type3 LSA and ABR with multiple areas
this is slightly confusing me
I try my best to explain things as clear as possible without attaching complex pictures of the topology but this one is slightly complex.
so the situation is this
on R2 where the big red arrow is. there is an ABR which has interfaces connected to area 0 area 1 and area 2. The network to focus on is 192.168.1.8/30 which all the ABR's in area 2 create a summary lsa to inject into area 0.
I have been doing research into this and this makes sense from a post someone made in a forum.
" OSPF will never transit a non-zero area to get to another non-zero area. The reason is because OSPF doesn't send summary LSA's between non-zero areas directly. They must all be sent to area zero first and then area zero sends them back down to the other areas. So area zero must always be the transit area between 2 non-zero areas. "
So this means R2 injects a type 3 into area 0 and doesn't inject it from area 2 straight into area 1..
so how does this work ? does the type 3 float around in area 0 then come back to R2 then R2 injects the type3 from area zero for 192.168.1.8 at a cost of 10 back into area 1.
I get how R5 has 2 paths. a lower cost path via area 1 and a higher cost path via area 0 and uses area zero as it has to go via the backbone as the transit area to get to another non backbone area.
but R6 goes via R7 through area 1 to get to non backbone area 2 where the 192.168.1.8 network sits. Naturally this makes sense given the lower cost lsa is advertised by R2 but following the above statements logic shouldnt we go via R5 as that leads via area 0 to get to area 2.
sorry for the confusing post but any help would be appreciated.
I try my best to explain things as clear as possible without attaching complex pictures of the topology but this one is slightly complex.
so the situation is this
on R2 where the big red arrow is. there is an ABR which has interfaces connected to area 0 area 1 and area 2. The network to focus on is 192.168.1.8/30 which all the ABR's in area 2 create a summary lsa to inject into area 0.
I have been doing research into this and this makes sense from a post someone made in a forum.
" OSPF will never transit a non-zero area to get to another non-zero area. The reason is because OSPF doesn't send summary LSA's between non-zero areas directly. They must all be sent to area zero first and then area zero sends them back down to the other areas. So area zero must always be the transit area between 2 non-zero areas. "
So this means R2 injects a type 3 into area 0 and doesn't inject it from area 2 straight into area 1..
so how does this work ? does the type 3 float around in area 0 then come back to R2 then R2 injects the type3 from area zero for 192.168.1.8 at a cost of 10 back into area 1.
I get how R5 has 2 paths. a lower cost path via area 1 and a higher cost path via area 0 and uses area zero as it has to go via the backbone as the transit area to get to another non backbone area.
but R6 goes via R7 through area 1 to get to non backbone area 2 where the 192.168.1.8 network sits. Naturally this makes sense given the lower cost lsa is advertised by R2 but following the above statements logic shouldnt we go via R5 as that leads via area 0 to get to area 2.
sorry for the confusing post but any help would be appreciated.
_____________________________________
CCNP ROUTE - passed 20/3/12
CCNP SWITCH - passed 25/10/12
CCNP TSHOOT - passed 11/12/12
CCNP ROUTE - passed 20/3/12
CCNP SWITCH - passed 25/10/12
CCNP TSHOOT - passed 11/12/12
Comments
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networker050184
Mod Posts: 11,962 Mod
There is nothing wrong with R6 going via R7 because they are in the same area.
The rule doesn't allow a router in area 1 to go through area 2 for example. But traffic can route to either abr in its area.An expert is a man who has made all the mistakes which can be made.