[AusNOG] Multi-path route maps

Joseph Goldman joe at apcs.com.au
Mon Dec 2 13:54:49 EST 2013

Hi Josh,

  1st definition you theorised.

  Basic example:

    Cheap link, poor quality but lots of bandwidth being the Primary path.

    More expensive, great quality link with limited bandwidth being the 
secondary path.

    All traffic by default comes in and out by Primary path.

    I want to set unencrypted web traffic only (For example) to use 
secondary path. Would set route-map to identify TCP port 80 and change 
next-hop. But for these connections only (i.e. the traffic for 
retrieving the website assets) I would like to go back DOWN the 2nd path 
also. So only traffic coming from that 2nd path go back that 2nd path.

Let me know if you'd like any more info :).

Got some off list replies to head me in some directions, but would love 
to hear from anyone who has more knowledge to offer :)


On 02/12/13 13:37, Joshua D'Alton wrote:
> So I think I understand, you want some traffic to go OUT via 2nd link, 
> then be forced to come BACK via 2nd link? And all other traffic via 
> the 1st link? (Or at least you don't care if other traffic comes back 
> via 2nd link too, just so long as THIS specific traffic only uses the 
> 2nd link)?
> On Mon, Dec 2, 2013 at 10:46 AM, Joseph Goldman <joe at apcs.com.au 
> <mailto:joe at apcs.com.au>> wrote:
>     Hi List,
>      In a project of ours we currently have 2 alternate paths between
>     2 points of our own network.
>      We wish to use route-maps to send certain traffic via the
>     alternate path, which is a fairly trivial task, however we would
>     like suggestions on a method to ensure the traffic is sent back
>     via the alternate path.
>      The default routes etc are all via primary path. The IP's are
>     public routed IP's, so a traditional NAT table with alternate
>     public IP won't be of assistance, and as we are trying to do this
>     protocol based we can't change the route for these single IP's.
>      External routing to the internet will all arrive back at this
>     router, we just need to control the route based on the source path
>     used.
>      I believe this will be achieved with some form of different NAT
>     table. The 2 links both deliver between a single pair of Cisco
>     C3900's. I would appreciate if anyone who has accomplished such a
>     thing to push me in the right direction of the feature name etc
>     that I should be looking at.
>     Thanks,
>     Joe
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