2]);
break;
case SYS_LISTEN:
err = sys_listen (a0,a1);
break;
}
int socket (int family, int type, int protocol)
int bind(int sockfd, struct sockaddr *mAddress, int AddrLength)
int connect(int sockfd, struct sockaddr *ServAddr, int AddrLength)
int listen(int sockfd, int backlog)
sys_socketcall()
BSD Socket
PF_INET Socket
Outline
• Architecture of Communication System
• Managing Network Packets
• Network Device
• Data-Link Layer
• Network Layer
• Transport Layer
• Sockets in Linux Kernel
• Socket Programming
System Calls at Socket Interface
The linux networking architecture
The linux networking architecture
The linux networking architecture
Data Transmission
• Transmitting data
size_t write(sockfd, buffer, length)
int send(sockfd, buffer, length, flags)
int sendto(sockfd, buffer, length, flags, destaddr, addrlen)
• Receiving data
size_t read(sockfd, buffer, length)
int recv(sockfd, buffer, length, flags)
int recvfrom (sockfd, buffer, length, flags, fromaddr,
addrlen)
• Rransmit and receive an array of iovec structures
int readv(int sockfd, const struct iovec *vector, size_t
count)
int writev(int sockfd, const struct iovec *vector, size_t
count)
int sendmsg(int sockfd, const struct msghdr *msg, int flags)
int recvmsg(int sockfd, struct msghdr *msg, int flags)
Q & A
• Architecture of Communication System
• Managing Network Packets
• Network Device
• Data-Link Layer
• Network Layer
• Transport Layer
• Sockets in Linux Kernel
• Socket Programming

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The linux networking architecture

  • 2. Outline • Architecture of Communication System • Managing Network Packets • Network Device • Data-Link Layer • Network Layer • Transport Layer • Sockets in Linux Kernel • Socket Programming
  • 3. Outline • Architecture of Communication System • Managing Network Packets • Network Device • Data-Link Layer • Network Layer • Transport Layer • Sockets in Linux Kernel • Socket Programming
  • 7. Vertical & Horizontal Comm. PDU Protocol Data Unit PCI Protocol Control Information SDU Service Data Unit ICI Interface Control Information IDU Interface Data Unit
  • 8. Outline • Architecture of Communication System • Managing Network Packets • Network Device • Data-Link Layer • Network Layer • Transport Layer • Sockets in Linux Kernel • Socket Programming
  • 9. Socket Buffer • socket buffers are data structures used to represent and manage packets
  • 10. Layer 4 Layer 3Layer 5-7
  • 11. Operations on Socket Buffers • Create, Release, Duplicate Socket Buffers – alloc_skb(), skb_copy(), skb_copy_expand(), skb_clone(), kfree_skb(), skb_header_init() • Manipulate Packet Data Space – skb_get(), skb_put(), skb_push(), skb_pull(), skb_tailroom(), skb_headroom(), skb_realloc_headroom(), skb_reserve(), skb_trim(), skb_cow() • Manage Socket Buffer Queues – skb_cloned(), skb_over_panic(), skb_under_panic(), skb_head_to_pool(), skb_head_from_pool()
  • 13. Operations on Socket-Buffer Queues • Manage Queue Structures – skb_queue_head_init(), skb_queue_empty(), skb_queue_len() • Manage Socket Buffers in Queues – skb_queue_head(), skb_queue_tail(), skb_dequeue(), skb_dequeue_tail(), skb_queue_purge(), skb_insert(), skb_append(), skb_unlink(), skb_peek(), skb_peek_tail()
  • 14. Outline • Architecture of Communication System • Managing Network Packets • Network Device • Data-Link Layer • Network Layer • Transport Layer • Sockets in Linux Kernel • Socket Programming
