From: Swaroop Potdar (swarooppotdar@hotmail.com)
Date: Tue Aug 23 2005 - 14:52:38 GMT-3
Just to increase the fun and challenge may be this could be tried out too.
This would reveal all the things we need to think like a router does.
Bridge two OSPF broken area 0 on a RIP V2 Domain.
1) Case 1
ie: RIP is running btwn R1, R2 and R3.
R1 and R3 are also hosting OSPF area 0.
We need to try and bridge area 0.
(OSPF Area 0) Router1------------router2-------router3 ( OSPF Area 0)
|<----------GRE Tunnel------------->|
2) Case 2:
Now run RIP btwn R2 and R3
OSPF area 1 between R1 and r2.
Plus R1 and R3 hosting broken OSPF area 0's as before.
(OSPF Area 0) Router1------------router2-------router3 ( OSPF Area 0)
(Area 1) (RIP)
|<----------GRE Tunnel------------->|
se0/0---se0/0 fa1/0--fa1/0
(OSPF Area 0) Router1------------router2-------router3 ( OSPF Area 0)
|<----------GRE Tunnel------------->|
>From: "Scott Morris" <swm@emanon.com>
>Reply-To: <swm@emanon.com>
>To: "'Swaroop Potdar'"
><swarooppotdar@hotmail.com>,<aarumuga@hotmail.com>,<tmitchell@allianttech.com>,<thomwin_chen@yahoo.com>,<ChoonHo.Loi@getronics.com>,<ccielab@groupstudy.com>
>Subject: RE: OSPF Virtual-Link & GRE
>Date: Tue, 23 Aug 2005 13:26:53 -0400
>
>It would likely be better to watch your areas more appropriately and try to
>look at exactly what OSPF is thinking when it makes the decision it does.
>That'll help everyone get a much better grasp of the way the OSPF "thought
>process" works!
>
>It seems like you all have the basic cause down, which is good. Now we
>just
>need to look at "why"!
>
>Scott
>
>PS. Look at the decision process of how OSPF selects a route. Then look
>at
>what is being done to the routers. Think like the router does!
>
>-----Original Message-----
>From: Swaroop Potdar [mailto:swarooppotdar@hotmail.com]
>Sent: Tuesday, August 23, 2005 1:24 PM
>To: swm@emanon.com; aarumuga@hotmail.com; tmitchell@allianttech.com;
>thomwin_chen@yahoo.com; ChoonHo.Loi@getronics.com; ccielab@groupstudy.com
>Subject: RE: OSPF Virtual-Link & GRE
>
>guys as Scott rightfully said if you do run across this problem then you
>may
>not use static routes ..
>
>may be u can try filtering the the tunnel destination routes being received
>through the tunnel by a distribute list into the tunnel end point routers.
>
>Or may be you can set the cost of tunnel above par of your maximum cost of
>any prefix in your OSPF domain to be safe.
>
>
>
> >From: "Scott Morris" <swm@emanon.com>
> >Reply-To: "Scott Morris" <swm@emanon.com>
> >To: "'Arun Arumuganainar'" <aarumuga@hotmail.com>, "'Mitchell, TJ'"
> ><tmitchell@allianttech.com>, "'Thomwin Chen'"
><thomwin_chen@yahoo.com>,
>
> > "'Loi, Choon Ho'" <ChoonHo.Loi@getronics.com>,
><ccielab@groupstudy.com>
> >Subject: RE: OSPF Virtual-Link & GRE
> >Date: Tue, 23 Aug 2005 13:01:56 -0400
> >
> >And here I thought static routes weren't allowed on the exam!
> >
> >The reason static routes fix it is because the AD is lower than OSPF is!
> >:)
> >So you'll likely want to figure out another reason/thought on how to fix
> >that in case you run into something like this on the lab!
> >
> >Scott
> >
> >-----Original Message-----
> >From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
> >Arun
> >Arumuganainar
> >Sent: Tuesday, August 23, 2005 9:37 AM
> >To: Mitchell, TJ; Thomwin Chen; Loi, Choon Ho; ccielab@groupstudy.com
> >Subject: Re: OSPF Virtual-Link & GRE
> >
> >Yes ... You are right on top !!!
