[c-nsp] Alternative to AToM Tunnel Select?

Eric Osborne eosborne at cisco.com
Fri Oct 15 15:50:24 EDT 2004

Hash: SHA1

Adam Strawson wrote:
| Hi,
| I have a small scale AToM configuration that uses the "AToM Tunnel
| Select" feature to force a specific path through the network per
| subscriber without any fallback/re-routing.  Specifically we have ..
|   pseudowire-class Path1
|    encapsulation mpls
|    preferred-path interface Tunnel1 disable-fallback
|   !
|   interface Fastethernet0/0.3
|    encapsulation dot1q 3
|    xconnect <IP> <VC ID> pw-class Path1
|   !
|   [where Tunnel1 is built with an explicit path]
| This works well but gives 2 problems that I'm considering before a wider
| scale deployment ...
| 1) The "AToM Tunnel Select" is limited to 12.0S right now that limits
| our PE platform choice [we use 7200s with L2 VLAN handoff via some cheap
| switches today].
| 2) Our NOC would find it easier to manage without the L2 VLAN handoff
| ... so ideally we'd like a solution where we could deploy something like
| the 3750 Metro switch as the PE.
| Does anyone here have ideas [or ideally experience] of building a
| moderately large scale deployment of AToM where each path is explicitly
| configured and failover is disabled without using "AToM tunnel select"
| and/or using a small L3 switch as a PE?  If so, PLEASE point me in the
| right direction!

By "AToM where each path is explicitly configured", do you really mean you want
to steer different AToM VCs along their own individual paths, without regard to
IP shortest cost?  Only way you could do this would involve an ugly set of
static routes.  There's no way to do something other than IP shortest cost
without using TE, modulo static routes which of course are not the most
scalable tool in your toolbox.

Could you do tunnels on the P routers, and just make sure routes to the remote
AToM PE point down explicitly routed tunnels on the P?  This would be less
granular, but therefore less work, than doing it at the PE, and presumably your
Ps are 12.0S.


| Thanks!
| Adam.
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