OSPF Network Type

[BaconandEggs]

Hello all,

First question in the community, excited to be here. A customer system and my system will be connecting over OSPF. Here's the architecture:

We have a private WAN, L3 connection between both systems. I have 2 routers connecting to them in total, both are in separate locations.

The first router was given an IP of 10.60.13.37 and the second router was given an IP of 10.60.13.45. They are in different subnets as they are in /29s. The default gateway for each lives on the customer system. I don't know if the customer has a single router or 2 routers on their end.

In this scenario, I don't really need a DR/BDR elected, so I'm thinking point-to-point. However, I'm not sure if there is a single router or 2 routers on their end, as we connect to their MPLS system and I have no idea where it goes. If they have more than 1 router, should I choose point-to-multipoint?

My question is what OSPF network type should I implement?

Thanks.

[balaji.bandi]

If they connecting to your same Router and other side More than 1 Router (i would go with Point to Multi Point#)   - If you do not want  DR/BDR  then go with point-to-point. on high level p2p not scaled as expected.. ( again this is based on information).

[BaconandEggs]

Balaji,

Thanks for the response. I have 2 routers in geographically separate areas. I do need to find out if they terminate at the same router or 2 separate routers on the customer end.

In scenario #1, I will have 2 routers on my end (with the IP information previously listed) and they both connect to a single router on the customer end. (3 router in total)

In scenario #2, I will have 2 routers on my end (with the IP information previously listed) and they each connect to a corresponding router on the customer end. (4 routers in total)

Yes, I don't need to scale in this situation. Could I do point-to-point in both these scenarios? I have been trying to find if I could use the same process ID and area between all the routers (whether its 3 or 4 depending on the scenario), but haven't found that answer.

Will using the same process id and area # cause issues in a point to point? Everything online only shows topologies for 2 routers, but in my case, it will be either 3 or 4.

Thanks,

B&E

[Naseer Anjan]

@BaconandEggs 

Well, Process ID is Global identifier local to this router means locally significant. so you can use same OSPF process ID which recommended too. Secondly, area ID can be same or different for these two links but recommended one is to be same  area ID. So, you can reduce complexity and burden of your router & routing. Finally, Point to Point or Broadcast which will be only between two routers and only those specific link as you will have different subnet for each link. Hence, you can make it Point to Point that will skip DR/BDR election process and Type2 LSA. 

[paul driver]

Hello

you need follow the network type that the providers are using you cannot simply just choose a different type otherwise the adjacency won’t establish. 

[BaconandEggs]

Paul,

Thanks for your input. While the customer provided the IP info, I have the responsibility to determine the network type.

Thanks,

B&E

[Giuseppe Larosa]

Hello @BaconandEggs ,

if the routers at the two sites are in different sites they cannot become OSPF neighbors

>> The first router was given an IP of 10.60.13.37 and the second router was given an IP of 10.60.13.45. They are in different subnets as they are in /29s. The default gateway for each lives on the customer system. I don't know if the customer has a single router or 2 routers on their end.

You need to know how many routers are in remote site and what protocol you can use with the MPLS network:

if it is an MPLS L3 VPN service the peer of your router will be the local PE node and not the remote site router(s)

if MPLS L3 VPN what PE-CE protocol is in use / can you use ? static routes, eBGP or OSPF ?

So you need to understand what kind of MPLS service is in place between the two sites.

The OSPF network type is really the last question you should ask, you need to clarify the above first.

Hope to help

Giuseppe

[BaconandEggs]

Giuseppe,

Thanks for your input. Currently, we don't have OSPF set up between us, but they run OSPF in their MPLS network. I'm fairly confident that they use a VPLS service between us, and the connection between us is currently static and layer 2 and moving to OSPF/layer 3.

Thanks,

B&E

[Richard Burts]

B&E

I have several comments:

- First I wonder why you are so concerned about DR/BDR or not. Manipulating the network type just makes the configuration more complex. And more complex invites issues about how the configuration should work. Until we know more about the environment my suggestion is to just configure OSPF on the interfaces and let OSPF use its default behavior for that type of interface.

- Also we do not know much about this environment and about how these routers are connected. As we find out more it may become clear that some of the fancy/more complicated configurations are appropriate. But for now I advocate for keeping things simple, and using default behaviors when possible.

- 2 routers connected to each other and running OSPF absolutely MUST use the same area ID. If routers running OSPF do not agree on the area ID then they will not form a neighbor relationship.

- the process ID is locally significant. So it does not matter to a router which process ID the neighbor is using. So you could use the same process ID in each (and I might like that as part of keeping things simple). Or you could use a unique process ID in each and it will not matter.

[MHM Cisco World]

follow

[Naseer Anjan]

Point to Point is the right option whether they use same or different routers. also, you have mentioned that Private WAN, is it Ethernet ? and connecting to your router's Ethernet interface ? if so, by default it will be Broadcast and you need to check with your other end and get the mutual agreement of interface network type in this case.