mohammedmahmoud Tue, 05/08/2007 - 05:48
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Are the public IPs yours, or did you get them from the 2 ISPs, and is there any routing protocols running. Its easy to control the upstream traffic but the issue is how to control the downstream traffic.


Mohammed Mahmoud,

cognize123 Tue, 05/08/2007 - 05:57
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ISP2 is my

Sample scheme

ISP2---My router---ISP1


int et 0/0

ip addr (sample)

int et 0/1

ip addr


ISP1 -

ISP2 -


1ISP is down -> go to ISP2

I am looking for route-map ... but no implement this solution

Thank you

mohammedmahmoud Tue, 05/08/2007 - 06:07
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If you are talking about primary and backup, you should use a static route to the first ISP and a floating static route (a static route with higher AD) to the other ISP, while doing NATing and having your LAN interface as inside and both the ISPs interfaces as NAT outside (and make sure that your Ethernet interfaces have keepalives configured.).

If you need some kind of load sharing, you'll have to NAT some of your LAN IPs to ISP1 and the rest to ISP2, you won't have 50/50 load balancing, but you'll have a decent load sharing.

NOTE: I've assumed that you don't have internal servers that you wish to publish to the internet.

HTH, please do rate if it does help,

Mohammed Mahmoud.

cognize123 Tue, 05/08/2007 - 06:11
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Thank you.

I am think this evening about your post. (be reading books)

sundar.palaniappan Tue, 05/08/2007 - 05:58
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You can designate one ISP connection to be the backup by assigning a higher admin distance for the 2nd static route. You may run into failover problems if you are connecting to the ISP via ethernet due to the nature of the medium. Cisco has a feature called static routing using enhanced object tracking to address this problem.

Have a look at the example and object tracking feature info shown in the links below.

Your config would look something like this;

ip route (ISP1_next_hop)

ip route (ISP2_next_hop) 200 --> you are setting the static route with a higher admin distance. This route would serve as a backup only to the primary default route.



Mohamed Sobair Tue, 05/08/2007 - 06:20
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Hi there,

In addition to Sundar & Mohamed post, If you are looking to loadbalance traffic accross both ISP's as well, you can configure (IP load-sharing per packet)interface command at both interfaces connecting to the ISPs and do the following:

IP route (ISP1 nexthop)

IP route (ISP2 nexthop)

This will do loadbalance your traffic per packet across both ISPs.


cognize123 Tue, 05/08/2007 - 06:24
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Thank you, but i didnt need for load balancing

Only backup route


sorry for my english


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