Comments inline with DS
In the past, I've had two routers, with 2 GRE tunnel interfaces each.
DS Where do these tunnels terminate? Just between these two routers?
When one tunnel would go down, EIGRP would instantly converge, and begin passing traffic through the secondary tunnel. I've since moved the secondary tunnel to a second router at each location, and convergence now takes roughly 15 seconds.
DS Does this mean you now have a box of four routers?
A----
B
A'----
B'
Is this due to the fact that multiple neighbor relationships existed between the two routers, and because of this the primary tunnel was able to send a "Goodbye" packet via the secondary tunnel, enabling rapid convergence?
DS. No. EIGRP treats two links between two Routers as independent peers and can't use one link to send info pertaining to the other peer relationship.
As it stands it appears that the 15 second delay is a result of hello / hold timers being exceeded. If this is the case, I'll look into using something like Bidirectional Forwarding Detection; I just wanted to make sure the behavior I'm seeing is expected. I'd like to avoid putting band-aids on something if there is something significantly wrong with the underlying configuration.
DS Apparently the link down is no longer happening or being reported to EIGRP, so you're relying on hold timer expiration. Thats what you need to explore.
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