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Understanding IP Routing, ICMP, and IGMP: Key Concepts of Internet Protocols

This lecture, presented by Dr. Li-Chuan Chen, focuses on the critical aspects of IP routing and related protocols, including Internet Control Message Protocol (ICMP) and Internet Group Management Protocol (IGMP). We explore how packets are routed through networks, differentiating between direct and indirect delivery methods. The lecture highlights routing table management, various routing strategies like host-specific, network-specific, and next-hop routing, and the critical role of protocols in error reporting and network diagnostics. Gain insights into efficient routing and methods for handling incoming datagrams in a network environment.

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Understanding IP Routing, ICMP, and IGMP: Key Concepts of Internet Protocols

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  1. TCOM 509 – Internet Protocols (TCP/IP)Lecture 05_aInternet Protocol: Routing IP Datagrams, ICMP, IGMP Instructor: Dr. Li-Chuan ChenDate: 09/29/2003

  2. Routing In An Internet • IP Routing: determine best route to forward packets from source to destination through the networks. • Direct Delivery: deliver a packet from source to destination within the same physical network without using routers. • Indirect Delivery: deliver a packet from source to destination from source to destination through various networks using routers.

  3. IP Routing • Internet (IP) routing table • stores information about possible destinations and how to reach them • Routing Methods – Table-Driven • Host-specific • Network-specific • Next-Hop • Default Routes

  4. Host-Specific Routing • Routing table contains all destination IP address • Pros • More control over network use • Access control for security • Debugging network connections or routing tables • Cons • routing tables becomes too big for Internet • routing inefficient

  5. Network-Specific Routing • Routing table contains only network portion of IP address • Pros • routing tables small • routing efficient • Cons • All traffic must take the same path for the same destination network • Only the final router can determine if the host is up or down • Path A  B may be different from B  A

  6. Next-Hop Routing • Using a routing table to store a next hop for each destination. • Routing table contains (N,R), where • N is the destination IP address • R is the next router IP address (next hop) • Pros • Routing table is small • Efficient

  7. Example Routing Table for R2 Network 4 40.0.0.0 20.0.0.5 30.0.0.6 40.0.0.7 Network 3 30.0.0.0 Network 1 10.0.0.0 Network 2 20.0.0.0 R3 R1 R2 30.0.0.7 10.0.0.5 20.0.0.6

  8. Default Routes • If no routes available in the routing table, then send packet to a default router. • Useful when only one router connect to the rest of internet. Pros • Routing is simple (either local network or use a default for all other destination).

  9. Routing Algorithm Extract destination IP address, D, and compute the network prefix, N • If N matches direct network connectionThen resolving D to a MAC address, encapsulating the datagram, and send it • Else if host-specific route found Then send the datagram • Else if entry exists for network N, send it • Else if entry exists for default route, send it • Else routing error

  10. Routing With IP Address • IP routing does not change the original datagram except • Time to live • Checksum • Where does it store the next hop address? • IP pass the info to the network interface software (nis) • nis binds the next hop address to a physical address • Why not store the physical address instead? • Easy to understand, test, modify, and debug routing problems • Hide details of underlying networks

  11. Handling Incoming Datagrams Host • nis delivers packet to IP module • If destination IP address matchesThen pass it to the higher-level protocolElse discard the packet

  12. Handling Incoming Datagrams Router • Unlike hosts, routers forward the packet if not reach the final destination • If not match any of the local host addresses • Decrement time to live • if the count is 0, discard the packet • Else compute a new checksum and route the packet

  13. Handling Incoming Datagrams Why can’t a host forward a datagram? • Network problems may not surfaced • Waste host resource (CPU time) • Unnecessary network traffic • Error reports won’t be sending back to the original source

  14. Internetworking Protocols

  15. Internet Control Message Protocol (ICMP) used by hosts, routers, gateways to communication network-level information error reporting unreachable host, network, port, protocol Errors are reporting back to the sender diagnostic: echo request/reply (used by ping) network-layer “above” IP: ICMP msgs encapsulated in IP datagrams ICMP message:type, code, ICMP checksum, plus first 8 bytes of IP datagram causing error, ICMP

  16. ICMP Header ICMP Data Datagram Header Datagram Data Frame Header Frame Data ICMP Message Encapsulation 8-byte Variable-size Protocol Field in IP datagram = 1 for ICMP

  17. Error-Reporting Destination unreachable (Type 3) Source quench (Type 4) Time exceeded (Type 11) Parameter Problem (Type 12) Redirection (Type 5) Query Echo request or reply (Type 8 or 0) Timestamp request or reply (Type 13 or 14) Address mask request or reply (Type 17 or 18) Router advertisement or solicitation (Type 9 or 10) ICMP Message Types

