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New Member

DMVPN and EIGRP metric

Hello.

In a DMVPN lab I have one Hub router and two Spokes. The DMVPN is working properly. Routing works, spokes see each other, tunnel protection works. The problem I'm facing is the following.

Besides the DMVPN, the hub router and spoke1 have a direct serial link. Now, when spoke1 tries to connect to spoke2, it goes through that direct serial link through the hub.

Tracing this, it looks like even the tunnel has "ip no next-hop-self eigrp x" on the hub, it is advertising to spoke1 its own metric instead of the AD the hub gets from spoke2.

What would be the best to avoid this, and make the hub advertise the AD from spoke2 to spoke1?

7 REPLIES

Re: DMVPN and EIGRP metric

set bandwidth and delay on the tunnel interface to correct the metrics.

New Member

Re: DMVPN and EIGRP metric

Thanks, Alekseev.

It worked for a single cloud DMVPN.

However, in a dual cloud DMVPN configuration where the two hub routers are connected back to back, it still doesn't work.

Following your adviced also for the dual cloud DMVPN, I tried several combinations, none of which gave optimal routing results.

Routes for spoke2 get announced over hub2 to hub1, instead of going directly through the tunnel; either that, or routes from spoke1 to the net behind the hub routers go through the DMVPN instead of the non-shared direct link.

Hall of Fame Super Silver

Re: DMVPN and EIGRP metric

Hello Octavio,

a)

you say "Tracing this, it looks like even the tunnel has "ip no next-hop-self eigrp x" on the hub, it is advertising to spoke1 its own metric instead of the AD the hub gets from spoke2.

What would be the best to avoid this, and make the hub advertise the AD from spoke2 to spoke1?"

I don't think you can make this for the way that EIGRP works: it cannot advertise the received metric to somebody else.It advertise as its own AD its best metric to the route. (DV behaviour)

However, you can play with several tools to manipulate metric on different tunnel and physical interfaces

interface BW and delay, 'distribute-list…',

'offset-list…'

In this way you can have control what hub is preferred to reach a specific subnet or you can build a hierarchy of hubs.

However, for dual Hub dual DMVPN clouds be aware that there is a restriction:

Spoke-spoke dynamic tunnels can be setup only within same DMVPN

So if spoke1 and spoke2 haven't a common hub they cannot build a direct spoke-to-spoke tunnel.

b)

When you say:

"Besides the DMVPN, the hub router and spoke1 have a direct serial link. Now, when spoke1 tries to connect to spoke2, it goes through that direct serial link through the hub."

DMVPN builds a virtual backbone over a real network. So serial interface can be part of the real physical backbone and used to carry tunnel packets to and from spoke1 and hub.

But in the physical backbone you need to use a different routing protocol (at least a different process) with the only objective to make the public addresses reachable and NHRP mapping of virtual backbone ip addresses to the real ip addresses possible.

You shouldn't mix the two networks this could break the security level provided by the ipsec+mGRE overheads.

Hope to help

Giuseppe

Re: DMVPN and EIGRP metric

could you show the lab topoloigy?

New Member

Re: DMVPN and EIGRP metric

Alekseev: sure.

http://alvarezp.ods.org/dmvpn-serial/

There are two diagrams.

One is the physical diagram, with the central router representing the public Internet. H1 = Hub1. S1 = Spoke1. CORP = Corporate net.

The other one is the virtual diagram, where each DMVPN is represented as an ethernet link.

IP addressing is supposed to be as simple as possible.

This is the relevant output part for show ip eigrp topology 10.20.0.0/16 on S1. The total delay S1 is getting for 10.20.0.0/16 is false.

S1#show ip eigrp topology 10.20.0.0/16

IP-EIGRP (AS 1): Topology entry for 10.20.0.0/16

State is Passive, Query origin flag is 1, 1 Successor(s), FD is 5890560

Routing Descriptor Blocks:

192.168.0.2 (Serial0/1), from 192.168.0.2, Send flag is 0x0

Vector metric:

Total delay is 175000 microseconds

172.16.2.12 (Tunnel2), from 172.16.2.1, Send flag is 0x0

Vector metric:

Total delay is 185000 microseconds

172.16.1.12 (Tunnel1), from 172.16.1.1, Send flag is 0x0

Vector metric:

Total delay is 185000 microseconds

Hall of Fame Super Silver

Re: DMVPN and EIGRP metric

Hello Octavio,

may you post output of show ip eigrp interface for tunnel1, tunnel2, ser0/1 on spoke S1 and HUB H1 ?

is the path via ser0/1 the preferred one ?

FD is 5890560

With default k-values

bw component is the inverse of the smallest BW in the path in kbps

256 * 10^7 / 2048 = 1250000

256 * 10^7 / 1536 = 1666667

Delay component is cumulative and in 10s of microseconds

256 * (Sum of all delays in the path| in 10s of microsec)

Hope to help

Giuseppe

New Member

Re: DMVPN and EIGRP metric

Here is the output for "show ip eigrp interface" for the four routers involved in the tunnel.

http://pastebin.com/f36b834cb

> is the path via ser0/1 the preferred one ?

If you mean, administratively, yes, it is the preferred one for S1 to get to the corporate network, but not to get to other spokes.

For the rest of your comment, I didn't quite follow it. Those are the calculations, but I didn't understand what did you try to tell me. Sorry.

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