09-09-2007 10:08 PM - edited 03-03-2019 06:40 PM
Hi all,
When OSPF routers are connected in numbered serial link, why the router LSA shows two links for that connection. One as 'Connected to another router (point-point)' and another as "Connected to stub network'. Is it same if they are in multi access network ?
Thanks,
Vijaybabu
09-09-2007 11:46 PM
hello,
it's rfc (2328) expected behaviour :
basically, the point2point link is used for topology but doesn't have the IP/mask info that is in the stub network link
Etienne
quoting "http://www.ietf.org/rfc/rfc2328.txt"
For point-to-point interfaces, one or more link
descriptions are added to the router-LSA as follows:
o If the neighboring router is fully adjacent, add a
Type 1 link (point-to-point). The Link ID should be
set to the Router ID of the neighboring router. For
numbered point-to-point networks, the Link Data
should specify the IP interface address. For
unnumbered point-to-point networks, the Link Data
field should specify the interface's MIB-II [Ref8]
ifIndex value. The cost should be set to the output
cost of the point-to-point interface.
o In addition, as long as the state of the interface
is "Point-to-Point" (and regardless of the
neighboring router state), a Type 3 link (stub
network) should be added. There are two forms that
this stub link can take:
Option 1
Assuming that the neighboring router's IP
address is known, set the Link ID of the Type 3
link to the neighbor's IP address, the Link Data
to the mask 0xffffffff (indicating a host
route), and the cost to the interface's
configured output cost.[15]
Option 2
If a subnet has been assigned to the point-to-
point link, set the Link ID of the Type 3 link
to the subnet's IP address, the Link Data to the
subnet's mask, and the cost to the interface's
configured output cost.[16]
09-10-2007 12:22 AM
Hi,
Thanks for the info.
But whats the use of it ?
Thanks,
Vijaybabu
09-10-2007 12:46 AM
hello
that's because of the router lsa format :
for the p2p link type, linkid is set to the neighbor routerid (used for building the net topology). There's not enough room in the link data (32bits) to store IP+mask of the p2p link thus the need for another link (stub)
well, that's how i understand this ;)
regards
etienne
09-10-2007 09:09 PM
Hi all,
Can anyone clear my doubt ?
Thanks,
Vijaybabu
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