  • 16. The net_device Structure • General Fields of a Network Device – name, next, owner, ifindex, iflink, state, trans_start, last_rx, priv, qdisc, refcnt, xmit_lock, xmit_lock_owner, queue_lock • Hardware-Specific Fields – rmem_end, rmem_start, mem_end, mem_start , base_addr, irq, dma, if_port • Data on the Physical Layer – hard_header_length, mtu, tx_queue_len, type, addr_len, dev_addr, broadcast, dev_mc_list, mc_count, watchdog_timeo, watchdog_timer • Data on the Network Layer – ip_ptr, ip6_ptr, atalk_ptr, dn_ptr, ec_ptr, family, pa_alen, pa_addr, pa_braddr, pa_mask, pa_dstaddr, flags • Device-Driver Methods – init(), uninit(), destructor(), open(), stop(), hard_start_xmit(), get_stats(), get_wireless_stats(), set_multicast_list(), watchdog_timeo(), do_ioctl(), set_config(), hard_header(), rebuild_header(), hard_header_cache(), header_cache_update(), hard_header_parse(), set_mac_address(), change_mtu()
  • 17. Managing Network Devices • Registering and Unregistering Network Devices – init_netdev(), init_etherdev(), ether_setup(), register_netdevice(), unregister_netdevice() • Opening and Closing Network Devices – dev_open(), dev_close() • Creating and Finding Network Devices – dev_alloc_name(), dev_alloc(), dev_get_by_name(), dev_get_by_index(), dev_load() • Notification Chains for State Changes – notifier_call(), notifier_call_chain(), register_netdevice_notifier(), unregister_netdevice_notifier() • Transmitting over Network Devices – dev_queue_xmit()
  • 18. Linked List of net_device
  • 19. Managing Network Drivers • Initializing Network Adapters • Opening and Closing a Network Adapter • Transmitting Data • Problems In Transmitting Packets • Runtime Configuration • Adapter-Specific ioctl() Commands • Statistical Information About a Network Device • Multicast Support on Adapter Level
  • 21. Transmitting Data Packets static int net_send_packet(struct sk_buff *skb, struct net_device *dev) { struct net_local *np = (struct net_local *)dev->priv; int ioaddr = dev->base_addr; short length = ETH_ZLEN < skb->len ? skb->len : ETH_ZLEN; unsigned char *buf = skb->data; hardware_send_packet(ioaddr, buf, length); np->stats.tx_bytes += skb->len; dev->trans_start = jiffies; if (inw(ioaddr) == /*RU*/81) np->stats.tx_aborted_errors++; dev_kfree_skb (skb);
  • 23. Receiving Packets from Adapter static void net_interrupt(int irq, void *dev_id, struct pt_regs * regs) { ioaddr = dev->base_addr; np = (struct net_local *)dev->priv; status = inw(ioaddr + 0); if (status & RX_INTR) { net_rx(dev); } if (status & TX_INTR) { net_tx(dev); np->stats.tx_packets++; netif_wake_queue(dev); }
  • 24. Receiving a Data Packet static void net_rx(struct net_device *dev) { do { if (pkt_len == 0) break; if (status & 0x40) { /* There was an error. */ }else{ skb = dev_alloc_skb(pkt_len); ptr = skb_put(skb,pkt_len); memcpy(ptr, (void*)dev->rmem_start, pkt_len); netif_rx(skb); } } while (–boguscount);
  • 25. Acknowledging a Transmission void net_tx(struct net_device *dev) { spin_lock(&np->lock); while (tx_entry_is_sent(np, entry)) { struct sk_buff *skb = np->skbs[entry]; np->stats.tx_bytes += skb->len; dev_kfree_skb_irq (skb); entry = next_tx_entry(np, entry); } if (netif_queue_stopped(dev) && ! tx_full(dev)) netif_wake_queue(dev); spin_unlock(&np->lock);
  • 26. Outline • Architecture of Communication System • Managing Network Packets • Network Device • Data-Link Layer • Network Layer • Transport Layer • Sockets in Linux Kernel • Socket Programming
  • 27. Media Access & Data-Link Layer • Data-Link Layer (Ethernet) • The Serial-Line Internet Protocol (SLIP) • The Point-to-Point Protocol (PPP) • PPP over Ethernet • Asynchronous Transfer Mode—ATM • Bluetooth in Linux • Transparent Bridges
  • 28. Implementation of Data Link Layer LLC (Logical-Link Control) provide a uniform interface for the upper layer. MAC (Media-Access Control) handles the media-specific part.
