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WAN link Bonding


I have a requirement to "bond" two WAN links to be used as a single pipe by the remote site for improved performance at the site.

Current situation:

  • A remote site has two links terminationg on one cisco      2900 router. 1 WAN link to the HQ and another WAN link (from a different      provider) to the DR site.
  • HQ and DR sites are connected to each other via a dark      fiber, currently capped at 10Gbps
  • I have a HQ<>Remote site WAN optimization service      running on Cisco WAAS.

This need has risen because;

  1. more and more applications are getting centralised and      hence hogging more WAN bandwidth
  2. even with optimisation, the utilization for most sites      has shot to over 70%
  3. we have noted that if sometimes assymentric routing      occurs, the optimization serving the remote site doesnt work, probably the      routing breaks the applications sessions or so.
  4. we have the two links on active standby.. (at any time,      this is controlled by EIGRP dynamically based on the metrics).. THIS IS      THE OPORTUNITY as we have idle capacity for the standby bandwidth...

Please do not hesistate to get back for any clarification...Contributions much appreciated.


Super Bronze

Re: WAN link Bonding


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What you want to do is "bond" your two WAN links, per remote, where one runs to main site and one runs to remote site?  Unless, you have something like Ethernet WAN links and have a VSS setup between your main and DR site, "bonding" links isn't likely.

However, assuming your links are routed (as you note using EIGRP), and assuming in a non-DR situation, traffic flows to/from your main site, you can configure link path costing so both the main site "looks" equal to/from a spoke, either direct or via the DR site.

If you equipment supports it, PfR (with PIRO) option would dynamically load balance across the two independent paths even when the routing cost isn't equal (nor is EIGRP variance needed).  (NB: statically equal costing and PfR are not mutually exclusive.)


even with optimisation, the utilization for most sites      has shot to over 70%

"Generic" 70% utilization could be meaningless if you also have QoS.  With real traffic, 30% utilization could be too high and/or 100% is just fine.  It really depends on your mix of traffic and its actual bandwidth needs.  Some traffic needs bandwidth when it needs it, e.g. VoIP bearer.  Other traffic will use whatever is available, including filling a pipe, but only needs enough bandwidth to satisfy a long term need, e.g. bulk data transfers.

WAAS is great when it works, but some traffic just doesn't optimize well.  E.g. encrypted traffic and/or images.


you can configure link path

you can configure link path costing so both the main site "looks" equal to/from a spoke, either direct or via the DR site.

Joseph means tuning the EIGRP metrics (bandwidth or rather delay) so that W1+D=W2 (metrics of WAN1, dark fiber, WAN2).


However, would you still regard the DR site as a DR site if half of the production spoke traffic is constantly flowing through it?