Try making the routes across the links doubly-recursive. I don't know
how well this works, but it is worth a try. For example:
RTRA-Loopback0 IP 10.1.0.1/30
RTRA-Loopback1 IP 10.1.1.1/30
RTRA-Loopback11 IP 10.1.11.1/30
RTRB-Loopback1 IP 10.2.0.2/30
RTRB-Loopback1 IP 10.2.1.2/30
RTRB-Loopback1 IP 10.2.11.2/30
Then route to one loopback over 4-6 E1's and the other over the other
4-6 E1s
Then, route the Loopback 11s over the two loopbacks. Again, I don't
know if this would work, but it just popped into my head.
Example Config
RTRA
int loopback 0
ip address 10.1.0.1 255.255.255.252
!
int loopback 1
ip address 10.1.1.1 255.255.255.252
!
int loopback 11
ip address 10.1.11.1 255.255.255.252
!
int s0
ip address 192.168.0.1 255.255.255.252
!
int s1
ip address 192.168.1.1 255.255.255.252
!
<snip>
int s11
ip address 192.168.11.1 255.255.255.252
<snip>
! The first 6 E1s
ip route 10.2.0.0 255.255.255.252 192.168.0.2
ip route 10.2.0.0 255.255.255.252 192.168.1.2
ip route 10.2.0.0 255.255.255.252 192.168.2.2
ip route 10.2.0.0 255.255.255.252 192.168.3.2
ip route 10.2.0.0 255.255.255.252 192.168.4.2
ip route 10.2.0.0 255.255.255.252 192.168.5.2
! The other E1s
ip route 10.2.1.0 255.255.255.252 192.168.10.2
ip route 10.2.1.0 255.255.255.252 192.168.11.2
ip route 10.2.1.0 255.255.255.252 192.168.12.2
ip route 10.2.1.0 255.255.255.252 192.168.13.2
ip route 10.2.1.0 255.255.255.252 192.168.14.2
ip route 10.2.1.0 255.255.255.252 192.168.15.2
!
ip route 10.2.11.0 255.255.255.252 10.2.0.2
ip route 10.2.11.0 255.255.255.252 10.2.1.2
!
ip route 172.16.16.0 255.240.0.0 null 0
!
router bgp 65555
neighbor 10.2.11.2 remote-as 65554
network 172.16.16.0 mask 255.240.0.0
Of course, you may have to process-switch the packets, or use CEF, which
you mentioned.
-Chris