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Internet Protocol

Internet Protocol. Connectionless Network Layers. Destination, source, hop count Maybe other stuff fragmentation options (e.g., source routing) error reports special service requests (priority, custom routes) congestion indication Real diff: size of addresses. IPv4 Packet Header.

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Internet Protocol

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  1. Internet Protocol

  2. Connectionless Network Layers • Destination, source, hop count • Maybe other stuff • fragmentation • options (e.g., source routing) • error reports • special service requests (priority, custom routes) • congestion indication • Real diff: size of addresses

  3. IPv4 Packet Header Version (4 b) hdr lnth (4 b) TOS 1 2 total length pkt id 2 df mf (3 b) offset offset (cont’d) 1 1 TTL (time to live) Don’t Fragment More Fragments protocol hdr checksum 2 source 4 TCP, UDP destination 4 Variable (<40B) options padding variable

  4. Collection of Subnetworks The Internet is an interconnected collection of many networks.

  5. IP Addresses • IP addresses are given to • Computers • Router interfaces • Each address comprises network address and host address • Mask comprises ones in the positions of a network address and zeros in the positions of a host address. It is “anded” with the packet IP destination address, and routed based on the network address.

  6. Classful IP Addresses IP address formats. Class A: 126 networks with 16 million users Class B: 16384 networks with 64K users Class C: 2 million networks with 256(-2) users

  7. Network address Network 0 0 … 0 0 Special IP Addresses

  8. Subnets A campus network consisting of LANs for various departments. Switch, repeater

  9. Subnets • A part of the host address is used as the subnet address • Each router interface is given an IP address and a mask that corresponds to the subnet address. • Packets are routed based on subnet addresses. • The number of addresses in the router memory is significantly decreased. Routing decision simplified.

  10. Subnets A class B network subnetted into 64 subnets with 1022 hosts. Example starts at 243.15.24.1/22 to 243.15.27.254/22

  11. CIDR – Classless Inter Domain Routing • Subnets can be arbitrary sizes, masks arbitrary lengths. • Packets of one subnet are most often routed toward different subnet. • Routers match the IP destination address with subnet addresses. Packet is routed toward the subnet whose address is the longest prefix of the IP destination address, and which is stored in the observed router.

  12. CIDR 5-59 194.24.0.0/20 ISP Provider

  13. ARP– The Address Resolution Protocol • User knows only IP address of the destination (which is learnt from a DNS server), but it needs the destination MAC address. • It broadcasts ARP request with the destination IP address, and the destination responds with its address. • Alternatively if the destination is not on the same LAN, router sends ARP response (proxy ARP) with its MAC address, or user knows from the IP address that its destination is not on LAN, it sends a frame to the router MAC address.

  14. ARP– The Address Resolution Protocol Three interconnected /24 networks: two Ethernets and an FDDI ring.

  15. User Learns its Own Address • User should learn its own IP address. • RARP (Reverse ARP): user broadcasts request for the IP address providing its MAC address. • BOOTP: user sends the request for its IP address to the designated router, which forwards the request to the network. Administrator has to assign IP for each MAC address manually.

  16. DHCP- Dynamic Host Configuration Protocol • User broadcasts request for IP address. • DHCP relay agent learns about the request, and sends it to the remote DHCP server which leases to the user first available address.

  17. DHCP- Dynamic Host Configuration Protocol Operation of DHCP.

  18. IPv6 vers TOS flow label (20 bits) (4 bits) (8 bits) payload length (2 B) Next (1 B) Hops (1 B) Source (128 bits) Destination (128 bits) hop by hop hdr, or dest info, or authentication hdr, or fragmentation hdr ...

  19. cost 2 j m cost 3 I am “4” cost 7 cost 2 k n Distance Vector Routing • Rtr knows • own ID • how many cables hanging off box • cost, for each cable, of getting to nbr

  20. Distance Vector (DV) Routing • Initialize distances to all rtrs in the network to be 0, except to its nbrs. • Rtr learns from nbrs their distances to all nodes in the network, calculate own distances, and forward the distance vector to nbrs. This repeats until the distance vector converges. • Rtr updates the distance vector whenever it receives different distance vector from some nbr, or whenever some link breaks. • Distance vector is either sent periodically or when the network configuration changes.

  21. Example of DV Routing cost 2 j m cost 3 I am “4” cost 7 cost 2 k n distance vector rcv’d from cable j cost 3 12 3 15 3 12 5 3 18 0 7 15 distance vector rcv’d from cable k cost 2 5 8 3 2 10 7 4 20 5 0 15 distance vector rcv’d from cable m cost 2 0 5 3 2 19 9 5 22 2 4 7 distance vector rcv’d from cable n cost 7 6 2 0 7 8 5 8 12 11 3 2 your own calculated distance vector 2 6 5 0 12 8 6 19 3 ? ? your own calculated forwarding table m j m 0 k j k/j n j ? ?

  22. Link State Routing • Construct Link State Packet (LSP) • who you are • list of (nbr, cost) pairs • Broadcast LSPs to all rtrs • Store latest LSP from each rtr received from nbrs • Compute Routes • Forward LSPs from each nbr to other nbrs

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