NAT two hops after

Answered Question
Jul 25th, 2007

hello ppl

there is a sw3550 hosting a lan 10.1.1.0 which is connected with another sw3550 miles away with FO which is hosting a lan 10.2.2.0 which is connected with a router into a fasthernet interface...

Also there is routing on both 3550 enabled and all three devices are in a row.

That fast ethernet interface from the router has already a NAT for the 10.2.2.0 lan but i want to add the first lan too 10.1.1.0 .

Because those lans connected in a row is there any conflict when the get nated at the same nat inside interace...

Its not so clear to me if the packets comes from the 10.1.1.0 looks like the generated from the second lan or they recognized as ip source 10.2.2.0 .


thanks a lot

Correct Answer by Jon Marshall about 9 years 7 months ago

Hi


Can you explain what you mean by first network passes through second.


Where are the routed interfaces for the


10.1.1.0/24 network

10.2.2.0/24 network


IP packets always keep the same source IP unless your are natting but natting does not encapsulate the packet.


If you are tunneling you would be using encapsulation but it doesn't sound from your description as though that is what you are doing.


Jon

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Jon Marshall Wed, 07/25/2007 - 10:53

Hi


If i understand correctly you just want to NAT both the 10.1.1.0 & the 10.2.2.0 networks as they pass through the router.


Yes this is fine and there should be no problem unless i have misunderstood your topology. The router always keeps a record of the source IP address and port so it will know whether the packet is from 10.1.1.x or 10.2.2.x.


HTH


Jon

bkoum Wed, 07/25/2007 - 11:14

hi Jon


this can work althought the first network pass throught the second? i thought that the packets comes from the first network encapsulated with new frame from the second and it would be impposible to be recognized the ititial ip source....

Correct Answer
Jon Marshall Wed, 07/25/2007 - 11:21

Hi


Can you explain what you mean by first network passes through second.


Where are the routed interfaces for the


10.1.1.0/24 network

10.2.2.0/24 network


IP packets always keep the same source IP unless your are natting but natting does not encapsulate the packet.


If you are tunneling you would be using encapsulation but it doesn't sound from your description as though that is what you are doing.


Jon

bkoum Wed, 07/25/2007 - 11:56

its a fiber optical which connect to lans using sw3550 and after these switches its the router where i want to put the nat and drime me to the internet. the routed interfaces are the Gi interfaces from 3550 switches .

I was thinking that tha packets comes from the network 10.1.1.0 directed throught the 10.2.2.0 at the router changed the ip source addresses from the routing proccess and so the nat would recognize only one network and not the two .

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