  • 31. eth_type_trans(skb, dev) • Recognize the LLC protocol type used and protocol ID of layer-3 • Identify the packet type (unicast, multicast, broadcast) • Check whether the packet is addressed to the local computer
  • 33. Internet Protocol Suite SSH Secure Socket Shell FTP File Transfer Protocol DNS Domain Name Service SMTP Simple Mail Transfer Protocol TCP Transmission Control Protocol UDP User Datagram Protocol IP Internet Protocol ICMP Internet Control Message Protocol IGMP Internet Group Management Protocol ARP Address Resolution Protocol RARP Reverse Address Resolution Protocol
  • 34. Outline • Architecture of Communication System • Managing Network Packets • Network Device • Data-Link Layer • Network Layer • Transport Layer • Sockets in Linux Kernel • Socket Programming
  • 35. Network Layer • IPv4 - Internet Protocol Version 4 • Internet Control Message Protocol (ICMP) • Address Resolution Protocol (ARP) • IP Routing • IP Multicast for Group Communication • Using Traffic Control to Support Quality of Service (QoS) • Packet Filters and Firewalls • Connection Tracking • Network Address Translation (NAT) • IPv6 - Internet Protocol Version 6
  • 36. Internet Protocol • Provides an unsecured connectionless datagram service • Defines IP datagrams as basic units for data transmission • Defines the IP addressing scheme • Routes and forwards IP datagrams across interconnected networks • Verifies the lifetime of packets • Fragments and reassembles packets • Uses ICMP to output errors
  • 37. Routing IP Packets between LANs
  • 39. IP Address Classes The class-A network address 127 represents the loopback network device of a computer. An IP address with all bits of the computer part set to zero identifies the network itself. An IP address where the computer part consists of 1-bits defines a broadcast address.
  • 42. Delivering Packets Locally • If ip_route_input() is the selected route, then the packet is addressed to the local computer. In this case, branching is to ip_local_deliver() rather than to ip_forward(). – Reassemble fragmented packets – ip_local_deliver_finish(): RAW-IP socket or up to transport layer
  • 43. Fragmenting an IP Datagram Each network has a maximum packet size, which is called Maximum Transfer Unit (MTU). If the MTU of a transmission medium is smaller than the size of a packet, then the packet has to be split into smaller IP packets. MTU=1000 MTU=600
  • 44. The saddr, daddr, id, and protocol elements are keys for the hash function and the allocation of incoming fragments to their IP datagrams.
  • 47. IP Options Class Number Length Name 0 0 - End of Option 0 1 - No Operation 0 2 11 Security 0 3 var Loose Source Routing 0 9 var Strict Source Routing 0 7 var Record Route 0 8 4 Stream ID 2 4 var Internet Timestamp copy flag option class option number 1-bit 2-bit 5-bit
  • 48. IP Options in the IP layer
  • 49. Internet Control Message Protocol • Error-report mechanism for the IP layer. • The most popular application of ICMP is error detection or error diagnostics. (ping)
  • 51. ICMP Packet Type (RFC 792) Type Description Destination Unreachable The destination address cannot be reached. Time Exceeded A packet was discarded, because its TTL has expired. Parameter Problem Unknown or false options. Source Quench Informs the sender that IP packets were lost to overload. Redirect Enables path optimization. Echo and Echo Reply The data sent to the destination address is returned in a reply. Timestamp and Timestamp Reply The timestamp sent to the destination address is used-to reply with the timestamp of the destination address. Information Request und Information Reply Request/reply used to find the network a computer connects to.
