Backup Link

[rodrigocas]

I'm trying to configure two Point to Point links that if one of them goes offline the other take its place. What kind of routing protocol you recomend?

Those links will both finish in a router 831 in the branch side and 3745 in the HQ Side.

[mmorris11]

If they are serial T1s then I would recommend MPPP:

http://www.cisco.com/en/US/customer/tech/tk713/tk507/technologies_configuration_example09186a00800a3b85.shtml

[sundar.palaniappan]

Hi,

All the dynamic routing protocols or floating static route are capable of providing redundancy. There are many more options available to provide redundancy like MLPPP, which is a good choice. But, if you are uninterested in it and want to choose a routing protocol then EIGRP would be my recommendation.

It better suits your network setup than the other two widely used IGPs, RIP & OSPF, because of some of the following advantages.

1. Easy to implement & Less complex - easier than OSPF

2. Faster reconvergence - mcuh faster than RIP

3. Not bandwidth intensive - uses much less bandwidth than RIP does to exchange routing updates.

4. Not processor intensive - when compared to OSPF which can consume lot of CPU cycles during SPF calculcation.

There are mechanisms available with RIP that can mitigate the problems associated with legacy RIP but I would still go with EIGRP.

Hope that helps!

Regards,

Sundar

[kradjesh13]

Hi palaniappan,

As you say that the dynamic or floating static routing can provide redundancy, and its not happening in my case.

The site router is configured for DSL as its primary link and ISDN as the secondary link. For primary EIGRP is being used as the routing protocal and for Backup i an using the Floating static with the higher administrative distance.

But the problem is, when ever the primary link goes down, the site gets seperated and nothing is happening. When the primary comes up the site can be accessed.

When i use show ISDN status and Show ISDN history i can see the call is established for particular amount of time. I double checked static routing which i assigned for both the routers seems to be fine. But the traffic is not passing through.

Do you have any idea why this happens??? Hope you will be comming up with some thing that will be helping me.

Thanks

Rajesh Krishanmurthy

[sundar.palaniappan]

Rajesh,

You expressed your desire to use EIGRP as the routing protocol across both your WAN connections and that should be fine. This would solve your problem of the route not failing over to the backup ISDN link when DSL line is down. I hope you don't mind the ISDN link staying up for EIGRP adjacency to be maintained.

I assume the reason why the route didn't failover to the backup ISDN link is because the floating static route via ISDN wouldn't come into the routing table if the primary interface via DSL did not go down. Since, the DSL interface is probably connected to a DSL modem/bridge the ethernet interface wouldn't have gone down but the DSL line wasn't actually usable because the problem was beyond the DSL modem. To address this problem Cisco has a solution called static route using object tracking which would help the router detect problems on the connection like yours. The following link should enlighten you on this topic. If you are interested you can pursue this route.

http://www.cisco.com/en/US/products/sw/iosswrel/ps5413/products_feature_guide09186a00801d862d.html

Good Luck!

Regards,

Sundar

[mchoo2005]

In addition to the previous poster's view on why EIGRP is the better choice for you: the last time I used 800 series routers, I found (in hard way) that they don't support OSPF. So there you go, EIGRP is it then. :)

[ilya.varlashkin]

Since both links terminate on the same router at each site, simply put them into MPPP bundle then you don't need to worry about routing convergence at all.

[rodrigocas]

I think i'm going to use EIGRP because both links ends in an ethernet port. I'm not sure but MPPP it's for BRI links. Am I right?

[ilya.varlashkin]

Ehrm...I thought by point-to-point you ment serial links.

Surely if you have ethernet links than you can't use PPP (btw, it's not only for BRI). If remote site is simple stub network (i.e. there's nothing behind it), there's hardly any value in EIGRP (but it's cool), while adding complexity and extra thing that can break. In your situation static routes will be sufficient as long as your links go down if they break.

[Richard Burts]

I had assumed like Ilya that when Rodrigo said point to point links that he intended some type of serial link. If they do terminate on Ethernet the multilink is not much of an option. If we knew more about the topology and the requirements we might give more specific answer (we do not yet know if the two links are equal cost links, and do not know if they want load sharing on both links or want one to be primary and the other to be backup). But given the amount of information that we currently have I agree that EIGRP would be my first choice.

as far as Rajesh attempt to insert his problem into this discussion, if he can supply some details of the topology, of how EIGRP was configured and of how the floating static was configured we might be able to give helpful answers. It could also be helpful if he started a new thread to discuss his particular situation.

HTH

Rick

[rameshwarhiwale]

do multilink ppp or icrease the one of the metrics.