Want an IP on the physical interfaces within a MLPPP interface

[miked]

I have a Cisco 2811 configured with 2 serial interfaces in a MLPPP interface. This all works fine. What I would like to do is be able to ping each physical interface individually to monitor whether one of the interfaces goes down.

I have done this successfully on a 7206 but with this 2811 I can't seem to get a connected route to come up with an IP directly on the interface.

The set up is like this:

interface Multilink1
description MLPPP Interface
ip address 172.30.1.13 255.255.255.252
no ip redirects
no ip proxy-arp
no cdp enable
ppp multilink
ppp multilink group 1
end

interface Serial0/0/1:0

description T1 #1

ip address 172.30.1.21 255.255.255.252

no ip redirects

no ip unreachables

ip directed-broadcast

no ip proxy-arp

encapsulation ppp

ip mroute-cache

pulse-time 3

no cdp enable

ppp multilink

ppp multilink group 1

interface Serial0/1/0
description T1 #2
ip address 172.30.1.25 255.255.255.252
no ip redirects
no ip unreachables
no ip proxy-arp
encapsulation ppp
no fair-queue
pulse-time 3
service-module t1 clock source internal
service-module t1 timeslots 1-24
no cdp enable
ppp multilink
ppp multilink group 1

The 172.30.1.21 and .25 should come up as connected routes but they don't. It the ability to do this subject to what equipment is used? I wouldn't think so, but this has me guessing.

Any help would be appreciated.

Thanks!

[Richard Burts]

Miked

I am surprised that you got it to work on 7206. Cisco is pretty specific that in configuring Multilink PPP that the IP address goes on the logical interface and not on the physical interfaces. They want to to the IP processing on the logical interface and not on physical interfaces that make up the multilink bundle.

If you want to monitor the physical interfaces you can use SNMP to check interface status. But I do not believe that you would be able to monitor the serial interfaces by ping when they are part of a multilink bundle.

HTH

Rick

[miked]

Thanks for the reply Richard.

Is anyone aware of any documentation regarding this? Since I do have it working on the 7200 any offical info I have to back it up will be helpful.

Just for the record, I'm not trying to really use the physical IP for any "production" type traffic, but just to ping my local side of the serial connection. So the traffic would never tranverse the T1 using these IP's.

Thanks again.

[Richard Burts]

Miked

In fact if you ping your own serial point to point interface IP address in Cisco IOS the ping packet will traverse the serial link. You issue the ping command to ping your own address, the router sends the ping packet out the interface, the ping packet is received by the neighbor device on the point to point circuit, it forwards the packet back to you, and your router recognizes and responds to the ping (and the ping response also goes over the serial link and comes back over the serial link).

If you want to see this you can ping the peer router serial IP and then ping your own serial IP. The response time for pinging your own address should be approximately twice the response time to ping the neighbor address. Or a better demonstration might be this:

- do a show interface on your T1 interface and note the counters for packets in and packets out.

- do a ping with 50 (or some higher number) iterations to your own serial IP address.

- do a show interface of the T1 interface and compare the counters. There should be 2 packets out and 2 packets in for each iteration of the ping.

It may or may not be important in terms of what you are trying to do. But I think it is helpful to understand how things work, and any potential impact of how we do things in the network.

HTH

Rick