Setting advertisement / split horizon direction in EIGRP routing

Question

Hello all,
I am trying to work out if I am being a bit rubbish or if split horizon is my new worst enemy.
Below is a diagram of my (simplified) problem scenario using EIGRP.
The solution I am looking for is that Router R3 learns of the 10.0.0.0/8 network from both R1 and R2, then does not advertise it to either. Simple with split horizon enabled.
But when either R1 or R2 are rebooted, a decision somehow takes place, and may well determine that R3 should advertise 10/8 to the new (rebooted) neighbour, at which point split horizon prevents it from being advertised back again. This means the topology table on R3 doesn't contain this route for this neighbour and is slow to converge if the other neighbour is lost.
Is there a way to control in which direction routes are advertised first on a neighbour link? and then I can let split horizon do its thing
Or is there something I am not thinking of...
many thanks,
Paul

Answer 1

This is what i think would work.
Two assuptions i'm making -
1)  R1 and R2 have full routes in terms of the remote branch subnets which from what we have talked about seems to be the case.
2) R1 will advertise the specific subnets it is primary for (see below) to R3 which then advertises them to R2 and R2 will do the same for it's primary subnets.
R1 is primary for 32 - 63 summary address 192.168.32.0 255.255.224.0
R2 is primary for 64 - 95 summary address 192.168.64.0 255.255.224.0
Each router is secondary for the other router's primary subnets.
on R1 configure a summary address for R2's subnets on the interface connecting to R3 -
ip summary-address eigrp <AS no> 192.168.64.0 255.255.224.0
on R2 do the same for R1's subnets -
ip summary-address eigrp <AS no> 192.168.32.0 255.255.224.0
So now -
R1 points to R3 and R3 points to R2 for 192.168.32.0/19
R2 points to R3 and R3 points to R1 for 192.168.64.0/19
Because you have used a summary address this suppresses the advertisement of the more specific routes within that summary range.
R1 will therefore advertises it's specific subnets for which it is primary to R3 and a summary address only for R2's subnets.
And R2 does the same ie. it advertises it's specific subnets and a summary for R1's.
R3 then obviously passes these summaries via EIGRP to R1 and R2.
R3's routing table will have specific branch routes pointing to the respective
primary router but only a summary route for the same subnets pointing to the secondary router.
Because a router will always pick the longest match it will use the more specific subnets unless there isn't a matching route.
Which means no need to use metrics to load balance traffic.
In addition the summary route is already in the routing table so no need for either R1 or R2 to send a query to R3 if one of their branch links fail.
I may well have overlooked something so let me know whether you think this will work for you or not.
Jon