This topic is to discuss the following lesson:
Could you clarify the differences between this and OSPFv3 Prefix Suppression?
I believe the main difference is that type 8’s and 9’s are suppressed rather than type 1 or 2’s.
Are stub’s advertised as /128’s?
Also how does OSPF detect that a prefix is part of a transit network?
In OSPFv3, there is no prefix information in LSA type 1 and 2 anymore, you can find those in LSA type 8 and 9 so yes, OSPFv3 prefix suppression removes it from LSA type 8 and 9.
About the prefix / transit network. Here’s a quick example with three routers connected like this:
All routers are in area 0 and R3 is the DR:
R3#show ipv6 ospf database prefix self-originate OSPFv3 Router with ID (18.104.22.168) (Process ID 1) Intra Area Prefix Link States (Area 0) LS age: 8 LS Type: Intra-Area-Prefix-LSA Link State ID: 0 Advertising Router: 22.214.171.124 LS Seq Number: 80000002 Checksum: 0x7834 Length: 52 Referenced LSA Type: 2001 Referenced Link State ID: 0 Referenced Advertising Router: 126.96.36.199 Number of Prefixes: 1 Prefix Address: 2001:DB8:3333:3333::3 Prefix Length: 128, Options: LA, Metric: 0 LS age: 1729 LS Type: Intra-Area-Prefix-LSA Link State ID: 3072 Advertising Router: 188.8.131.52 LS Seq Number: 80000001 Checksum: 0x16FD Length: 44 Referenced LSA Type: 2002 Referenced Link State ID: 3 Referenced Advertising Router: 184.108.40.206 Number of Prefixes: 1 Prefix Address: 2001:23:23:23:: Prefix Length: 64, Options: None, Metric: 0
Above you can see the referenced LSA type:
* 2001: Associated with the router
* 2002: Associated with the Network LSA
The 2001:23:23:23:: prefix is configured on an Ethernet network, thus it shows up with LSA type 2002. You can also see the link state ID (3) of the advertising router (R3 our DR).
R3#show ipv6 ospf database network self-originate OSPFv3 Router with ID (220.127.116.11) (Process ID 1) Net Link States (Area 0) LS age: 426 Options: (V6-Bit, E-Bit, R-Bit, DC-Bit) LS Type: Network Links Link State ID: 3 (Interface ID of Designated Router) Advertising Router: 18.104.22.168 LS Seq Number: 80000002 Checksum: 0x41A3 Length: 32 Attached Router: 22.214.171.124 Attached Router: 126.96.36.199
About the stub, you mean a stub network? Loopbacks are advertised with a /128, similar to how OSPFv2 advertises them as a /32 by default.
Hi Rene ,
Can explain a bit about how the how ospf detect transit links when performing ospf prefix suppression . Also, you are mentioning that /32 link is considered an invalid link in the lsdb.In such case why aren’ t the Loopback networks considered invalid when prefix suppression is enabled? These are also /32 links.
There are two types of LSAs that we have to deal with in this lesson: The Router LSA, that is a type 1 LSA that contains prefix information about the 192.168.30.0/24 network, and the Network LSA< that is a type 2 LSA that contains prefix information about the 192.168.123.0/24 subnet.
If you notice, in each of the LSAs described, the only networks that have a prefix other than /32 are the transit networks, so if you suppress prefixes, the transit networks will be removed.
A subnet mask of /32 on a multi-access network is not possible because then it would not be a multi-access network. So if an OSPF router sees this, it knows that prefix suppression has been applied. It is not invalid in the sense that it cannot exist in the database.
I hope this has been helpful!