IIRC, OSPF works on the basis of path cost. To make the router Prefer a
path, you
A. Raise the cost of the bad link above the good link
or
B. Lower the cost of the good link below the bad link
>From CCO, I see that
---Begin quote from
http://www.cisco.com/cpress/cc/td/cpress/design/ospf/on0407.htm
The cost associated is determined (default) by the interface bandwidth
statement unless otherwise configured to maximize multiple path routing.
Before Cisco's IOS release 10.3, the default cost was calculated by dividing
1,000,000,000 by the default bandwidth of the interface. However, with IOS
releases after 10.3, the cost is calculated by dividing 1,000,000,000 by the
configured bandwidth
---End quote from
http://www.cisco.com/cpress/cc/td/cpress/design/ospf/on0407.htm
There are two paths from A to C.
a-c
a-b-d-c
Since you want to prefer the a-b-d-c link in the least amount of
configuration possible, then you would increase the cost of the a-c link.
This can be done based on the configured bandwidth of the link, or using the
ospf Cost command. Example...
config term
interface serial 0/0
description RouterAs connection from RouterA to RouterC
Router(config-if)#ip ospf cost ?
Cost
Router(config-if)#ip ospf cost 65534
Since this link has an excessively high cost, ospf should use the other
link. You will also have to do this on Router C so that the traffic will
take c-d-b-a as the preferred route back.
BTW, if you ping RouterC's serial link, it will still go from a-c because
it's a connected interface. If you trace a host served by routerC it should
go a-b-d-c.
Let me know If I'm incorrect,
Ejay Hire
-----Original Message-----
From: Kevin Schwantz [mailto:[EMAIL PROTECTED]]
Sent: Tuesday, May 29, 2001 10:03 AM
To: [EMAIL PROTECTED]
Subject: Re: Wanna Be a CCIE? Try This One [7:6076]
routerA routerB
AREA0--------AREA0
| |
routerC routerD
AREA1---------AREA1
Since we are on the topic of OSPF, could someone help me out on the scenario
above?
Routers A and B have interfaces in Area 0 and Area1. I want traffic from
routerA destined for routerD to go via router B. This is not the case in my
network because I realise that routerA prefers Intra-Area routes and thus
would route traffic to routerD via routerC.
What tweaks must I make in order to force the traffic from routerA to
routerD to go via routerB ? Someone suggested building a GRE tunnel between
routerA and routerB and then configure the tunnel to be in AREA1.
Any suggestions?
Kevin
""W. Alan Robertson"" wrote in message
[EMAIL PROTECTED]">news:[EMAIL PROTECTED]...
> Guys,
>
> The actual traffic will not be routed up to area 0... Area 0 has been
> extended
> down to R2, so R2 is now a backbone router. R2 has interfaces in 3 areas
> now:
> Area1, Area2, and Area0 by means of it's virtual link.
>
> Any traffic originating in Area2 destined for Area1 will be routed
directly
> by
> R2. This satisfies the "Interarea traffic must traverse the backbone"
rule,
> because R2 *is* a backbone router.
>
> This is not theory... It is fact.
>
> Alan
>
> ----- Original Message -----
> From: "Andrew Larkins"
> To:
> Sent: Monday, May 28, 2001 10:13 AM
> Subject: RE: Wanna Be a CCIE? Try This One [7:6076]
>
>
> > agreed....to area 0 then on to the intended area
> >
> > -----Original Message-----
> > From: Circusnuts [mailto:[EMAIL PROTECTED]]
> > Sent: 28 May 2001 15:50
> > To: [EMAIL PROTECTED]
> > Subject: Re: Wanna Be a CCIE? Try This One [7:6076]
> >
> >
> > Chuck- my answer is Yes. The traffic from the Virtual Linked psuedo-ABR
> > passes back to Area 0, before it's sent onto the intended Area (even if
> it's
> > directly connected).
> >
> > Phil
> >
> >
> > ----- Original Message -----
> > From: Chuck Larrieu
> > To:
> > Sent: Sunday, May 27, 2001 8:59 PM
> > Subject: Wanna Be a CCIE? Try This One [7:6076]
> >
> >
> > > Ever wonder what the CCIE candidates talk about on the CCIE list?
> > >
> > > The following message came through today. I thought the bright folks
on
> > this
> > > list might be curious, and might want to venture an answer.
> > >
> > > Begin original question:
> > >
> > > Guys,
> > >
> > > I wonder if there is anybody who remembers the discussion on Virtual
> > > Links in OSPF. It was posted some time ago but I can't seem to find
it.
> > >
> > > The scenario was something like this:
> > > ________ _______ _______
> > > |Area 0 | |Area1| |Area2|
> > > | R0 |--| R1 |--| R2 |
> > > |______| |_____| |_____|
> > >
> > > There is a virtual link from area 2 to Area 0 via Area1. Traffic needs
to
> > > get to R1 in Area 1 from R2 in Area 2. Assume that the virtual link
has
> to
> > > use R1 (To create the V.Link). Does the traffic flow passed R1 (in
Area
> 1)
> > > to Area 0 and then back to area 1, or does the actual flow just to R1
> from
> > > R2.
> > >
> > > I cant remember the conclusion, and I cant seem to find it on the
> > archives.
> > > Quite interesting issues.
> > >
> > > End of original question
> > >
> > >
> > > Chuck
> > >
> > > One IOS to forward them all.
> > > One IOS to find them.
> > > One IOS to summarize them all
> > > And in the routing table bind them.
> > >
> > > -JRR Chambers-
> > > FAQ, list archives, and subscription info:
> > http://www.groupstudy.com/list/cisco.html
> > > Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
> > FAQ, list archives, and subscription info:
> > http://www.groupstudy.com/list/cisco.html
> > Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
> > FAQ, list archives, and subscription info:
> http://www.groupstudy.com/list/cisco.html
> > Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
> FAQ, list archives, and subscription info:
http://www.groupstudy.com/list/cisco.html
> Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
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