  18. ICMP Messages TypeCodedescription 0 0 echo reply (ping) – host or router 3 0 dest. network unreachable - router 3 1 dest host unreachable - router 3 2 dest protocol unreachable (tcp, udp, ospf) - host 3 3 dest port unreachable - host 3 6 dest network unknown - router 3 7 dest host unknown - router 4 0 source quench (congestion control) - host or router 5 0-3 Redirect (change a route) - router 8 0 echo request (ping) – host or router 9 0 router advertisement - router 10 0 router solicitation - host 11 0 TTL expired - router11 1 Fragment reassembly expired - host 12 0 bad IP header – host or route 13 0 Timestamp-request (round-trip time) – host or router 14 0 Timestamp-respond (round-trip time) – host or router

  19. No ICMP error messages will be generated for the following rules: IP carrying ICMP message Fragment datagram that is not the first fragment Datagram contains multicast address Datagram contains 127.0.0.0 or 0.0.0.0 ICMP

  20. Multicast: act of sending datagram to multiple receivers with single “transmit” operation Question: how to achieve multicast Multicast via unicast • source sends N unicast datagrams, one addressed to each of N receivers routers forward unicast datagrams multicast receiver (red) not a multicast receiver (grey) Multicast: one sender to many receivers

  21. Multicast: act of sending datagram to multiple receivers with single “transmit” operation analogy: one teacher to many students Question: how to achieve multicast Multicast: one sender to many receivers Network multicast • Router actively participate in multicast, making copies of packets as needed and forwarding towards multicast receivers Multicast routers (red) duplicate and forward multicast datagrams

  22. Multicast: act of sending datagram to multiple receivers with single “transmit” operation analogy: one teacher to many students Question: how to achieve multicast Multicast: one sender to many receivers Application-layer multicast • end systems involved in multicast copy and forward unicast datagrams among themselves

  23. Internet Multicast Service Model 128.59.16.12 multicast group concept: use of indirection • hosts addresses IP datagram to multicast group • routers forward multicast datagrams to hosts that have “joined” that multicast group 128.119.40.186 multicast group 226.17.30.197 128.34.108.63 128.34.108.60

  24. Multicast groups • class D Internet addresses reserved for multicast: • host group semantics: • anyone can “join” (receive) multicast group • anyone can send to multicast group • no network-layer identification to hosts of members • needed: infrastructure to deliver mcast-addressed datagrams to all hosts that have joined that multicast group

  25. IGMP IGMP wide-area multicast routing IGMP Joining a mcast group: two-step process • local: host informs local mcast router of desire to join group: IGMP (Internet Group Management Protocol) • wide area: local router interacts with other routers to receive mcast datagram flow • many protocols (e.g., DVMRP, MOSPF, PIM) • DVMRP: Distance Vector Multicast Routing Protocol • MOSPF: Multicast OSPF • PIM: Protocol Independent Multicast

  26. IGMP: Internet Group Management Protocol • A protocol that manages group membership. • IGMP Message Types • Query (Type 0x11) • General: sent every 125 sec with group address 0.0.0.0 • Special: specific group address • Membership Report (Type 0x16) • Leave Report (Type 0x17) • For each group, only one router handles multicast packets for that group. • Query router • Query messages may crate a lot of responses. To avoid unnecessary traffic, designate one router as the query router for each network. Other routers receives responses and update their lists.

  27. report query IGMP: Internet Group Management Protocol • host: sends IGMP membership report when application joins mcast group • Membership report is sent twice, one after antoher. • router:sends IGMP query at regular intervals • host belonging to a mcast group must reply to query

  28. IGMP version 1 router: Host Membership Query msg broadcaston LAN to all hosts host: Host Membership Report msg to indicate group membership randomized delay before responding implicit leave via no reply to Query RFC 1112 IGMP v2: group-specific Query Leave Group msg last host replying to Query can send explicit Leave Group msg router performs group-specific query to see if any hosts left in group RFC 2236 IGMP v3:under development as Internet draft IGMP

  29. IGMP Header IGMP Group Address Datagram Header Datagram Data Frame Header Frame Data IGMP Message Encapsulation 4-byte 4-byte • IP datagram field: • IP Destination Address - • Query: 224.0.0.1 All host and routers • Leave: 224.0.0.2 All routers • Membership: The multicast group address • IP datagram field: • Protocol Field = 2 for IGMP • TTL = 1, only valid within the LAN

  30. Most WANs do not support physical multicast addressing. Solution: usetunneling Multicast packet is encapsulated in a unicast packet and sent through the network IGMP Header IGMP Group Address Datagram Header Multicast DatagramData Header IP Unicast Data Multicats Tunneling 4-byte 4-byte

  31. Read Chapter 8: all sections Chapter 9: 9.1 – 9.13 Chapter 17: 17.1 – 17.16 Assignments

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