2811 with 2 xDSL circuits, NAT and Default route configuration

Unanswered Question
Jul 29th, 2008

I've been asked to setup a 2811 router with 2 DSL connections into an ISP. The customer wants to load balance across the 2 outbound circuits, which I planned to do using 2 equal cost default routes. They also need to NAT/PAT the outbound traffic.

Setting this up on one DSL is no problem. It all starts to go wrong when I add the second DSL. I'm using two Dialer interface's, one bound to each xDSL, as the NAT/PAT source.

Adding a second NAT statement that uses the second dialer as the NAT source breaks the NAT completely, so I'm doing something wrong here. Is this valid, I'm told this should work.

The second issue is to do with default routes, I need to obtain the next hop information from the ISP dynamically, this didnt work as expected either. I tried using the DHCP option on the default route, but ran out time to test this, although it didnt appear to be working.

Any idea's, I'm sure this should work.

I have this problem too.
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Marwan ALshawi Tue, 07/29/2008 - 06:50

about NAT/PAT what i sugist you to do is to divid your internal network to two networks for nating

then with route-map and ACLs match each part of the divided source network

then apply each route map to a nat statment

in this case you gonna load shre the network not exactly loadbalance it with nating

with defould route why u dont use the dialer interface it self as the exit point

because the dsl is pp(point to point )

u can dot like

ip route interface dialer 0

or 1

again with PAT

just likne

ip nat inside source route-map xxx interface dialer0

and the other one with other dialer interface

good luck

aacole Thu, 07/31/2008 - 06:32

Hi, no not yet, I ran out of time whilst on site.

But, one thing I did see, I pointed the default routes out to the dialer interfaces, there are 2, 1 for each dsl interface. checking the ip route table there were 2 DF routes, both dialer interfaces were up even though only one dsl was active. Again, I've not been able to look at this since, am going to set it up a lab.

I've been told that I should be able to configure 2 NAT processes, one per interface, so that bit should have worked.

Marwan ALshawi Thu, 07/31/2008 - 07:52

sure u can have to equal path default routes

but about the nating i am just trying to think about it

reasonably if u have to nating for the same source going to deffrent interfaces

how the router will handel the packet when comes?

there is no round robin or a hashing function even i think no loadbalanceing that if possiable am i right ?

any way i think as i told u divide ur networ to two subnet through ACLs

and make two route maps each one matching one of the ACLs

them make two nating each nate use one of the routes maps and point to deffrent dialer interface


good luck

if u sovle it let me know


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