Area range not-advertise command !

[illusion_rox]

hi all, if we use area range x.x.x.x y.y.y.y not-advertise command on ABR, it will filter type 1 lsa to be originated as type 3 in the attatched non backbone area, what is the reason behind it ? can some one tell me where is it defined in the ospfv2 RFC ?, and also correct me in my assumption that RFC tell us all !! i mean cisco and other vendors follow RFC to implement protocols so every action or result we see from our configuration shouldnt it be defined in the RFC somewhere ?

Kindly guide me

[Giuseppe Larosa]

Hello Ovais,

that command is a way to implement a route filter at area boundary.

If you want create an aggregate a summarized route and you want it to be advertised just remove the not-advertise option.

About RFC for OSPFv2 look at RFC2328

List of area address ranges

In order to aggregate routing information at area boundaries,

area address ranges can be employed. Each address range is

specified by an [address,mask] pair and a status indication of

either Advertise or DoNotAdvertise (see Section 12.4.3).

When the

range's status indicates DoNotAdvertise, the Type 3

summary-LSA is suppressed and the component networks

remain hidden from other areas.

So this is a standard behaviour

Hope to help

Giuseppe

[Richard Burts]

Ovais

This is an excellent response from Giuseppe and worth the rating that I give it.

I would like to address this part of your post:

"and also correct me in my assumption that RFC tell us all".

I do not think that it is true that the RFC tells us all. The RFC gives a common basis on which different vendors implement something (like OSPF). The RFC specifies things that the protocol should do and sometimes specifies things that the protocol should not do. The vendor should follow the directives provided in the RFC. But the vendor is not limited to only the things directed in the RFC. Many vendors will implement proprietary extensions to the protocol. So there may very well be parts of your config that are not something defined in the RFC but are provided by the vendor who wants to go above and beyond the specifics of the RFC to make it work better.

HTH

Rick

[Asif Ali]

Hi 

Can we hide summary route for any particular area instead of all other areas

[Giuseppe Larosa]

Hello Asif,

you can achieve the desired behaviour by using a more modern approach/command supported in IOS that is the area <area-id> filter-list <route-map-name> in.

See

https://www.cisco.com/c/m/en_us/techdoc/dc/reference/cli/nxos/commands/ospf/area-filter-list-ospf.html

>> Use the area filter-list command to filter Type 3 LSAs. If you apply the route map with the in keyword, the route map filters all Type 3 LSAs originated by the ABR to this area, including Type 3 LSAs that originated as a result of the area range command in another area. 

You can use a prefix-list to specify what is passed to the area (permitted by the prefix-list) and what is filtered (denied by the prefix-list )

See the following example of usage:

https://www.netcraftsmen.com/filtering-ospf-areas-in-ospf/

Hope to help

Giuseppe