IPv4 Header Fields (TTL)

Total Len

Fragment ID

Source Address

Destination Address

Header

checksum

Frag Offset

TTL

protocol

TOS

ver

IHL

(options)

32 bits wide

TTL: “time to live”

each router must

decrement by 1

and discard if zero.

Also decremented

if router holds for

longer than 1 sec.

Prevents immortal

datagrams.

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