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Community Member

EIGRP and Virtual-access interfaces


I'm building an SGBP solution for branch backup and have been

experimenting with virtual-template/virtual access interfaces and seen

some truly bizarre results.

To put it simply, I have a branch with two routers. One is normally

connected back to the 'core' over 128K Kilostream and the other has an

ISDN BRI. The normal routing protocol is EIGRP, everything in the same

AS. If the Kilostream fails floating static routes on both branch

routers point the routes back to the core out of the ISDN BRI on the

second router, which brings up an ISDN connection to a PRI on the


I've had this working with Multichassis Multilink PPP using 'Legacy'

configs on the core physical interfaces, because allegedly SGBP

doesn't support Dialer Profiles.

I've tried replacing the 'Legacy' configs with a virtual-template

setup, which initially worked fine. If I shut down the serial lines to

the branches they dial in as normal, a virtual-access interface is

built, routes are properly injected (using RIP summaries on the ISDN).

The problem is when I bring back up the serial connections. The EIGRP

neighbour relationships over the serial links don't get rebuilt, so

the normal EIGRP routes don't replace the floating statics, the ISDN

is therefore not torn down. Even when I physically unplugged the

branch ISDNs the floating statics stay valid.

It appears that when the serial link is restored, it is somehow

bundled into the virtual-access interface, even though it's from a

different branch router than the ISDN connection. Only by killing the

core router's 'Virtual-profile virtual-template 1" command and

clearing the virtual-access interfaces could I persuade the EIGRP

neighbour relationships to reform on the serial links. Freaky!

Apologies for the length of this post but if anyone has read this far

can anyone advise if this is normal? Are the serial links somehow

considered associated with the virtual-access interfaces because the

same routes are visible over both?

Grateful for any advice.



Community Member

Re: EIGRP and Virtual-access interfaces

As it turns out the answer is painfully obvious.

Bringing back up the serial line actually creates a new virtual access interface, which since it's cloned from the config intended for ISDN, isn't properly configured for the serial line. I hadn't anticipated the SGBP/virtual profile configuration affecting the serial links, but they are PPP, so it does kind of make sense.

Just adding the "virtual-profile if-needed" command seems to fix it.



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