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New Member

Routing a remote office through a backup connection help...


At our school, our district office is on a point to point wireless connection that at the moment is un-reliable and dropping packets due to interference (we think). All of the traffic from this office crosses this wireless link (internet, VOIP, and other general network traffic). We are putting in a comcast cable connection at this office soon and are wondering how to use this as a backup for all traffic (internet/voice, etc...). We have a Catalyst 3560 (layer 3 capable image I think) over there already. We just installed a 2801 Router there as well intending to use the SRST function to roll voice over to POTS lines when the wireless is down. The main question is here...HOW do we failover to this backup connection (cable internet) when traffic over the wireless is bad? Is it possible to failover using ACLs? Like if a certain amount or percentage of packets are dropping, the connection could then failover? We are running RIP v.2 as our routing protocol. Any ideas at all would be appreciated. The 3560 switch is: WS-C3560-24PS-S, this IOS version: 12.2(25)SEE3, with this switch image: 3560-IPBASE-M

Thanks for your help!

Hall of Fame Super Silver

Re: Routing a remote office through a backup connection help...

Hello Daniel,

first of all to use an internet connection you need to build an IPSec tunnel for security and routing reasons.

the C2801 can handle the ipsec tunnel.

you can use a GRE tunnel that is carried inside IPSEc packets.

the GRE tunnel provides the advantage that can be used as outgoing interface for routing or even to run a routing protocol over it.

you can use RIP over the tunnel and you can adjust the metric so that is used as a backup link (just a worse metric)

see the example it is for eIGRP but you can adapt it to RIP easily

you need to use the offset-list concept to increase the metric over the tunnel

router rip

version 2

no auto-summary


offset-list 11 in 3 tunnel 5

access-list 11 permit


the offset list must be used on both ends of the GRE tunnel so that routing uses the wireless link when available in both directions.

you need to make the 2801 and the c3560 to talk RIP between them

Hope to help


New Member

Re: Routing a remote office through a backup connection help...


thanks for the reply! Just to clarify, we have the 2801 and the Catalyst 3560 both in one closet in this building. At this point in time, I'm not sure what device would make up the other end of the tunnel in our network. Right now we have a sonic wall device there that may or may not speak RIP very well. Though RIP is not proprietary. We are looking at upgrading our URL filter device right now which throws another iron in the fire so to speak. I guess I was just wondering if we could direct all traffic to the C. 3560 which connects up to our wireless radio. And then if traffic degrades to a certain point, we could then route it to this comcast connection (which by the way will be using an OLD sonic wall device as well).

Hall of Fame Super Silver

Re: Routing a remote office through a backup connection help...

Hello Daniel,

ok the 2801 is in the central building.

However, you need some form of tunneling to be able to use an internet access as a backup link.

You probably mean you would use a form of WEB vpn of SSL VPN. It is probably possible.

What you cannot do is to react on wireless link degradation you need a feature to react when RIP fails.

It can be a form of floating static route.

You probably need to add some othe device in the picture.

You can think of using PPTP between two windows PCs or something like that.

Hope to help


New Member

Re: Routing a remote office through a backup connection help...

I hear what you are saying. Actually, the 2801 and the 3506 are both in the Remote building location. At current time all phones and machines plug into the PoE 3506. The floating static route is something I had thought of as I touched on this in a CCNA lab. The issue is, I don't believe RIP routes will completely disappear. the wireless is unreliable for voice data...packets drops, though I'm pretty sure the routing table would not lose routes to the core network. The link never goes totally down. Which is the reason I was wondering if a failover could happen when the link begins dropping packets.

Super Bronze

Re: Routing a remote office through a backup connection help...

One technology that could reroute based on poor performance, not complete path failure, is Cisco's OER/PfR. However, don't believe it's available on tha 3560. The 2801 should support it but it might require an advanced IOS feature set. Also, at the moment, believe only static or BGP routing supported.

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