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Internetworking

Internetworking. Network 4. (point-to-point). R1. R2. A Simple Internetwork. Network 1 (Ethernet). Hn = Host. Rn = Router. H7. R3. H8. H1. H2. H3. (router=gateway). Network 2 (Ethernet). H4. Network 3 (Token Ring). H5. H6. Protocol Layers. IP Service Model.

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Internetworking

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  1. Internetworking

  2. Network 4 (point-to-point) R1 R2 A Simple Internetwork Network 1 (Ethernet) Hn = Host Rn = Router H7 R3 H8 H1 H2 H3 (router=gateway) Network 2 (Ethernet) H4 Network 3 (Token Ring) H5 H6

  3. Protocol Layers

  4. IP Service Model • Packet Delivery Model • Best Effort • Global Addressing Scheme • IP Addresses

  5. Packet Delivery Model • Connectionless (datagram-based) • Best-effort delivery (unreliable service) • packets are lost • packets are delivered out of order • duplicate copies of a packet are delivered • packets can be delayed for a long time

  6. Why is the Internet so slow? MAE-East, MAE-West, PacBell NAP

  7. 20+ Network Access Points Internap is Dr. Ekstrom’s company

  8. Trunks • Most Trunks are SONET rings • Sprint, AT&T, UUNET (MCI) all have their own rings • They run data and voice on SONET

  9. NSFNET

  10. A Partial Internet Trunk MapShowing ISP Access Lines

  11. US Main Internet connections

  12. Visual Traceroute

  13. Datagram format • Version (4): currently 4 • Hlen (4): number of 32-bit words in header • TOS (8): type of service (not widely used QoS) • Length (16): number of bytes in this datagram • Ident (16): different for each datagram • Flags/Offset (16): used by fragmentation • TTL (8): number of hops this datagram has traveled • Protocol (8): demux key (TCP=6, UDP=17) • Checksum (16): of the header only • DestAddr & SrcAddr (32)

  14. Fragmentation and Reassembly • Each network has some MTU • Strategy • fragment when necessary (MTU < Datagram) • try to avoid fragmentation at source host • refragmentation is possible • fragments are self-contained datagrams • use CS-PDU (not cells) for ATM • delay reassembly until destination host • do not recover from lost fragments • Fragment on 8 byte boundaries • Drop the last 3 bits of the offset field

  15. Example

  16. What about Encryption? • Total security requires • Contents of datagram cannot be read (data) • Destination and source cannot be determined • Every Router must have encryption key if packets are going to be fragmented • Some protocols require not fragmentation for security reasons.

  17. What about Filtering Firewalls • Half of login name can be in each fragment • Half of URL can be in each packet • Must reassemble in firewall if filtering is to be performed.

  18. Global Addresses • Properties • globally unique • hierarchical: network + host • Format • Dot notation • 10.3.2.4 • 128.96.33.81 • 192.12.69.77 7 24 0 network host Class A 14 16 1 0 network host Class B 21 8 1 1 0 network host Class C

  19. Datagram Forwarding • Strategy • every datagram contains destination's address • if directly connected to destination network, then forward to host • if not directly connected to destination network, then forward to some router • forwarding table maps network number into next hop • each host has a default router • each router maintains a forwarding table

  20. Forwarding Table • Network Number • Network Mask • Interface • Default Route

  21. My machine C:\>netstat -r Network destination Netmask Gateway Interface Metric 0.0.0.0 0.0.0.0 128.187.172.1 128.187.172.116 1 127.0.0.0 255.0.0.0 127.0.0.1 127.0.0.1 1 128.187.172.0 255.255.255.0 128.187.172.116 128.187.172.116 1 128.187.172.116 255.255.255.255 127.0.0.1 127.0.0.1 1 128.187.255.255 255.255.255.255 128.187.172.116 128.187.172.116 1 255.255.255.255 255.255.255.255 128.187.172.116 128.187.172.116 1 Default Gateway: 128.187.172.1

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