Multilink PPP

Answered Question
Mar 30th, 2009

Hi folks -

I am planning to bundle 6 T1's together using Multilink PPP on a Cisco 2821 router. For that, I plan to order 3 dual

WIC's for terminating the 6T1's.

That being said, how is the traffic load balanced over the 6T1's? If the load balancing happens, is it per packet or per destination. The router will have CEF enabled.

All the 6T1's are from the same provider.

Thanks!

I have this problem too.
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Correct Answer by Giuseppe Larosa about 7 years 8 months ago

Hello Kunal,

>> So if a router has to transmit a 100 MB file across a WAN using the 6T1's bundle, and assuming there is no traffic on the bundle, will the 100MB file fragments be sent over the first T1 alone or will the packets be evenly distributed over the 6 T1's?

evenly distributed over member links using a round robin algorithm eventually fragmented with each fragment sent on a different member link.

This is one of the reasons for using multilink ppp

Hope to help

Giuseppe

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Joseph W. Doherty Tue, 03/31/2009 - 04:06

"That being said, how is the traffic load balanced over the 6T1's? If the load balancing happens, is it per packet or per destination. The router will have CEF enabled. "

If you place all the links into a MLPPP bundle, the router will only "see" one link. I.e. L3 load balancing isn't an issue.

MLPPP as it receives packets, should (ideally) send a packet on the first physically available link. Optionally, MLPPP can fragment a packet and send fragments across all physical links.

Packets can arrive out of sequence on the receiving side, and/or MLPPP fragmented, but MLPPP receiver will reconstruct flow before forwarding.

ksarin123_2 Tue, 03/31/2009 - 06:44

So if a router has to transmit a 100 MB file across a WAN using the 6T1's bundle, and assuming there is no traffic on the bundle, will the 100MB file fragments be sent over the first T1 alone or will the packets be evenly distributed over the 6 T1's?

What configuration do I need for this?

"Optionally, MLPPP can fragment a packet and send fragments across all physical links".

Correct Answer
Giuseppe Larosa Tue, 03/31/2009 - 06:54

Hello Kunal,

>> So if a router has to transmit a 100 MB file across a WAN using the 6T1's bundle, and assuming there is no traffic on the bundle, will the 100MB file fragments be sent over the first T1 alone or will the packets be evenly distributed over the 6 T1's?

evenly distributed over member links using a round robin algorithm eventually fragmented with each fragment sent on a different member link.

This is one of the reasons for using multilink ppp

Hope to help

Giuseppe

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