https://www.flickr.com/photos/117689526@N08/12594740014/
I'm interested in the subnet 10.108.1.0/24, which is the point-to-point link between R8 and R10. This prefix will be summarized from area 3 into the backbone as a type 3 lsa. R3 will receive the type 3 lsa in area 0 and advertise it as a type 3 lsa to area 4.
So both R2 and R4 in area 1 will have a type 3 lsa which was advertised by R3 for prefix 10.108.1.0/24.
Since R2 has a virtual-link to R3, R2 will also have a type 3 lsa in area 0 advertised by R8.
R2's preferred path is via the VL
R2# sh ip route 10.108.1.0
Routing entry for 10.108.1.0/24
Known via "ospf 1", distance 110, metric 40, type inter area
Last update from 10.24.1.4 on Ethernet0/1, 02:24:42 ago
Routing Descriptor Blocks:
* 10.24.1.4, from 8.8.8.8, 02:24:42 ago, via Ethernet0/1
Route metric is 40, traffic share count is 1
R2#sh ip ospf database summary 10.108.1.0
OSPF Router with ID (2.2.2.2) (Process ID 1)
Summary Net Link States (Area 0)
Routing Bit Set on this LSA in topology Base with MTID 0
LS age: 2 (DoNotAge)
Options: (No TOS-capability, DC, Upward)
LS Type: Summary Links(Network)
Link State ID: 10.108.1.0 (summary Network Number)
Advertising Router: 8.8.8.8
LS Seq Number: 80000001
Checksum: 0x5A41
Length: 28
Network Mask: /24
MTID: 0 Metric: 10
Summary Net Link States (Area 1)
LS age: 484
Options: (No TOS-capability, DC, Upward)
LS Type: Summary Links(Network)
Link State ID: 10.108.1.0 (summary Network Number)
Advertising Router: 3.3.3.3
LS Seq Number: 80000001
Checksum: 0x5550
Length: 28
Network Mask: /24
MTID: 0 Metric: 20
Now since R2 is a backbone router, i expect it to advertise all summaries to any attached area's. R2 is an ABR for area's 0,2 and 1. So i expect the prefix to be advertised to routers R1 in area 2 and R3,R4 in area 1.
R1#sh ip ospf database summary 10.108.1.0
OSPF Router with ID (1.1.1.1) (Process ID 1)
Summary Net Link States (Area 2)
Routing Bit Set on this LSA in topology Base with MTID 0
LS age: 1227
Options: (No TOS-capability, DC, Upward)
LS Type: Summary Links(Network)
Link State ID: 10.108.1.0 (summary Network Number)
Advertising Router: 2.2.2.2
LS Seq Number: 80000005
Checksum: 0x345D
Length: 28
Network Mask: /24
MTID: 0 Metric: 40
R4#sh ip ospf database summary 10.108.1.0
OSPF Router with ID (4.4.4.4) (Process ID 1)
Summary Net Link States (Area 1)
Routing Bit Set on this LSA in topology Base with MTID 0
LS age: 900
Options: (No TOS-capability, DC, Upward)
LS Type: Summary Links(Network)
Link State ID: 10.108.1.0 (summary Network Number)
Advertising Router: 3.3.3.3
LS Seq Number: 80000001
Checksum: 0x5550
Length: 28
Network Mask: /24
MTID: 0 Metric: 20
R4#
The summary from R2 is not being received on R4, it is just seeing the summary from R3.
Is there a rule for virtual links to say "don't advertise backbone summaries into the virtual link transit area"? It makes sense not to, but i haven't seen this rule anywhere.
