Cisco Support Community
cancel
Showing results for 
Search instead for 
Did you mean: 
Community Member

OSPF NBMA ?

Hi,

Doyle Volume I p.416/417 'Network Types' states "OSPF routers on NBMA networks elect a DR & BDR, and all OSPF packets are unicast."

Is the above statement correct ?

My understanding of the DR/BDR election process is that multicast would be used to 224.0.0.5 (AllOSPF) and 224.0.0.6 (AllDRouters).

Phil.

2 REPLIES
Silver

Re: OSPF NBMA ?

What Jeff is refering to is the fact that in order to make OSPF operate on NMBA media (like FR) you need extra configuration to discover neighbors; the use of the 'neighbor' command. When you configure this command the OSPF messages are unicast to the neighbor.

Your understanding is correct for broadcast multiaccess media like ethernet.

That being said there are other ways to configure OSPF on NBMA that basically avoid having to elect a DR and use the neighbor commands. Such mechanism usually require changing the ospf network type to either point-to-point or point-to-multipoint. If you need detailed information on OSPF the following is a great place to start:

http://www.cisco.com/en/US/tech/tk365/technologies_white_paper09186a0080094e9e.shtml#t25

Re: OSPF NBMA ?

phil,

you can have more clear idea of DR election in NBMA by reading the jeff doyle vol1 CASE STUDY OSPF OVER NBMA NETWORK...

when you configure neighbour with command neighbour then tehy will transfer the hello in unicast mode...at that time all router will make their static list of router with their interface ip address and the priority and on the base of priority they will elect the DR ...normally in hub and spoke topology you can have to configur you HUB router as a DR so you have to make it priority hight than other because of all router in hub and spoke topology having connectivity with hub router ...

YOU WILL HAVE MORE CLEAR PICTURE AFTER READING THAT CASE STUDY

hope this will clear your idea

rate this post if it helps

regards

Devang

290
Views
8
Helpful
2
Replies
CreatePlease to create content