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Ch 21. Other IP-related Protocols

Ch 21. Other IP-related Protocols. 21.1 Address Mapping. IP packets use logical address , and need to be encapsulated in a frame at data link layer, which requires physical address Address Resolution Protocol (ARP) ARP request – broadcast ARP reply – unicast

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Ch 21. Other IP-related Protocols

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  1. Ch 21. Other IP-related Protocols

  2. 21.1 Address Mapping • IP packets use logical address, and need to be encapsulated in a frame at data link layer, which requires physical address • Address Resolution Protocol (ARP) • ARP request – broadcast • ARP reply – unicast • Information is cached at the sender

  3. ARP Packet Format Length of the physical address Length of the logical address

  4. Example • The sender A and the receiver B are hosts (local network). IP is mapped to a physical address. • The sender A is a host and the receiver B is a router. (packet is sent to another network) • The sender A and receiver B are routers (sent to another network). • The sender A is a router and the receiver B is a host.

  5. Proxy ARP • When a local network consists of multiple subnetworks

  6. Other Address Mapping • Reverse Address Resolution Protocol (RARP) • Find a logical address corresponding to a physical address • Bootstrap Protocol (BOOTP) • Application level protocol to provide mapping from physical address to logical address • Set source IP address to all 0’s, and set destination IP address to all 1’s • Dynamic Host Configuration Protocol (DHCP) • Provides static and dynamic address allocation that can be manual or automatic • A host may move from one network to another • DHCP provides temporary IP addresses

  7. 21.2 ICMP • IP provides unreliable and connectionless datagram delivery. It lacks of error control and assistance mechanisms. • What happens if • a router must discard a datagram because it cannot fined a router; • or time to live field has a zero value • The final destination host must discard all fragments of a datagram because it is not received all fragments, with a predetermined time limit. • Internet Control Message Protocol • Error-reporting (about a router or a host) or query message

  8. Error Reporting • Encapsulation of error reporting message • Copy (IP headers + 8 bytes data) of the received pkt

  9. Query Message • Encapsulation of query message

  10. ICMP Application • “ping” • To find if a host is alive • ICMP echo-request and echo-reply message

  11. ICMP Application • “traceroute” (in Unix; “tracert” in Windows) • To find the route of a packet • ICMP time-exceeded message Nowadays, many hosts and routers do not respond (or a gateway blocks the packets) due to security reason

  12. 21.3 IGMP • Multicasting: one-to-many communication • Internet Group Management Protocol (IGMP) • One of protocols necessary for multicasting • Manage group membership • Operations • Join a group • Leave a group • Monitor membership – Server periodically sends a query to ensure membership. Hosts use a delayed response to reduce traffic

  13. Encapsulation • Encapsulation into IP datagram and frame • IP packet with an ICMP message has a value of “1” in its TTL field  IGMP works locally • IP destinationaddress

  14. Encapsulation at data link layer • Multicast support (most LANs) – map multicast IP address to physical address (many-to-one) • No multicast support (most WANs) – use tunneling • Application “netstat”

  15. Homework • Exercise • 17 • 19 • 22 • 23 • 25

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