Router with NAT and multiple WAN circuits

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Aug 3rd, 2007
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Hello Everyone,

We have a router in one of our offices that has a T1 as it's primary Internet connection and is doing PAT using overloading (using the serial0/1/0 interface address).

A new fractional T1 was installed in another serial (serial0/2/0 interface for their backup internet connection and I'm having a problem with NAT when users go out this interface.

My configuration looks like this.

access-list 10 permit

access-list 20 permit

ip nat inside source list 10 interface s0/1/0 overload

ip nat inside source list 20 interface s0/2/0 overload

int s0/1/0

desc main internet link

ip nat outside

int fa0/0

desc backup internet link

ip nat inside

ip route s0/1/0

ip route s0/2/0 10

I tried using ACL 10 for both overload statements but it did not work so I made 2 ACLS that are identical so I can have both overload statements in the config.

I have a feeling that when the router is trying to do nat, it is still using the first overload statement (for s0/1/0).

Could someone please help me with this config? Do I need a route map or something? This office does not care about their source IP address on the Internet since no external DNS is considered so PAT is fine.

Thanks for the help.


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Overall Rating: 3 (1 ratings)
Collin Clark Fri, 08/03/2007 - 10:10
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You're missing some items.

int s0/2/0

ip nat outside

You could do a NAT debug and see what it is doing.

HTH and please rate.

priedman1 Fri, 08/03/2007 - 10:50
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Thanks for pointing that out. I missed that in my post but did have in my configuration.


ankbhasi Fri, 08/03/2007 - 10:11
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Hi Pete,

Can you try calling PBR in your NAT statement and see if that helps you.

Something like this

ip route s0/1/0

ip route s0/2/0 10


ip nat inside source route-map interface s0/1/0 overload

ip nat inside source route-map interface s0/2/0 overload


route-map permit 10

match interface s0/1/0


route-map permit 10

match interface s0/2/0

Try the same and update if it worked for you.



watson.daniel Tue, 09/04/2007 - 00:00
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I have had the same issue and I was calling the routemaps in my nat overload statement. I am logging TAC case for config assistance so hopefully this will be fixable, certainly a lot easier on an ASA.

Paolo Bevilacqua Tue, 09/04/2007 - 03:52
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yes it is using s0/1/0 because the corresponding default route has a lower administrative distance (0 vs. 10). If you make the routes having the same weight, traffic should pseudo-balance over the two links.


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