Multiple DS3 Private Line - Interleaving/LB options?

Unanswered Question

Due to the fact that we have a LEC time interval issue with procuring an optical long-haul Ethernet circuit between our 2 datacenter locations (one in TX and one in AL), we have been forced to migrate to ordering (3) Private Line DS3 circuits.

Equipment: 6513s on each side currently supporting dual-MPLS providers & redistributed routing tables for each.

These circuits will be used for replication of data between our 2 datacenter facilities.


Do we have any options with interleaving the traffic across all 3 of these circuits outside of having any L3 functionality or protocol-based load balancing? (I don't know of anything outside of multipath/multihop/CEF which are not applicable here)

On our existing P2P L2 circuits, we currently have to use manual routing via static route statements and use IP SLA to monitor each side of the links to assist with failover.


Would it be a good design if we had dual 7204VX routers on the inside of ther 6513s that could isolate these links from the remainder of the core IP/MPLS network and we could then have more options with multilinking of these circuits? (IP CEF with per destination load balancing?)

Appreciate the support & thanks!


I have this problem too.
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Giuseppe Larosa Thu, 07/02/2009 - 11:29

Hello Andy,

>> IP CEF with per destination load balancing

This is available also on C6513 running IOS you don't need to deploy C7204VXR for this if you have the right type of linecards:

enhanced flexwan with 2 PA 2T3+

or SIP linecard with the appropriate SPA.

if you haven't the right HW on the C6513 and you don't want to spend money for an interim solution (you are waiting for faster links) you can install the PAs 2T3+ over the C7204.

If you have already the C7204 chassis with enough powerful processor this is clearly attractive.

This kind of design is referred as introducing a WAN/Edge block in campus design that is separated by the core layer.


3 DS3 links fit well in one or three edge routers.

I see that you would like to use two routers to avoid single point of failure.

You could use PBR to put some traffic on the router with a single DS3 link (with increased cost for the protocol in use) on both sides.

This could allow for usage of the links even if two links are on edge1 and only one on edge2.

Using default values the 6513 would send roughly half of the traffic to edge1 and half to edge 2 because it would see two equal cost paths.

Hope to help


Joseph W. Doherty Thu, 07/02/2009 - 19:26

Will the data replication be seen as one src/dest flow or multiple src/dest flows? If the former CEF per-destination might only use one path. CEF per-packet load balancing would much better utilize the 3 links but exposes you to flow sequencing issues. Unknown how well, or whether, 6500 or 7200 might support something like MLPPP for 3 DS3s.


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