Does a LSA type 3 has 2 functions?

Does a LSA type 3 has 2 functions?

It is used to summarize networks from other area's and send into other area's, unless it's a stub area. But it is also used in stub areas the send a default route (0.0.0.0/0). So it has 2 functions depending on the type of area it's going to be used in, correct?

1. Send default route: 0.0.0.0/0
2. Summarize netwok from other Area's

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Comments

EdTheLad

The question doesn't make sense, a type 3 lsa is a summary lsa generated by the abr to describe type 1 lsa's within the area. Weather or not the abr decides to generate a default type 3 lsa, has nothing to do with type 3 lsa's in general, it has to do with abr behavior.

FrankGuthrie

Hi Ed, but aren't there 2 types.

I'f you're in a stub, no summaries are send, but a default route.

networker050184

Ed's point is that the type 3 LSA containing a default is not a different type than one containing a summary for a normal prefix.

FrankGuthrie

Hi Networker,

Ok, maybe the wording is a bit strange. I know only that there is only the 1 LSA type 3, but isn't there different data in their depending on what kind of area is behind the ABR?

So If there is a stub area, and LSA 3 type is send with an 0.0.0.0/0 route. If there is a normal area behind it, an LSA type 3 is send with a summary of the networks e.g (192.168.1.0/24, 192.168.2.0/24, 192.168.3.0/24, 192.168.4.0/24, 192.168.5.0/24, 192.168.6.0/24, etcc) becomes 192.168.1.0/23?

networker050184

Sure the actual prefix is different, but the prefix 0.0.0.0/0 is carried in the same way 10.0.0.0/8 is carried.

FrankGuthrie

networker050184 wrote: »

Sure the actual prefix is different, but the prefix 0.0.0.0/0 is carried in the same way 10.0.0.0/8 is carried.

Hi networker, what do you mean by that it is caried the same way? Do you mean the LSA type 3 packet format? Basically are you saying only the data (prefix) in the packet is different?

FrankGuthrie

You still with me Networker?

networker050184

Yes, the format is the same as far as I know. Just the prefix carried is different. To be 100% sure you can fire up GNS3 and do a packet capture to compare.

FrankGuthrie

Hi Network, that might be a good idea. I'll check with GNS3

dmcneil330

I replied to your post on CLN similarly. Type 3 LSAs have ONE function with MULTIPLE uses. You are describing 2 uses of the Type 3 LSAs one function: to summarize routes.

fredrikjj

dmcneil330 wrote: »

I replied to your post on CLN similarly. Type 3 LSAs have ONE function with MULTIPLE uses. You are describing 2 uses of the Type 3 LSAs one function: to summarize routes.

No its main function is to hide topology information about other areas from the area where the type 3 is generated. The ability to summarize routes is a byproduct of the ABR taking routing information from its RIB and sending it into the other area in a "distance vector" fashion.

dmcneil330

fredrikjj wrote: »

No its main function is to hide topology information about other areas from the area where the type 3 is generated. The ability to summarize routes is a byproduct of the ABR taking routing information from its RIB and sending it into the other area in a "distance vector" fashion.

correct. I'm sorry. We can argue semantics on that.