[c-nsp] TE design guidance

[Oliver Boehmer (oboehmer)]

Justin Shore <> wrote on Monday, August 06, 2007 11:43 PM:

> I'm trying to come up with the best way to layout TE tunnels between a
> couple POPs.  On one side I have a pair of 7600s with 3BXLs running
> SRB1; we'll call this A and B.  On the other side I have a pair of
> ME6524s; we'll call these C and D.  Each pair of routers serves are
> the core in their respective POP, with the edge devices dual-homing
> to each core router.  The first router in each POP is connected via
> GigE over about 80 miles of fiber through numerous towns using media
> converters. The second router in each POP is connected in a similar
> fashion over another strand in the same fiber bundle.  A 3rd
> connection is being made with radios and will terminate in the first
> router in each POP.  At some point in the future the second fiber
> path will be broken in the middle to drop off services in that town. 
> I anticipate either a 7201 or another 7600 depending on bandwidth
> needs vs costs; we'll call this future router E.
> 
> My short term needs mainly involve FRR.  However as our backbone
> bandwidth needs grow we'll likely need the full set of TE features in
> the not-too-distant long-term.
> 
> Unfortunately we do not have 2 diverse fiber paths to work with at
> this point in time.  My initial thought was that I should build
> tunnels for A-C, B-D, A-B-D-C, and B-A-C-D.  However the radios
> complicate that design in my eyes.  How do I indicate that the radio
> path is more costly than the fiber path for as far as MPLS TE is
> concerned?  Do I need an explicit path defined for each possible
> combination of paths?  Am I simply not looking at this in the right
> light? 

Well, it really depends on how you want A and B to route the traffic to
C and D. Guess you need to build a full mesh of tunnels (i.e. A-C, A-D,
B-C, B-D, and reverse), and you use a dynamic path option, the tunnels
should follow the shortest IGP path through your network. Then you use
autoroute to steer the traffic over the tunnels, and enable LDP on the
tunnel if you need to send tagged traffic over them.

If you're only worried about FRR at this time, I'd signal the tunnel
with "bandwidth 1". With appropriately high IGP metrics on the radio
link, this setup will not use the Radio link (unless it's the only one
left), so you might need to create another tunnel over this path (using
explicit path option). However, you need to tell how you want this link
to be used..

Then you enable backup tunnels to protect links and/or nodes, and you're
all set.

Guess you really need to figure out how the traffic between the pops
should be distributed along the paths, and configure the tunnels
accordingly. If you can't use dynamic, a loose-hop explicit path can
also achieve the desired results.

	oli