ACE-BOOKLET-VOL2-Level2-Chanpter5 ( Question #2 Page #52 )

Question

The intermediate router between source and destination do not need the following information in IP header 

a.Protocol

b.Identification number

c.Source IP

d.Version

ans given = ALL FIELDS ARE REQUIRED.

But according to me Identification number is not required at router. because identification number is used for reassembling of packets. and Reassembling is not done at router.

plz clarify.......

Comments

Even i think the same....bcoz reassembly is only done at destination, so router on the way need not have identification no.

Answer 1

Identification no is even required in Routers becase

Routers do Fragmentation of packets in case of MTU size is less than packet size. They will need to include Identification no in Fragments !

Comments

ok got it

Answer 2

Yes, Protocol, Identification number, Source IP and Version, all are required by the intermediate routers.

Identification number is required due to fragmentation done my the intermediate routers. In case of MTU size is less than the size of the packet, so here identification number is required in fragments.

Protocol, Source IP and version are also necessary to process and send the packets correctly.