Two T1 Lines for a 2811??

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Oct 21st, 2008
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Hi,


I want to install another WIC and another T1 line into our 2811 routers so that we can have two T1 lines between our offices. We currently have one T1 line, but we have an application that consumes the bandwidth, so we would like to install a second T1 line to give the app its own T1 line. So we will add a second WIC to each 2811.


Now for the fun part. How would I setup the routing in the routers to accommodate this? We have two offices, NY & GA. NY uses a 192.168.110.0/24 subnet and GA uses a 192.168.120.0/24 subnet. The T1 line between the two offices is on a 10.1.2.0/24


Here is the sh ip route from NY router:


S 192.168.120.0/24 [1/0] via 10.1.2.2

C 192.168.110.0/24 is directly connected, FastEthernet0/1

10.0.0.0/8 is variably subnetted, 2 subnets, 2 masks

C 10.1.2.0/24 is directly connected, Serial0/0/0

C 10.1.2.2/32 is directly connected, Serial0/0/0

C 192.168.0.0/24 is directly connected, FastEthernet0/0

S 192.168.1.0/24 [1/0] via 10.1.2.2

S* 0.0.0.0/0 [1/0] via 192.168.0.2


What we want to do is have the application, which resides at 192.168.110.12, to only use the new second WIC. So therefore, all traffic that comes from 110.12 will go to the second WIC down to GA to 192.168.120.4


and therefore, of course, vice versa. All traffic coming from 120.4 will go over the second WIC to 110.12


Thanks so much.


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Edison Ortiz Tue, 10/21/2008 - 10:10
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You want source-based routing and this can only be accomplished with PBR (Policy Based Routing).


You need to match the host at the ingress interface in 192.168.110.0/24 and set this host next-hop to be the remote router's secondary WIC.


The return traffic will be the same.


interface fx/x

description 192.168.110.0/24 subnet

ip policy route-map NY->GA


access-list 101 permit ip host 192.168.110.12 192.168.120.0 0.0.0.255


route-map permit NY->GA

match ip address 101

set ip next-hop [ip address of the neighbor's 2nd WIC)



In the remote router:


interface fx/x

description 192.168.120.0/24 subnet

ip policy route-map GA->NY


access-list 101 permit ip 192.168.120.0 0.0.0.255 host 192.168.110.12


route-map permit NY->GA

match ip address 101

set ip next-hop [ip address of the neighbor's 2nd WIC)


HTH,


__


Edison.




jlcarey1usa Tue, 10/21/2008 - 10:22
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OK. That makes sense to me. I will try it out once we get the second T1 line in place.



Are the source and destination always the same? i.e., source = 192.168.110.2 destination = 192.168.120.4


If it is and these are the only two machines that communicate, a regular static route will work and you won't have to use policy routing. Your route will specify the next hop on each router as being the other end of the T1 on both sides.


Since workstations on both sides have a gateway all their own, with no next hop routing in between to get to the destination, then policy routing is not necessary.

Richard Burts Wed, 10/22/2008 - 10:17
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James


I have implemented things like you describe several times and Policy Based Routing works fine. I would suggest a slight refinement in the approach suggested by Edison. Set up routing between the routers to use both T1s and to make 1 T1 primary and the other backup (if you use static routes it would be a higher Administrative Distance on the backup T1 or if you use dymanic routing do something to make the metric some worse on the backup (perhaps with an offset list)). Then configure Policy Based Routing as suggested by Edison. This will allow you to fail over to the second T1 is there is a problem on the first and to keep your application traffic separate as long as both T1s are operational.


HTH


Rick

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