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Checksum calculation

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lets say I have client > firewall > server .

firewall is doing nat , my concern is how the checksum at network layer will be calculated . when client will generate a packet and put the checksum info into the header , since the firewall is doing NAT it will change IP header info so when the server receives will it discard the packet because of checksum ??

or is it job of the firewall or any other network device to update the checksum as well if its doing NAT ? if this is the case then in real world scenario , checksum will be calculated and updated ( if required ) at each network device .

asked 14 May '15, 23:57

tech%20round's gravatar image

tech round
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accept rate: 0%


One Answer:

2

or is it job of the firewall or any other network device to update the checksum as well if its doing NAT ?

Yes.

checksum will be calculated and updated ( if required ) at each network device .

every network device that changes parts of the frame, that require recalculation of the checksum, will HAVE TO generate a new checksum, otherwise it will cause massive problems on the network.

Regards
Kurt

answered 15 May '15, 01:20

Kurt%20Knochner's gravatar image

Kurt Knochner ♦
24.8k1039237
accept rate: 15%

edited 15 May '15, 01:20

Thanks Kurt :)

(15 May '15, 07:25) tech round

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(15 May '15, 08:57) grahamb ♦