Re: OSPF with Multiple ABR & ASBR

From: isabel dias (no email)
Date: Fri Nov 14 2008 - 11:06:30 EST

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    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 <> wrote:

    > From: devang patel <>
    > Subject: Re: OSPF with Multiple ABR & ASBR
    > To: "Patrick Darden" <>
    > Cc:
    > 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
    > <> 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
    > >>
    > >>
    > >

          


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