said by lildevil:
They are different AS's.
A and B 65001
A and C 65002
B and D 65003
I would assume the following
* A and B are within AS 65001
* A and B speak iBGP to each other
* C is within AS 65002
* D is within AS 65003
* A and C speak eBGP to each other
* B and D speak eBGP to each other
* Those BGP ASes are not sub ASes
With those in mind, typically you can consider either Active/Passive scenario or Active/Active scenario. Active/Passive scenario is when (let's say) A to C is Primary link to reach 10.10.10.0/24 while B to D is Backup link. When there are multiple networks or subnets within AS 65001, then you could set A to C as Primary link to some subnets and set B to D as Primary link to some other subnets.
Note that the above solution will use eBGP relationship among ASes. As nosx
mentioned, you cannot use the IGP metric redistribution into BGP as decision maker of choosing path selection between multiple BGP AS talking eBGP since IGP metric only concerns its local BGP AS and is not advertised outside local AS.
Just think of this way. If there are multiple BGP AS talking eBGP to each other, they should only deal (or care) with eBGP communication. There is no IGP between these ASes to talk with. Therefore why should any outside BGP AS care or deal with some IGP within some BGP AS?