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Beginner
Beginner

Multilink PPP

Hi all,

I have 2 2811 routers with 4 T1 lines connecting them, I would like to use multilink. I have a few questions before I get started:

1. will there be downtime when I switch to multilink? or will traffic continue to pass thru?

2. Is creating a traffic class and policy manditory?

thank you

8 REPLIES 8
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Hall of Fame Guru

Nasir

There may be a brief interruption of traffic as you make the config changes to implement multilink (removing the IP address from the serial, assigning the serial to the multilink group, etc). How much interruption will also be affected by how well you coordinate the changes on both ends. But if you have your changes planned and can just paste the config changes into the config from a text file the interruption should be very small.

traffic class and policy may be desirable (depending on your environment) but they are not mandatory for using multilink.

HTH

Rick

HTH

Rick
Highlighted

Thanks for your response.

I have created the following configs: can you or anyone else see anything there that might give me problems when i apply it?

config of router A:

interface Multilink1

ip address 10.82.163.2 255.255.255.252

ppp multilink

ppp multilink-group 1

!

interface Serial0/0/0

description Connection to

bandwidth 1544

ip unnumbered FastEthernet0/1

ip accounting output-packets

no ip mroute-cache

no fair-queue

ppp multilink

multilink-group 1

!

interface Serial0/1/0

description Connection to

bandwidth 1544

ip unnumbered FastEthernet0/1

ip accounting output-packets

no ip mroute-cache

no fair-queue

ppp multilink

multilink-group 1

no shut

!

interface Serial0/2/0

description Connection to

bandwidth 1544

ip unnumbered FastEthernet0/1

ip accounting output-packets

no ip mroute-cache

no fair-queue

ppp multilink

multilink-group 1

no shut

!

interface Serial0/3/0

description Connection to

bandwidth 1544

ip unnumbered FastEthernet0/1

ip accounting output-packets

no ip mroute-cache

no fair-queue

ppp multilink

multilink-group 1

no shut

!

Config of router B:

interface Multilink1

ip address 10.82.163.1 255.255.255.252

ppp multilink

ppp multilink-group 1

!

interface Serial0/0/0

description Connection to

bandwidth 1544

ip unnumbered FastEthernet0/1

ip accounting output-packets

no ip mroute-cache

no fair-queue

ppp multilink

multilink-group 1

!

interface Serial0/1/0

description Connection to

bandwidth 1544

ip unnumbered FastEthernet0/1

ip accounting output-packets

no ip mroute-cache

no fair-queue

ppp multilink

multilink-group 1

no shut

!

interface Serial0/2/0

description Connection to

bandwidth 1544

ip unnumbered FastEthernet0/1

ip accounting output-packets

no ip mroute-cache

no fair-queue

ppp multilink

multilink-group 1

no shut

!

interface Serial0/3/0

description Connection to

bandwidth 1544

ip unnumbered FastEthernet0/1

ip accounting output-packets

no ip mroute-cache

no fair-queue

ppp multilink

multilink-group 1

no shut

!

once again thanks for the very useful info.

Highlighted

The main thing that I notice in your suggested config is that you are specifying ip unnumbered and ip accounting on the serial interfaces. When you configure multilink the multilink interface is the layer 3 interface which gets things like ip address and accounting (if desired) and the serial interfaces should not have these.

The original post asked about potential downtime when configuring multilink. This leads me to believe that the serial interfaces are already in use. How are they currently configured? That might have some affect on what you need to change as you go to multilink.

HTH

Rick

HTH

Rick
Highlighted

currently only 1 serial interface is active, we will soon be getting 3 additional T1 lines. In my configuration I just added the multilink commands to the interfaces.

Also, are you saying that I should remove ip unnumbered and ip accounting from the serial interfaces and place them on the multilink interface?

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on the multilink bundle, int multilink 1;

enter

ppp multilink fragment disable

this will prevent fragmentation of induvidual frames @ Layer 2. this usually causes issues with anything but ping from working... so use it!

Highlighted

currently we use "ip authenication" for eigrp at the serial interface, shoul I apply that to the multilink interface or keep it at the serial interface?

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As a rule of thumb when you create a virtual interface, like multilink interface, most/all of your layer 3 config should be configured under that int. With that said you need to configure the 'ip authentication' under the multilink int.

HTH,

Sundar

*Please rate all helpful posts.

Highlighted

Nasir

Sundar has said it well: most layer 3 parameters should be configured on the multilink and not on the physical serial interfaces. So to be explicit, yes you should remove the ip unnumbered and ip accounting from the serial interfaces. The ip authentication should go on the multilink.

HTH

Rick

HTH

Rick