[c-nsp] backup quandry

Charles Sprickman spork at inch.com
Wed Oct 20 16:49:10 EDT 2004


I've been trying to come up with a decent plan to offer backup circuits to
customers that works well.  We have something of an odd environment here
and most of the solutions I've run through fall short in one way or

This is a cheap-o backup solution.  The scenario is that the client has a
Covad "Telextend" T1 with the backup line being a Covad SDSL.  I'm aware
that this offers no protection against Covad going wonky.  We generally
see that most of our client outages are due to Verizon mucking about with
things, so it actually works quite well.

On the client side we're using Netopia gear and it handles cutting over
the outbound traffic well.

To handle routing the client LAN block to SDSL and ADSL circuits, I enable
OAM management on the pvcs and add two static routes to the interfaces
(one with lower priority).  If one of the circuits fails, the route to
that pvc gets yanked as OAM lets us get interface up/down status.

The problem is with the "T1" circuits.  Covad brings these into T1 cards
in their DSLAMs and the does a frame<->ATM translation there.  Sadly they
don't configure the DSLAM to handle any of the ATM OAM stuff for these
circuits, so from my router I have no way of getting the status of the T1

First off, any suggestions for the above scenario?  I need some way to
determine if the T1 is up or not, but since it's a virtual circuit and
Covad does not support the standard signalling, I don't think there's
anything I can do there.

Second question, Covad has recently approved the Cisco 17xx series routers
for the Telextend service.  With one of those in place, I could run OSPF
over the T1 and put the SDSL router in bridge mode and also run OSPF over
that link.  The only problem there is that the T1 is a 1.5 Mb/s line and
the SDSL backup link is generally going to be a lower speed link so I
don't want to "balance" the two lines, I want the SDSL to only be used if
the T1 is down.  What other options am I missing to make this happen?  I'm
open to all sorts of nutty hackish ideas...



Charles Sprickman
spork at inch.com

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