connect two routers together

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Mar 23rd, 2007
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i have two 2811 with 4 t1s between them. (2 on each). I would like to connect the two f0/1 interfaces on each router to each other so if both t1s go down on one router the packets coming in f0/0 will just route out f0/1 to the other router that still has its t1s up. i have a block of 32 addresses and i can't really subnet them. if i HAAADD to i could but it would mess things up. i wanted to just take another ip address from that range and put it on that router interface. but there would be a route overlap. to get by this could i just add both interfaces to the same bridge group? any other suggestions?

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Overall Rating: 2.7 (3 ratings)
cpembleton Mon, 03/26/2007 - 20:52
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You could configure a rfc 1918 address on the f0/1 interfaces. This will allow the 2 routers to pass traffic. Setup the hop as a backup route or use some other dynamic routing protocol. (OSPF or IBGP).

From your diagram it looks like there is switch connecting your routers F0/0 interfaces. If so you could also use your F0/0 interfaces as they are on the same network so you could have it send the traffic back out f0/0 to the other f0/0 interface.

Hope this helps.


Please rate if it helps!

m.matteson Tue, 03/27/2007 - 08:14
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i would actually also have both f0/1 interfaces connected to a switch too (6513). each f0/1 and f0/0 would be on different modules. say module 12 & 13 of the switch so if it blows up everything still works. i thought about reusing my f0/0 but i would like to have dual physical routes to the internal network just for the sake of physical redundancy as well as a way to load balance. currently i am using RIP. i would like for each router to use both of its T1s + a route to the other router to load balance more equally across all of our bandwidth. i do like the suggestion of rfc 1918 though.

cpembleton Tue, 03/27/2007 - 08:32
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Would recomend you swith to a dynamic routing protocol like ospf or EIGRP. Use ospf if you want to include your ASA in the OSPF process. If not use EIGRP.

You could also use route maps to control the traffic. Our setup multi-links to load balance your T1's.

If your 6513 is behind your firewall I would recomend getting a couple smaller switches to attach your routers and firewall. Always good practice to have physical seperation from external and internal networks.

Hope this helps,


Please rate if this helps!

m.matteson Tue, 03/27/2007 - 08:49
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the 6513 is behind the asa's and also has the fw service module. i would like to keep the asa in the routing process but i could use rip or ospf for that. i could also enable eigrp for the routers to be aware of each other. i forget which one has the lower admin cost. i think it might be eigrp so that would be used instead of any routers learned from the rip process. to simplify things i only showed one asa. but i really have two and both have CSM modules. i don't think i'm familiar with multi-links for the t1s. could you explain?

achalante Tue, 03/27/2007 - 04:42
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Looking at your topology, the best bet would be to use a routing protocol...preferably, you could use eigrp/ospf. With this, you can specify the exact address of an interface into the routing protocol, thus making it easy to monitor the interface should that address no longer exist in the routing table. If you need more information on how to go about this, then reply. thanks.

m.matteson Tue, 03/27/2007 - 08:53
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i'm sort of limited to ospf or rip for the asa. but i could enable eigrp for the routers only since that is primarily where my concern is. the asa's will do per-destination load balancing anyways and there is no way around that. but it would be nice if i could split the traffic from one router to another and actually use all 4. i know a few different ways i could accomplish this but i'm just looking for some advice and input to find the 'best' way. thanks so far for your help!


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