North American Network Operators Group
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Re: OSPF with Multiple ABR & ASBR

  • From: Patrick Darden
  • Date: Fri Nov 14 10:29:15 2008

First, without any details, it sounds like you might be better off with static routes than with OSPF. I'm not trying to be patronizing, but you don't mention many details, and some of the details you omit are the crucial ones for OSPF.

1. Do these remote areas have multiple paths to the central area for failover? E.g. a 10Mbps Metro Ethernet primary link, and a 1.5Mbps DSL secondary?
2. Does the central area have multiple routers for failover? E.g. a Cisco 7200 for the incoming Metro Ethernet primary connections, and a Cisco 3660 for the slower secondary connections?
3. Are there any tie-ins between the remote sites that bypass the central site? E.g. site1 and site2 both communicate to the central site via Metro Ethernet, and they also communicate to eachother via DSL.

If none of the above are true, then static routes would be better for you (for the remote area/s in question). E.g. area1 has multiple paths, so ospf is warranted; however, area2 has just one path so a static approach would usually be better.

Your language seems to indicate that OSPF is warranted (area0, area1, two ABRs). I am assuming you mean Area Border Router not Associative Based Routing (vs. OSPF). I am also assuming this is a non-public system (internal network, probably a MAN or WAN).

If so, without any further details, I would set it up for bandwidth/failover. Weight the paths appropriately. Keep it as simple as you can. OSPF can become a morass.

If you sketch your situation out more, we can be more helpful.... Campus? MAN? How public? Multi-pathed? Multi-homed? Multiple interlinks? Are there some lines with reliability problems where the lower bandwidth links are actually preferred? Do you have any decentralized concentration points that might have problems due to multiple remote sites shuttling traffic through it (due to multiple interlinks)?

--p

devang patel wrote:
Hi All,

I am not sure is this the good place to ask this question or not!!!

I am looking for feed back on having OSPF multi-area, lets say if you have
multiple location in nonbackbone areas and those nonbackbone areas are
connected with the one backbone area. For example: OSPF AREA1 has the
connectivity to OSPF AREA0 using two ABR, so what is the optimum way to
achieve the load balancing or load sharing for traffic entering or leaving
the area, what are the possible way to configure it?

regards
Devang Patel