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New Member

bonding a new t-1 line to existing t-1 line

Hello,

We have a new T-1 being installed and we need to know how to 'bond' this t-1 with our existing T-1 line across two 2610 devices (our WAN link). Any help, advise or suggestions greatly welcome.

TIA,

Gary

5 REPLIES

Re: bonding a new t-1 line to existing t-1 line

Hello,

you can use multilink PPP for this purpose. Be aware that you will loose connectivity while reconfiguring your existing and the new WAN line. The final config can look like this:

interface Multilink1

ip address 10.1.1.1 255.255.255.252

ppp multilink

multilink-group 1

!

interface Serial0

description first T1

no ip address

encapsulation ppp

no ip mroute-cache

no fair-queue

ppp multilink

multilink-group 1

interface Serial2

description second T1

no ip address

encapsulation ppp

no ip mroute-cache

no fair-queue

ppp multilink

multilink-group 1

You need to adjust interface naming and IP addresses to your environment. Make sure both ends are configured appropriately.

Hope this helps! Please rate all posts.

regards, Martin

Re: bonding a new t-1 line to existing t-1 line

Hi Gary,

As Martin suggested, Multilink would be the way to go if you want to achieve true loadbalance between the 2 links.

However i would like to know the interface on the router where the T1 is terminating.

The above configurations may require a slight change accordingly.

Narayan

New Member

Re: bonding a new t-1 line to existing t-1 line

Hi Martin,

Multilink looks a cool option. But i always had this question about Multilinking.

Does this kind of a config fragment every packet and send each of the two fragments across the two links ? If it is going to fragment/re-assemble every packet then ,

1> is it not a 'delay-inducing' mechanism ? and

2> is it not router cpu/memory intensive ?

Could we not actually use something like cef per-packet loadbalancing for specific routes using SBR (eg. route maps).

suggestions please ..

regards

arav

Gold

Re: bonding a new t-1 line to existing t-1 line

Yes the 2 issues you mentioned need to be considered. The fragement size can be configured on PPP to reduce this issue but it and the load just for the encapsulation do exist.

That said PPP does a better job of load balancing than cef per-packet so it is a trade off.

The other thing to think about is delay in the lines. Many times when I have done this the vendor always delivererd 2 new lines. They claimed it was easier than tring to engineer the second line on the exact same path as the first. PPP is not as tolerant of having the lines at different delay. This is anothr concideration to take into account when chooseing your load balance method.

I think the primary reason many people run PPP is that this is mulivendor supported where cef is cisco only. When you control both ends of the lines you can do what you want. When you are buying a connection to a managed servers like internet or MPLS the vendor may insist on using PPP even when thy have cisco equipment.

Re: bonding a new t-1 line to existing t-1 line

Hello,

as already mentioned there might be delay related issues, if both lines differ significantly. But then with CEF per packet you will get packet reordering issues, which are much worse for VoIP afaik.

You could instead use CEF per destination, but this would limit a single connection to T1 speed.

So again I would go for the MLPPP solution. If you find unacceptable issues you can still try CEF per packet load sharing.

As also mentioned I just gave the basic MLPPP configuration, and there are further optional commands for fine tuning. For a full description you can f.e. take a look at "Configuring Media-Independent PPP and Multilink PPP"

http://www.cisco.com/en/US/products/sw/iosswrel/ps1835/products_configuration_guide_chapter09186a00804f2079.html

and at "Using Multilink PPP over Serial Interface Links"

http://www.cisco.com/en/US/products/ps6350/products_configuration_guide_chapter09186a00804a40f9.html

The last link is part of the QoS configuration guide also addressing delay and jitter issues.

Hope this helps! Please rate all posts.

Regards, Martin

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