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Re: OSPF with Multiple ABR & ASBR

  • From: isabel dias
  • Date: Fri Nov 14 11:06:39 2008

Patel,

I would suggest you to read a few things about the path selection algoritm....as if i understand your words you are asking for an issue on LSA type 4 rather than multiple AS and therefore LSA type 5 /7-ASBR

prefer backbone intra-area paths over inter-area paths....

Excerpted from RFC 16.4.1...- When multiple intra-AS paths are available to
ASBRs/forwarding addresses some rules using different costs apply when the same ASBR is reachable through multiple areas, or when trying to decide which of several AS-external-LSAs should be preferred. In the former case the paths all terminate at the same ASBR, while in the latter the paths terminate at separate ASBRs/forwarding addresses. 

http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a0080124c7d.shtml


.//ID



--- On Fri, 11/14/08, devang patel <devangnp@xxxxxxxxx> wrote:

> From: devang patel <devangnp@xxxxxxxxx>
> Subject: Re: OSPF with Multiple ABR & ASBR
> To: "Patrick Darden" <darden@xxxxxxxx>
> Cc: nanog@xxxxxxxxx
> Date: Friday, November 14, 2008, 4:52 PM
> Sorry about that!!!
> 
> 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.
> 
> 
> Answers:
>  I have two T1 line to the non-backbone area and both T1s
> are terminated to
> the two different routers on non-backbone area as well as
> to backbone area,
> and I dont want to achieve primary and secondary role, I
> want to go for the
> load sharing kind of scenario. All sites are connected with
> the central
> site.
> 
> ABR means Area border router only.
> 
> I am attaching one generalized diagram, please look at that
> one.
> Now I want to achieve the load balancing between the
> traffic going from R1
> to R8, I want to achieve some of the networks on R1 should
> be reachable via
> R2 and some of them via R3 for the traffic coming from the
> R8.  assume all
> links are same.
> 
> regards
> Devang Patel
> 
> 
> On Fri, Nov 14, 2008 at 9:29 AM, Patrick Darden
> <darden@xxxxxxxx> wrote:
> 
> >
> > 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
> >>
> >>
> >