From: Eugene Ward (eward15@juno.com)
Date: Fri Apr 14 2006 - 13:58:42 GMT-3
Let's summarize:
Here are the original questions posted:
(1) OSPF always prefers intra-area routes over inter-area routes, regardless of the route cost right?
(2) Is there anyway to get a router to prefer an inter-area route?
Answers:
(1) Yes.
(2) Short answer, yes.
Long answer, it depends on the context of the question. If you are referring to changing the behavior of OSPF WITHIN OSPF, then no. If you are using some feature EXTERNAL to the OSPF protocol, then yes, it is possible.
Any thoughts?
Eugene
----------------------------------------------------------------------
Back to the point I made...I think you should look at the requirement
again and see what is intended. PBR accomplishes the requirement and so
does the tunnel. There is no OSPF functionality to make this happen.
Intra over Inter. That's it...cant break IOS!!! Match the route with ACL
and tell it where to go. Now if you had a Riverstone 3000it could do it
all day but we don't have those in the lab.
Faryar
-----Original Message-----
From: Brian McGahan [mailto:bmcgahan@internetworkexpert.com]
Sent: Friday, April 14, 2006 9:02 AM
To: Eugene Ward; Fire_Ice@verizon.net
Cc: Brian Dennis; apilcher@itgcs.com; Faryar Zabihi (fzabihi);
ccie.jimmy@gmail.com; ccielab@groupstudy.com
Subject: RE: OSPF route preferencing
Yes that would just create another intra-area route. You could
filter out the intra-area route with a distribute-list to stop it from
being installed in the routing table. It depends on the specific
topology though.
HTH,
Brian McGahan, CCIE #8593
bmcgahan@internetworkexpert.com
Internetwork Expert, Inc.
http://www.InternetworkExpert.com
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> -----Original Message-----
> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf
Of
> Eugene Ward
> Sent: Friday, April 14, 2006 10:33 AM
> To: Fire_Ice@verizon.net
> Cc: Brian Dennis; apilcher@itgcs.com; Fire_Ice@verizon.net;
> fzabihi@cisco.com; ccie.jimmy@gmail.com; ccielab@groupstudy.com
> Subject: RE: OSPF route preferencing
>
> ZeroFlash,
>
> With your answer, aren't you just creating another intra-area route,
> thereby not really changing the decision process?
>
> Eugene
>
> ----------------------------------------------------------------------
>
> Brian --
>
> PBR does not answer the question as you stated, but creating a tunnel
via
> tunnel interfaces or virtual-links can change the route decision
process
> inside the OSPF process, correct?
>
> Depending on the area that the tunnel interfaces are..
>
> ZeroFlash
>
> -----Original Message-----
> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf
Of
> Brian Dennis
> Sent: Friday, April 14, 2006 10:39 AM
> To: Aaron Pilcher; ZeroFlash; Faryar Zabihi (fzabihi); James Simons;
Cisco
> certification
> Subject: RE: OSPF route preferencing
>
> Of course you can use all kinds of methods to have the "routing
table"
> prefer one route over another but that wasn't the question. The
> question was basically asking if inter-area routes can be preferred to
> intra-area routes. With PBR you are overriding the routing table but
> not changing the route selection process within OSPF itself. The
> problem I have with your answer is that people will now assume that
they
> can get PBR to have OSPF select inter-area routes over intra-area
routes
> which isn't true.
>
> Brian Dennis, CCIE #2210 (R&S/ISP-Dial/Security)
> bdennis@internetworkexpert.com
>
> Internetwork Expert, Inc.
> http://www.InternetworkExpert.com
> Toll Free: 877-224-8987
> Direct: 775-745-6404 (Outside the US and Canada)
>
>
> -----Original Message-----
> From: Aaron Pilcher [mailto:apilcher@itgcs.com]
> Sent: Friday, April 14, 2006 4:54 AM
> To: Brian Dennis; 'ZeroFlash'; 'Faryar Zabihi (fzabihi)'; 'James
> Simons'; 'Cisco certification'
> Subject: RE: OSPF route preferencing
>
>
>
> I 110% agree, but you could force a single ospf router to route over
an
> inter-area route when the ospf process would naturally select an
> intra-area route. I mean, making "unnatural" stuff happen is
what PBR
> is all about.
>
>
>
>
> -----Original Message-----
> From: Brian Dennis [mailto:bdennis@internetworkexpert.com]
> Sent: Thursday, April 13, 2006 11:37 PM
> To: Aaron Pilcher; ZeroFlash; Faryar Zabihi (fzabihi); James Simons;
> Cisco certification
> Subject: RE: OSPF route preferencing
>
> To have inter-area routes preferred over intra-area routes, policy
based
> routing (PBR) will not work. PBR can not alter the route selection
> process within OSPF itself. So this means that if the requirement is
to
> prefer inter-area over intra-area OSPF routes, PBR will not meet the
> requirement.
>
> HTH,
>
> Brian Dennis, CCIE #2210 (R&S/ISP-Dial/Security)
> bdennis@internetworkexpert.com
>
> Internetwork Expert, Inc.
> http://www.InternetworkExpert.com
> Toll Free: 877-224-8987
> Direct: 775-745-6404 (Outside the US and Canada)
>
>
> -----Original Message-----
> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf
Of
> Aaron Pilcher
> Sent: Thursday, April 13, 2006 7:45 PM
> To: 'ZeroFlash'; 'Faryar Zabihi (fzabihi)'; 'James Simons'; 'Cisco
> certification'
> Subject: RE: OSPF route preferencing
>
> To add to your points, PBR would also fit the bill.
>
> -----Original Message-----
> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf
Of
> ZeroFlash
> Sent: Thursday, April 13, 2006 9:27 PM
> To: 'Faryar Zabihi (fzabihi)'; James Simons; Cisco certification
> Subject: RE: OSPF route preferencing
>
> Creating a tunnel would certainly help in learning routes from one
area
> to
> another to influence route selection based on inter/intra area routes.
> The
> only with this is to be careful not to learn your tunnel routes
through
> the
> tunnel or you'll get recursive routing and the tunnels will bounce.
>
> I would also think about another type of tunnel, perhaps a
virtual-link
> here
> might help.
>
> Just some thoughts off the top o the head.
>
> Later...
>
> ZeroFlash
> -----Original Message-----
> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf
Of
> Faryar Zabihi (fzabihi)
> Sent: Thursday, April 13, 2006 10:20 PM
> To: James Simons; Cisco certification
> Subject: RE: OSPF route preferencing
>
> As you might well know...AD will not work here. You might be able to
> accomplish this through having another OSPF process but haven't tried.
> You can also change routing protocol for those routes(but you probably
> don't want that) Also if you want to get yourself into a mess read
> this(I have and never implemented)
>
http://mirrors.isc.org/pub/www.watersprings.org/pub/id/draft-mirtorabi-o
> spf-tunnel-adjacency-00.txt
> I suggest you take a step back and see what the requirement really
wants
> you to do.
>
> Faryar Zabihi
>
> -----Original Message-----
> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf
Of
> James Simons
> Sent: Thursday, April 13, 2006 6:51 PM
> To: Cisco certification
> Subject: OSPF route preferencing
>
> Hello all,
>
> Another OSPF question for you all. OSPF always prefers intra-area
> routes over inter-area routes, regardless of the route cost right? Is
> there anyway to get a router to prefer an inter-area route? If there
> are multiple methods, I would like to know as many of them as possible
> since you never know what you will be allowed to do in the lab.
>
> thanks,
>
> Jimmy
This archive was generated by hypermail 2.1.4 : Mon May 01 2006 - 11:41:57 GMT-3