Lecture 9: Internetworking - University of California, San Diego

Lecture 9: Internetworking

CSE 123: Computer Networks Alex C. Snoeren

Lecture 9 Overview

? IP Fragmentation ? ICMP, the other network-layer protocol ? IP Addresses

? Class-based addressing

CSE 123 ? Lecture 9: Internetworking

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IP Philosophy

! Impose few demands on network

u Make few assumptions about what network can do u No QoS, no reliability, no ordering, no large packets u No persistent state about communications; no connections

! Manage heterogeneity at hosts (not in network)

u Adapt to underlying network heterogeneity u Re-order packets, detect errors, retransmit lost messages... u Persistent network state only kept in hosts (fate-sharing)

! Service model: best effort, a.k.a. send and pray

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IP Packet Header

0

15 16

ver HL TOS

length

identification

RMD

E F F offset

S

TTL

protocol header checksum

source address

31

20 bytes

destination address

options (if any)

data (if any)

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Version field

! Which version of IP is this?

u Plan for change u Very important!

What versions of IP are in use today?

A. IPv4 B. IPv6 C. Both v4 and v6 D. More than two

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