Routing problem with my ISP please help!

Unanswered Question
Jul 17th, 2007


I have a pool of IP address to reach my ISP

ip route

ip route

ip route

ip route

ip route

all of them are FR conecctions.

1. How can I make load balancing between all my interfaces? because when I use only one static route evrything works ok, but if I add the second and the third it doesn't work.

all my interfaces are configured like this:

description Circuito 8151-0012462

bandwidth 1920

ip address

encapsulation frame-relay IETF

no ip mroute-cache

load-interval 30

serial restart-delay 0


frame-relay interface-dlci 516

frame-relay lmi-type ansi

there is not IP address problems etc, is a matter of routing do I have a NAT or any special configuration on my router to make it work?




I have this problem too.
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Paolo Bevilacqua Tue, 07/17/2007 - 13:27

Yes, unless you have BGP with your own AS, you need NAT to load balance over all these connections. If this is acceptable for you, decide how you want to "partition" your internal address to go out and use the different connections. If all the address can use all the exit interfaces, just configure the same nat statement like

"ip nat source inside list 101 interface x/y.z overload" multiple times in addition to "ip nat inside" and "ip nat outside" and the access-list 101 that defines traffic to be natted.

Hope this helps, please rate post if it does!

Leonardo A Pena... Tue, 07/17/2007 - 13:31

Hi bevilaqua thanks for your reply can you give an specific nat example of how can I do it please

Richard Burts Tue, 07/17/2007 - 13:50


My first thought was also that NAT/PAT was needed. But in the original post Leo says that when using a single address/single route that everything works ok. If it works ok out a single interface how could it be a NAT/PAT issue?

Perhaps Leo can give us some additional details about the addressing plan used in his network and how that relates to the addressing of his provider.



Paolo Bevilacqua Tue, 07/17/2007 - 13:58

Well, it may be that he has another NAT device behind the router, so when it goes out of "right" interface it works, but not with the others.

Definitely more details are needed as it seems peculiar one has that many interfaces and is not clear if to the same or different ISPs.

Leonardo A Pena... Wed, 07/18/2007 - 05:15

Well is only one ISP.

I mean when I use one static route to acces tne internet I have no problem but If I add a second one it doesn't work properly.

I do not have any device doing NAT. I get all my conection FR from ISP directly to my router. The ip address on my serial interfaces have mask /30.

My goal is to be able to route the internet traffic over my 5 serial interfaces with my 5 static routes.

Thank a lot


Richard Burts Wed, 07/18/2007 - 05:49

Perhaps you can clarify a bit about what is happening. When you say that a single static route works fine, is it a particular static route that you are using, or are you saying that if you use the first one by itself it is fine, or if you use the second one by itself it is fine, or if you use the third one by itself it is fine, and so on?



Leonardo A Pena... Wed, 07/18/2007 - 06:02

exactly rburst if I use the first one by itself it is fine, the second one by itself it is fine, and so on, but when I try to use more than one at the same time it becomes slow and I loose the connection to the internet.


with a single static route (It could be any of five FR)I have no problem

ip route

But adding a second one

ip route

ip route



Then It doesn't work


Richard Burts Wed, 07/18/2007 - 06:24

Well that is a very strange situation. When you have two static routes like that it should put outbound traffic on both. Normally that would not be a problem. Are you doing anything on your router that would cause per packet load sharing? I wonder if the provider could be doing some kind of stateful inspection that would have a problem with assymetric traffic?




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