OSPF design

[achampag]

Hi,

I have 2 ABR routers in Area0 These routers also talk to area 20. Here is my question. I have multiple site that connect (through Lan 802.1q trunk) to both theses routers (HSRP). Now I have a those 2 ABR routers see each other as OSPF neighbor on every sub-interface (dot1q) in the area 20. Is this the proper way to implement this type of architecture? Is there a way to avoid ospf adjacency on each sub-interface? Will this cause any problems ?

regards

Alex

[Harold Ritter]

You don't need to form an adjacency on all these Vlan interfaces. For redundancy purposes that doesn't buy you much since they are all using the same phisycal trunk. Right?

Use the passive-interface vlanxxx command so that the two routers don't form an adjacency on the interface specified.

[ruwhite]

I wouldn't run OSPF over all of these interfaces, either. I would probably run passive-interface default, and then no passive the few interfaces you actually want to run OSPF on.

Russ.W

[achampag]

diagram in the previous message did not come up as expected. the two ABR`s are connected to each other via two switches.

[achampag]

True,

But if i loose one of the ABR then the site will not converge on other ABR since it does not have an ospf adjacency on on it here is the setup

RA

|

|

switch----------switch

| |

| |

ABR1 ABR2

All the links are dot1q trunks if i loose ABR1, RA can talk to ABR2. But like I mentionned, now ABR1 and ABR2 have a neighbor adjacency on that sub-int. We will have approx 20 sites connecting to those ABR`s

Alex

[ruwhite]

It's okay if you run ospf over a couple of the links between the routers, but not all of them. When you say you have twenty neighbors over these interfaces, what do you mean? You have neighbors on these 20 links, so you have to run ospf on them?

Russ.W

[achampag]

Correct, that is the source of my problem. I want tgeh neighbor adjacency between the remote router and the two ABR's but not another adjacency between the two ABR's within area 20.

[ruwhite]

Then set the link to ospf link-type non-broadcast, and use neighbor statements to build an adjacency only between the routers you want on the link.

http://www.cisco.com/en/US/tech/tk365/tk480/technologies_tech_note09186a008009470d.shtml#config2

Might help....

:-)

Russ.W

[achampag]

Hi Russ,

you're right that is a workaround for this problem but very time consuming for maintenance. Is there a problem with having 20 or more adjacency with the same router-id on different su-interfaces besides the load on the router (sub-optimal routing or area partition etc..)

thanks again for your help

Alex

[ashok_boin]

Hi,

Except unnecessary load, there is no issue. But it's better, to have less adjacencies.

Regards...

Ashok.

[achampag]

Thanks to all for your help

Alex

[ruwhite]

No, there shouldn't be.... Hmmm... I wonder if you could use the type 3 flood blocking to keep from reflooding to each of the peers that are the same router, and just let them form adjacencies? That would block type 3's, but nothing else, but it might provide some increased scaling. Overall, though, those 20 adjacencies aren't going to make any real difference in the network. It would take more on the order of 100's, I would think, to actually be something to worry about.

Russ.W