u Counted in 32 bit words u Variable length Options u Engineering consequences

U counted in 32 bit words u variable length options u

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u Counted in 32-bit words u Variable length » Options u Engineering consequences of variable length… Most IP packet headers are 20 bytes long 8 CSE 123 – Lecture 9: Internetworking What is the content of the HL field for most IP packets? A. 20 B. 5 C. Something else
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Type - of - Service How should this packet be treated? u Care/don’t care for delay, throughput, reliability, cost u How to interpret, how to apply on underlying net? u Largely unused until 2000 (hijacked for new purposes, ECN & Diffserv) 9 CSE 123 – Lecture 9: Internetworking
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TTL (Time - to - Live) How many more routers can this packet pass through? u Designed to limit packet from looping forever Each router decrements TTL field If TTL is 0 then router discards packet 10 CSE 123 – Lecture 9: Internetworking
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Protocol Which transport protocol is the data using? u i.e. how should a host interpret the data TCP = 6 UDP = 17 11 CSE 123 – Lecture 9: Internetworking
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IP Checksum Header contains simple checksum u Validates content of header only Recalculated at each hop u Routers need to update TTL u Hence straightforward to modify Ensures correct destination receives packet 12 CSE 123 – Lecture 9: Internetworking
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Length How long is whole packet in bytes?
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  • Fall '08
  • Varghese,G

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