> >
> >Static route to tunnel destination is a sure solution for this problem
>!!!
> >I
> >have seen similar problem before !!! Just wanted to share with you as it
>is
> >relevant to our discussion .
> >
> > se0/0---se0/0 fa1/0--fa1/0
> >Router1------------router2-------router3
> > |<----------GRE Tunnel------------->|
> >
> >In the above topology ... Do the Basic configuration as follows . This is
>a
> >simple single area topology !!!
> >
> >1) Configure OSPF on R1 , R2 and R3
> >2) Bring up GRE Tunnel between R1 and R3
> >3) Turn on OSPF on GRE tunnel as well .
> >
> >Now the Fun Starts .... Do this peace of configuration over the base
> >topology.
> >
> >ON R1 go to se0/0 increase the OSPF cost to very high value say for ex :
> >1000
> >
> >Now you would see interface flapping .
> >
> >Scenario Note :
> >~~~~~~~~~~
> >
> >Playing with OSPF cost is simple way to channelise all traffic via GRE
> >Tunnel . However in doing so if we are not very care ful even tunnel
> >destination will go via GRE and this would result in Flaps .
> >
> >So Best Practice Recommendation : We are free to tweak the cost but
>ensure
> >that tunnel destination does not take the tunnel route . We can just rely
> >on
> >static route for tunnel destination in the respective tunnel end-points
>!!!
> >
> >Thanks and Regards
> >Arun
> >
> >----- Original Message -----
> >From: "Mitchell, TJ" <tmitchell@allianttech.com>
> >To: "Arun Arumuganainar" <aarumuga@hotmail.com>; "Thomwin Chen"
> ><thomwin_chen@yahoo.com>; "Loi, Choon Ho" <ChoonHo.Loi@getronics.com>;
> ><ccielab@groupstudy.com>
> >Sent: Tuesday, August 23, 2005 6:29 PM
> >Subject: RE: OSPF Virtual-Link & GRE
> >
> >
> >I know I'm new here, but I have an idea on what is going on.
> >
> >On router R3 you are originally learning the route 172.16.25.x through
>the
> >virtual-link of area 1 which is fine it works. Now you are putting the
> >tunnel on through the virtual-link back to the backbone area 0.
> >
> >The tunnel comes up and things are working great.
> >
> >Now guess what happens you start learning the 172.16.25.x route through
>the
> >tunnel instead of the virtual link due to the nature of OSPF. Well when
> >making tunnels with OSPF you need to make sure you don't start learning
> >your
> >destination networks through the tunnel otherwise the tunnel will drop
> >because it will lose the route because the virtual link is now gone. Then
> >the tunnel drops OSPF reconverges and you learn the link again through
>the
> >virtual-link, tunnels comes back up because it has the route to the
> >destination network, OSPF reconverges again you lose the route and the
> >tunnel drops again.
> >
> >You see what I'm saying. Get the tunnel up and running then quickly check
> >the routing tables while you can still ping. You should see that the
>route
> >is learned from the tunnel and not the interface.
> >
> >Like I said I'm new here and this is my thought on the deal, I would like
> >to
> >know your thoughts.
> >
> >Thanks
> >
> >T.J. Mitchell
> >-----Original Message-----
> >From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
> >Arun
> >Arumuganainar
> >Sent: Tuesday, August 23, 2005 8:47 AM
> >To: Thomwin Chen; Loi, Choon Ho; ccielab@groupstudy.com
> >Subject: Re: OSPF Virtual-Link & GRE
> >
> >Cool ... Pretty interesting problem though ... But I would need some more
> >information to confirm my suspicion .
> >
> >Pls. provide me with show ip route <tunnel destination > ... taken at
>two
> >different times .
> >
> >a)When ping packets are going through fine
> >b) when ping are not going through .
> >
> >If my suspicion is right then your tunnel protocol state in the "show
> >interface tunnel 0" command should toggle between UP and DOWN state !!!
