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Tuning OSPF on Ethernet /30 Links?

Hello,

there are often many /30 ethernet point-to-point links in the core and distribution part of a campus network and OSPF is the routing protocol running over those links.

Has anyone ever tried to configure these links as OSPF network type point-to-point? I did some tests and I think this could save some convergence time because no DR/BDR must be elected. Further the Link State Database is much shorter because there are no LSAs Type 2.

Thanks for your reply

1 ACCEPTED SOLUTION

Accepted Solutions
Gold

Re: Tuning OSPF on Ethernet /30 Links?

I've tested this in the lab, and it works. Further, you should be able to use /31's on those point-to-point links, and save a little more address space.

Russ.W

5 REPLIES
Silver

Re: Tuning OSPF on Ethernet /30 Links?

yes I have done this , howecer the database is larger because a network entry is made for each point to point link, this is not really an issue though

Gold

Re: Tuning OSPF on Ethernet /30 Links?

Actually, the database will be smaller, not larger.... :-) What you normally get with a broadcast link is this:

rtr1----(p-node)----rtr2

Normally, rtr1 and rtr2 would advertise a 0 cost connection to the p-node, the type 2 LSA, and the DR would advertise a type 2, with connections to rtr1 and rtr2, with the real link cost. This means you have an extra type 2in your database, and an extra node in your spf tree.

Making this link a point-to-point actually drops the type 2, dropping one entire LSA out of your database, and dropping the extra node out of the tree. :-)

Russ.W

Silver

Re: Tuning OSPF on Ethernet /30 Links?

It will drop the type 2 but it will create a type 3 for each /30 configured , hence a larger database

Gold

Re: Tuning OSPF on Ethernet /30 Links?

It should only create a type 3 if it's an ABR, and then it would create a type 3 summarizing all of the network reachable within the area to another area (not just this /30). What it will do is add another link to the type 1, which you are getting anyway, since the link to the type 2 is also a link in the type 1.

:-)

Russ.W

Gold

Re: Tuning OSPF on Ethernet /30 Links?

I've tested this in the lab, and it works. Further, you should be able to use /31's on those point-to-point links, and save a little more address space.

Russ.W

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