How Is The Forwarding Address decided?
See the link above for my topology. All links are P2P and R4 is redistributing the 126.96.36.199 prefix into OSPF.
I want to know how the forwarding address is decided for any external routes that R4 redistributes into OSPF? Currently R3 is the type 7 to 5 translator.
R1#sh ip ospf database external 188.8.131.52
OSPF Router with ID (184.108.40.206) (Process ID 1)
Type-5 AS External Link States
Routing Bit Set on this LSA
LS age: 1012
Options: (No TOS-capability, DC)
LS Type: AS External Link
Link State ID: 220.127.116.11 (External Network Number )
Advertising Router: 18.104.22.168
LS Seq Number: 80000005
Network Mask: /24
Metric Type: 2 (Larger than any link state path)
Forward Address: 10.0.24.4
External Route Tag: 0
And I can see that R4 has set the forward address to 10.0.24.4. I don't understand why? If I look on R4 I can see, from the output below, that he also has an ospf enabled interface on fa0/0 with a higher IP address. So I expected to see that 10.0.34.4 (as it's a higher value) would be forwarding address. But that's not the case here and I can't understand why?
R4#sh ip ospf int brief
Interface PID Area IP Address/Mask Cost State Nbrs F/C
Fa0/1 1 1 10.0.24.4/24 10 P2P 1/1
Fa0/0 1 1 10.0.34.4/24 10 P2P 1/1
I also don't understand Cisco's website on this forwarding address. The website says that for the forward address to be set to a non-zero value that the "ASBR's next hop interface is not point-to-point". Yet I have a P2P network only here and the forward address is not zero.
FYI If I do actually turn the NSSA into a broadcast network, I do get the desired behaviour. Where the forward address changes to 10.0.34.4 instead.