EIGRP and NAT

Unanswered Question
Dec 2nd, 2008

Hi,

I have question about NAT and routing NAT-ed address over EIGRP. If i NAT source host on Router A, Router B will see this network as it is and i would like it to learn NAT-ed address so it can return packets for it withaout static routes. Is this posible?

BR

Filip

I have this problem too.
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Jon Marshall Tue, 12/02/2008 - 04:30

Filip

Not clear exactly what you mean. Do you mean you want Router B to see 172.16.200.2 address without having to add a static route for it ?

If so, simplest solution is to create a loopback interface on Router A from same subnet and advertise with EIGRP eg.

Router A

int loopback 10

ip address 172.16.200.1 255.255.255.0

router eigrp 1

network 172.16.200.0 0.0.0.255

Jon

filip_martic Tue, 12/02/2008 - 05:15

Hi Jon,

Yes this is workaroud but if i have more subnets learned on Routera A and they are translated than i would have more Loopback interfaces or class B interface.

for excapmle NAT

10.221.31.231/24 --> 172.16.31.231

10.221.224.9/29 -->172.16.200.3

10.221.224.65/29 -->172.16.200.4

10.221.225.9/29 -->172.16.201.5

10.221.226.65/29 -->172.16.201.6

10.221.46.231/24 -->172.16.46.231

Then i would have to make Loopback Interface with calss B, is there any other way to do it?

BR

Filip

Filip

Jon Marshall Tue, 12/02/2008 - 05:21

Filip

You need to get the Natted IP subnets into the EIGRP routing table. So you can

1) have static route for each subnet on Router A and redistribute into EIGRP

2) As previously suggested - create loopbacks.

Could you perhaps plan your IP addressing of the NAtted subnets so you use just one loopback interface - remember you are never going to be routing to that interface

OR

int loopback 10

ip address 172.16.1.1 255.255.0.0

router eigrp 1

network 172.16.0.0

this would as you say allow you to use any 172.16.x. subnet altho i would recommend using a subset of 172.16.0.0 rather than the whole thing.

Jon

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