  • 52. ICMP in the Linux Kernel • Sending ICMP Packets – icmp_send() • Handling Incoming ICMP Packets – icmp_rcv(), icmp_reply(), icmp_redirect(), icmp_unreach(), icmp_echo(), icmp_timestamp(), icmp_addres(), icmp_address_reply() • ICMP messages generated within the kernel
  • 55. ARP Command root@tux # arp -a IP address HW type HW address 129.25.10.97 10Mbit/s Ethernet 49:72:16:08:80:70 129.25.10.72 10Mbit/s Ethernet 49:72:16:08:64:14 129.25.10.81 10Mbit/s Ethernet 49:17:92:96:96:96
  • 58. Outline • Architecture of Communication System • Managing Network Packets • Network Device • Data-Link Layer • Network Layer • Transport Layer • Sockets in Linux Kernel • Socket Programming
  • 59. Transport Layer • Transmission Control Protocol (TCP) • User Datagram Protocol (UDP)
  • 60. Transmission Control Protocol • Connection orientation • Peer-to-peer communication • Complete reliability • Full-duplex communication • Byte-stream interface • Reliable connection startup • Graceful connection shutdown
  • 62. TCP Packet Header URG points to important data that have to be forwarded immediately. SYN is used to establish connections. SYN = 1 denotes a connection request. ACK shows that the ACKNOWLEDGEMENT NUMBER field includes relevant data. RST can request a connection to be reset. RST = 1 denotes a request to reset a connection. PSH means that the TCP instance must immediately pass the data received to the higher layers. FIN means that the connection is to be torn down.
  • 77. Packet Loss & Fast Retransmit
  • 78. Detecting & Handling Congestions
  • 80. User Datagram Protocol • Same functionality as Internet Protocol (IP) • Connectionless • Unreliable service • Cannot detect and handle lost or duplicate packets • Transmitting data easily and quickly • For audio or video streaming
  • 82. UDP Header & Payload
  • 83. Service Interface to App Layer
  • 84. Outline • Architecture of Communication System • Managing Network Packets • Network Device • Data-Link Layer • Network Layer • Transport Layer • Sockets in Linux Kernel • Socket Programming
  • 85. Socket Support in Linux Kernel
  • 86. if copy_from_user(a, args, nargs[call])) return -EFAULT; a0=a[0]; a1=a[1]; switch(call) { case SYS_SOCKET: err = sys_socket(a0,a1,a[2]); break; case SYS_BIND: err = sys_bind(a0, (struct sockaddr *)a1, a[2]); break; case SYS_CONNECT: err = sys_connect (a0, (struct sockaddr *)a1, a[2]); break; case SYS_LISTEN: err = sys_listen (a0,a1); break; } int socket (int family, int type, int protocol) int bind(int sockfd, struct sockaddr *mAddress, int AddrLength) int connect(int sockfd, struct sockaddr *ServAddr, int AddrLength) int listen(int sockfd, int backlog) sys_socketcall()
  • 89. Outline • Architecture of Communication System • Managing Network Packets • Network Device • Data-Link Layer • Network Layer • Transport Layer • Sockets in Linux Kernel • Socket Programming
  • 90. System Calls at Socket Interface
  • 94. Data Transmission • Transmitting data size_t write(sockfd, buffer, length) int send(sockfd, buffer, length, flags) int sendto(sockfd, buffer, length, flags, destaddr, addrlen) • Receiving data size_t read(sockfd, buffer, length) int recv(sockfd, buffer, length, flags) int recvfrom (sockfd, buffer, length, flags, fromaddr, addrlen) • Rransmit and receive an array of iovec structures int readv(int sockfd, const struct iovec *vector, size_t count) int writev(int sockfd, const struct iovec *vector, size_t count) int sendmsg(int sockfd, const struct msghdr *msg, int flags) int recvmsg(int sockfd, struct msghdr *msg, int flags)
  • 95. Q & A • Architecture of Communication System • Managing Network Packets • Network Device • Data-Link Layer • Network Layer • Transport Layer • Sockets in Linux Kernel • Socket Programming