design for redundant outbound connection

[woongko]

Hi,
we have leased one T1 point-to-point to our main office with 1720 router on both ends. This connection is very critical and we need to set up standby outbound line to the main office. We considered to add secondary T1 interface to the 1720. But because secondary T1 is coming from same ISP, it didn't look good for redundancy. We also considered to get DSL from different ISP, add DSL interface to the 1720, and set up VPN to main office through DSL interface. Then T1 and DSL interface can backup each other residing on same router. I am new to Cisco configuration and not sure the second scenario is even possible technically. I'd appreciate any suggestion. Thanks.

Dave

 

[voltron1011]

Yes you can add a second T-1, since the 1720 has two WICs. Once you have the second T-1 you'll be able to load ballance the two T-1's. You can use EIGRP to load ballance the two links.

 

[JOAMON]

The main thing to consider when talking about redundancy is that in order for it to be truly redundant then the copper into the building must come from differnet manholes and terminate at seperate CO's with different ISP's. Otherwise if all the copper for both T1 and DSL come into the building from the same manhole and terminate at the same CO then if the fiber sekking backhoe digs up the copper truck then you still lose everything and if the CO has issues then you could lose it all as well. We only have one copper path to our building and only one possible CO to terminate into. So we chose to go with two T1 lines bonded together in a Multilink PPP bundle giving us 3 meg of bandwidth. While this is not redundant in that since is does have some redundancy in thatf one T1 line fails the circuit does not go down it just looses 50% of it's bandwidth. We have over the course of time lost one of the two for brief periods and to the best of my knowledge have never totally lost connection. If all of the copper runs into your building in the same manner as ours then you may want to see if there is a wireless provider in your area that can provide a failover backup method for you.

 

[KiscoKid]

Your second scenario is very possible. You should however consider 2 routers if redundancy is important to you

 

[voltron1011]

Yes, redundancy can get expensive really quickly. It all depends on what kind of organization you are with. You have to weigh out the pros and cons of how much redundancy you want. Since you mention low end 1720 routers, I assume that you are a smaller company.

 

[woongko]

I decided not to have two T1s from same ISP(JOAMON, I am aware of that but still you raised a good point....). Can you guys help me what I may need?
I think I need to get VPN module and DSL WIC for currently active 1720 router. I've read about loadbalancing two T1s with multilink or EIGRP but not sure how to configure loadbalancing with T1(dedicated point-to-point) and DSL from two different ISPs. Any advice or help is very much appraciated.
Thanks,
Dave