lec07a - IP datagram format IP protocol version number...

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Network Layer 4-35 IP datagram format ver length 32 bits data (variable length, typically a TCP or UDP segment) 16-bit identifier header checksum time to live 32 bit source IP address IP protocol version number header length (bytes) max number remaining hops (decremented at each router) for fragmentation/ reassembly total datagram length (bytes) upper layer protocol to deliver payload to head. len type of service l type z of data flgs fragment offset upper layer 32 bit destination IP address Options (if any) E.g. timestamp, record route taken, specify list of routers to visit. how much overhead with TCP? ! 20 bytes of TCP ! 20 bytes of IP ! = 40 bytes + app layer overhead
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Network Layer 4-39 IP Addressing: introduction ! IP address: 32-bit identifier for host, router interface ! interface: connection between host/router and physical link " router ` s typically have multiple interfaces " host typically has one interface " IP addresses associated with each interface 223.1.1.1 223.1.1.2 223.1.1.3 223.1.1.4 223.1.2.9 223.1.2.2 223.1.2.1 223.1.3.2 223.1.3.1 223.1.3.27 223.1.1.1 = 11011111 00000001 00000001 00000001 223 1 1 1
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Network Layer 4-40 Subnets ! IP address: " subnet part (high order bits) " host part (low order bits) ! What ` s a subnet ? " device interfaces with same subnet part of IP address " can physically reach each other without intervening router 223.1.1.1 223.1.1.2 223.1.1.3 223.1.1.4 223.1.2.9 223.1.2.2 223.1.2.1 223.1.3.2 223.1.3.1 223.1.3.27 network consisting of 3 subnets subnet
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Network Layer 4-41 Subnets 223.1.1.0/24 223.1.2.0/24 223.1.3.0/24 Recipe ! to determine the subnets, detach each interface from its host or router, creating islands of isolated networks ! each isolated network is called a subnet . Subnet mask: /24
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Network Layer 4-42 Subnets How many? 223.1.1.1 223.1.1.3 223.1.1.4 223.1.2.2 223.1.2.1 223.1.2.6 223.1.3.2 223.1.3.1 223.1.3.27 223.1.1.2 223.1.7.0 223.1.7.1 223.1.8.0 223.1.8.1 223.1.9.1 223.1.9.2
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Network Layer 4-43 IP addressing: CIDR CIDR: C lassless I nter D omain R outing " subnet portion of address of arbitrary length " address format: a.b.c.d/x , where x is # bits in subnet portion of address 11001000 00010111 0001000 0 00000000 subnet part host part 200.23.16.0/23
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Network Layer 4-19 Longest prefix matching Destination Address Range 11001000 00010111 00010*** ********* 11001000 00010111 00011000 ********* 11001000 00010111 00011*** ********* otherwise DA: 11001000 00010111 00011000 10101010 Examples: DA: 11001000 00010111 00010110 10100001 Which interface? Which interface? when looking for forwarding table entry for given destination address, use longest address prefix that matches destination address. Longest prefix matching Link interface 0 1 2 3
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4-68 IPv6 ! Initial motivation: 32-bit address space soon to be completely allocated.
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lec07a - IP datagram format IP protocol version number...

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