Policy based routing example

Unanswered Question
May 11th, 2008

Hi

At present I have one central router where 2 line is connected . one of ISP (A) is connected to internet and other is connected to Branch office. Now all net realted data www, smptp, ftp are go through ISP (A).

I want to do:

Now another ISP (B) is connected my router. I want from specific IP or Proxy IP address request www through ISP 3 and rest of data smtp, ftp ,others rquest process via ISP 2. But if any of ISP line A or B is down then all data pass alive ISP and when two ISP is come back normal then data request previous condition.

I think anyone help me full fill this sceniro with the example.

thanks

Biplob

I have this problem too.
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izackvail Sun, 05/11/2008 - 15:06

Hi Biplob, you could use an access list to match the type of traffic that you are wanting to policy route and then a set command to point it at the next hop ISP that you want. This would work best if you were running some kind of a dynamic routing protocol because if the next hop you specify goes down the router will ignore the route map and route the packet normally.

For example:

access-list 101 permit tcp any any eq www

route-map NEXT_HOP

match ip address 101

set ip next-hop 10.1.1.1

int f0/0

ip policy route-map NEXT-HOP

You could also try using the set interface command. You could do something like:

route-map NEXT_HOP

match ip address 101

set interface serial0 serial1 serial2

The router will use the first available interface in the list.

iqbalkhan Mon, 05/12/2008 - 22:34

Hi

I mistype .correction is regarding ISP A B C=

Hi

At present I have one central router where 2 line is connected . one of ISP (A) is connected to internet and other ISP (B) is connected to Branch office. Now all net realted data www, smptp, ftp are go through ISP (A).

I want to do:

Now another ISP (c) is connected my router. I want from specific IP or Proxy IP address request www through ISP C and rest of data smtp, ftp ,others rquest process via ISP A. But if any of ISP line A or C is down then all data pass alive ISP and when two ISP is come back normal then data request previous condition.

iqbalkhan Mon, 05/12/2008 - 22:42

Hi IZA

Thanks your example.

in your example you shows permit all IP.

BUT if if I permit from specific IP request www through ISP C then just change the ACL.

like if my pc IP is 203.113.178.5 and next hop is 10.1.1.1

then I just edit:

access-list 101 permit tcp any 203.113.178.5 eq www

route-map NEXT_HOP

match ip address 101

set ip next-hop 10.1.1.1

Pls let me know

thanks

biplob

izackvail Tue, 05/13/2008 - 05:17

Hi Biplob, it looks like you are on the right track except that access-list would route anything destined for 203.113.178.5. I think you want anything sourced from 203.113.178.5 with a desination port of 80 don't you? That would look like this:

access-list 101 permit tcp 203.113.178.5 any eq www

Either way I think you have the right idea.

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