Routing neighborships over a secondary IP

Unanswered Question
Aug 30th, 2007
User Badges:

Hi everyone-

I was wondering if there was a way to force an OSPF or EIGRP neighborship to take place over a secondary IP address, as well as a primary IP address?

It's my understanding that OSPF / EIGRP do not normally do this, and I was hoping there was a way to configure them to do so without having two interfaces.

Thanks for your help!

  • 1
  • 2
  • 3
  • 4
  • 5
Overall Rating: 3.8 (3 ratings)
JORGE RODRIGUEZ Thu, 08/30/2007 - 16:27
User Badges:
  • Green, 3000 points or more

Hi Cory, your understanding is correct.. both routing protocols have completely different mechanism from one another as well as metrics. The only way they can co-exist is by redistribution.

Richard Burts Thu, 08/30/2007 - 18:17
User Badges:
  • Super Silver, 17500 points or more
  • Hall of Fame,

    Founding Member

  • Cisco Designated VIP,

    2017 LAN, WAN


My understanding of your question is a bit different than Jorge's. I believe that you are asking about having the routing protocol establish a neighbor relationship using the secondary address. Neither protocol is able to establish neighbor relationship using the secondary address. They only form neighbor relationship using the primary address. They will happily advertise the secondary address. But they will not establish a neighbor relationship using the secondary address.

Is there some reason why you want them to establish neighbor relationship using the seconday address?



JORGE RODRIGUEZ Thu, 08/30/2007 - 19:10
User Badges:
  • Green, 3000 points or more

Hi Rick, interesting, the way I had understood Cory's question was whether if

having an ospf interface primary or seconday IP address be able to also peered or stablish eigrp adjecency on that same interface or the other way around.



mohammedmahmoud Thu, 08/30/2007 - 23:33
User Badges:
  • Green, 3000 points or more


I think Rick's interpretation of the question is perfect, and to say it in another prospective, OSPF sees secondary networks as stub networks (networks on which there are no OSPF neighbors) and therefore will not send Hellos on them. Consequently, no adjacencies can be established on secondary networks.

And more over, OSPF will advertise a secondary network or subnet only if it is also running on the primary network or subnet (there must exist 2 network commands, one for the primary and the other for the secondary).


Mohammed Mahmoud.

cskjervem Fri, 08/31/2007 - 05:25
User Badges:

Thanks for the responses guys, it is unfortunate that it cannot be done, but I appreciate it. Maybe there is another way of doing what I wanted.

What I am trying to do:

I have a IP radio network (256k bandwidth, long range), that acts like an ethernet LAN. I want to add increased speed to the endpoints on this radio network, so I was going to add DSL to each of our 10 sites, and then configure DMVPN to look back to our main site over the DSL. I was then going to use OSPF or EIGRP for routing. Unfortunately, without multiple subnets, I cannot think of a way to force the traffic to go over the DSL link and not the radio ethernet link.

Just for illustration purposes, the subnet running on the radio ethernet is a subnet. This is the subnet which our end computers are configured on at each remote site. If I add DSL links and configure DMVPN on them, the traffic will still go over the ethernet radio instead of the DSL. Since I was looking at routers with a single LAN interface (to keep costs down), I cannot think of a way to add multiple subnets to the LAN int without VLAN capabilities, something that ethernet radio does not support (or the switches located at each site).

Does anyone know of a way to force traffic over the DSL link instead of the ethernet radio (which again, acts like a LAN)?

If not, is there a way to add multiple subnets to a single LAN int without a secondary IP or VLAN configuration?

Thanks for all of your help!


This Discussion