OSPF with Multiple ABR & ASBR

Patrick Darden darden at armc.org
Fri Nov 14 09:29:07 CST 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
>   




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