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New Member

Which routing protocol?

Looking for routing protocol suggestion.

My network currently has two routers, we'll call them Router A and Router B for the moment. Router A is the default gateway for traffic to the internet with Router B being the backup gateway.

The connection that I am concerned with is the connection to a remote office. Occasionaly, the latency for the connection between the default Gateway and the remote office will jump to about 5 times the usual. However, the backup router's latency will still remain as normal. Both routers' connections are being routed through IP Tunnels. I want to use a routing protocol, on Router A, which will recognise the difference in latency and redirect traffic through the Router B tunnel.

Therefore, I am asking for advice as to which routing protocol I can use that will use latency as a metric as opposed to the current metric of hop count, because being routed through a tunnel, the hop count is only 1 hop.

Hopefully I have explained my query in a manner that is understandable.

thanks in advance for any advice.

1 ACCEPTED SOLUTION

Accepted Solutions
Gold

Re: Which routing protocol?

It wouldn't help, since the protocols don't support routing based on latency. What you might want to look at is optimized edge routing, OER, an upcoming feature in IOS. I'm also going to talk to the EIGRP developers to see if we can get this going as something to talk about again.

Russ.W

15 REPLIES
New Member

Re: Which routing protocol?

EIGRP supports link latency (delay) as a routing metric. I am not sure that implementing it will solve your problem, though. You should investigate the reasons for latency increase you experience. If it is caused by occassional surges of traffic, then using latency as routing metric will not help you, because you will redirect traffic to the backup router, which in turns will get saturated by traffic and latency will increase; then the routing protocol will direct the traffic back to primary router and so on.

New Member

Re: Which routing protocol?

I'm not sure how to try and identify the the reasons for latency. I am just assuming that there is a problem somewhere in the internet "cloud" that is causing the latency.

New Member

Re: Which routing protocol?

I assumed the latency is between the gateway router and your remote office (ie. on your own LAN/WAN). If the latency is in the Internet, then no routing protocol is going to help you (you don't run EIGRP on the Internet...)

New Member

Re: Which routing protocol?

I must apologise due to the fact that I am still a trainee and still in the process of learning, therefore I'm not too great at explaining things yet.

Basically the connection is through an IP tunnel over the internet using tunneling protocol GRE/IP. What I want is a solution in which router A recognises the fact that when latency jumps, the path through the tunnel is higher than normal and then to use router B's tunnel as at this point it becomes the quickest route.

New Member

Re: Which routing protocol?

Aha. Well, if you run EIGRP through the tunnel, it should become aware of the latency over the tunnel, so this might actually work. I haven't tried anything like this, though.

New Member

Re: Which routing protocol?

ok, I'll give it a bash and see what happens. thanks

Gold

Re: Which routing protocol?

EIGRP does not dynamically adjust its routes based on the delays across interfaces, primarily because every time anyone has tried turning this on, it causes too much churn in the network. Instead, EIGRP pulls the configured delay off the interface when it is first configured on the interfaces, and leaves it there throughout its operations.

Russ.W

New Member

Re: Which routing protocol?

So do you have any other suggestions, russ? I suppose the phrase "dynamically adjust" is the kind of thing I'm looking for. I need the router to dynamically adjust what interface it sends traffic to depending on latency to the remote office. Is it possible?

Gold

Re: Which routing protocol?

Not at layer 3.... I think you could do something like this with MPLS/TE, but I'm not even certain it will pay attention to the dynamic load and delay counters on the interface. :-( There might be some layer 2 way to do this, but I don't know about it. I'll ask someone else to take a look, and see if they have any ideas for you from a layer 2 perspective.

Russ.W

Gold

Re: Which routing protocol?

Okay, I checked with one of the layer two folks around here (Steve Moore, he's actually a routing protocols guy, but he used to be on the WAN Team in the TAC, so he's our "layer 2 guy" on the team :-) ), and he said there's no way he knows of, either. :-(

Maybe it's time to open this coversation again with the EIGRP coders, to see if we can get this working.

Russ.W

New Member

Re: Which routing protocol?

Hmmm, somehow I was under impression that EIGRP uses its own RTT measurments (those one can see in "show ip eigrp neighbors" ... I was wrong.

Gold

Re: Which routing protocol?

Actually, that's the one measurement you wouldn't want to use for this. :-) The actual load and delay counters under the interface are fairly accurate, given they are based on all the traffic out the interface. The RTT counter in EIGRP is based only on the time it takes to get an ack for a EIGRP packet, and it can vary wildly--especially if there are very few reliable EIGRP packets passing through the link for some time.

For instance, if you bring up a bunch of EIGRP neighbors on a single ethernet, and then look at their RTO's from each router's point of view, you'll often find some of them have low RTO's, which others have high RTO's, for no apparent reason (they are on the same link, so you would think they'd be consistent, but they aren't).

By setting the K values, you can theoretically get EIGRP to pay attention to the load and delay values on the interface, but we only read those values when the bandwidth changes, and since the bandwidth is manually configured, well.... It kindof defeats the entire purpose of carrying those things in EIGRP, doesn't it. :-) Maybe we'll get into some big discussion about this again someday, and figure out some way to fix it....

:-)

Russ.W

New Member

Re: Which routing protocol?

First of all, I'd like to thank you guys for trying to help out. When I was first asked to solve this problem, I didn't think it would be too hard, just do some research into a few routing protocols and see what comes up. Hasn't quite worked like that, it's now looking like an impossibility as far as I can see. Maybe it could be included in a new type of routing protocol??

Anyway, I'll report back to my IT colleagues with disappointing news. Thanks for the effort guys.

New Member

Re: Which routing protocol?

Or....what about adding a third router which is placed before Router A and Router B, then it can decide which is the best path?

Gold

Re: Which routing protocol?

It wouldn't help, since the protocols don't support routing based on latency. What you might want to look at is optimized edge routing, OER, an upcoming feature in IOS. I'm also going to talk to the EIGRP developers to see if we can get this going as something to talk about again.

Russ.W

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