Does a LSA type 3 has 2 functions?

FrankGuthrieFrankGuthrie Member Posts: 245
in CCNP
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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  • EdTheLadEdTheLad Member Posts: 2,111 ■■■■□□□□□□
    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.
    Networking, sometimes i love it, mostly i hate it.Its all about the $$$$
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  • FrankGuthrieFrankGuthrie Member Posts: 245
    Hi Ed, but aren't there 2 types.

    I'f you're in a stub, no summaries are send, but a default route.
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  • networker050184networker050184 Mod Posts: 11,962 Mod
    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.
    An expert is a man who has made all the mistakes which can be made.
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  • FrankGuthrieFrankGuthrie Member Posts: 245
    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?
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  • networker050184networker050184 Mod Posts: 11,962 Mod
    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.
    An expert is a man who has made all the mistakes which can be made.
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  • FrankGuthrieFrankGuthrie Member Posts: 245
    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?
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  • FrankGuthrieFrankGuthrie Member Posts: 245
    You still with me Networker?
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  • networker050184networker050184 Mod Posts: 11,962 Mod
    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.
    An expert is a man who has made all the mistakes which can be made.
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  • FrankGuthrieFrankGuthrie Member Posts: 245
    Hi Network, that might be a good idea. I'll check with GNS3
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  • dmcneil330dmcneil330 Users Awaiting Email Confirmation Posts: 33 ■■□□□□□□□□
    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.
    CCNP: SWITCH[X] ROUTE[] TSHOOT[]
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  • fredrikjjfredrikjj Member Posts: 879
    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.
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  • dmcneil330dmcneil330 Users Awaiting Email Confirmation Posts: 33 ■■□□□□□□□□
    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.
    CCNP: SWITCH[X] ROUTE[] TSHOOT[]
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