> >at
> >regular intervals.
> >
> >Only work around for this problem add a following static route in tunnel
> >end
> >points .
> >
> >R2 .
> >
> >ip route 172.16.35.0 255.255.255.252 serial 1/1
> >
> >R3
> >
> >ip route 172.16.25.0 255.255.255.252 serial 1/1
> >
> >This kind of problems are bound to happen especially when you enable
> >routing
> >protocols on a tunnel interface . Some times routers could have learned a
> >better route for tunnel destination via tunnel interface themselves .
> >This
> >creates a loop . i.e Tunnel recurses over Tunnel destination and tunnel
> >destination reclurse over tunnel !!! Under this scenario there will be
> >flapping of tunnel interface at regular intervals !!!
> >
> >Best way to address it , is to have static route for tunnel destination
> >alone via an interface other than Tunnel .
> >
> >Pls. Note : Static route is always preferred . Hence accidental loops
>will
> >not be introduced through Dynamic Routing protocols .
> >
> >Pls. do let me know if this solves the problem .
> >
> >Thanks and Regards
> >Arun
> >----- Original Message -----
> >From: "Thomwin Chen" <thomwin_chen@yahoo.com>
> >To: "Loi, Choon Ho" <ChoonHo.Loi@getronics.com>; <ccielab@groupstudy.com>
> >Sent: Tuesday, August 23, 2005 3:30 PM
> >Subject: Re: OSPF Virtual-Link & GRE
> >
> >
> > > Choon,
> > >
> > > Have you try to put the tunnel0 interface in R2 and R3 into area 0 ?
> > > I saw your config, the tunnel is in area 3.
> > >
> > > Rgds,
> > > Thomwin
> > >
> > >
> > > "Loi, Choon Ho" <ChoonHo.Loi@getronics.com> wrote:
> > > Hi,
> > >
> > > I lab-up the following Scenario for OSPF:
> > >
> > > Area 0 | R2 -----Area 1------- R5 ------Area 2--------R3--------| Area
> >3
> > >
> > > Everything works fine... but, my ping drop intermittently when I try
> >to
> > > ping from Area3 to Area0.
> > > Anything wrong with my configuration?
> > >
> > > Thanks.
> > >
> > >
> > > Following is my configuration:
> > >
> > > hostname r2
> > > !
> > >
> > > !
> > > interface Loopback0
> > > ip address 192.2.2.2 255.255.255.0
> > > !
> > > interface Tunnel0
> > > ip address 23.23.23.2 255.255.255.248
> > > tunnel source Serial1/1
> > > tunnel destination 172.16.35.1
> > > !
> > > interface Serial1/1
> > > ip address 172.16.25.1 255.255.255.252 encapsulation ppp
> > >
> > > router ospf 1
> > > router-id 2.0.0.2
> > > log-adjacency-changes
> > > area 1 virtual-link 5.0.0.5
> > > network 23.23.23.0 0.0.0.7 area 3
> > > network 172.16.25.0 0.0.0.3 area 1
> > > network 192.2.2.0 0.0.0.255 area 0
> > >
> >------------------------------------------------------------------------
> > > ---
> > > !
> > > hostname r5
> > >
> > > interface Loopback0
> > > ip address 100.100.100.100 255.255.255.0 !
> > > interface Loopback1
> > > ip address 5.0.0.5 255.255.255.255
> > >
> > > interface Serial0/0
> > > ip address 172.16.25.2 255.255.255.252 encapsulation ppp no fair-queue
> > > !
> > > interface Serial0/1
> > > ip address 172.16.35.2 255.255.255.252 encapsulation ppp !
> > > router ospf 1
> > > router-id 5.0.0.5
> > > log-adjacency-changes
> > > area 1 virtual-link 2.0.0.2
> > > network 172.16.25.0 0.0.0.3 area 1
> > > network 172.16.35.0 0.0.0.3 area 2
> > > neighbor 5.5.5.2
> > > !
> > >
> > >
> > >
> >------------------------------------------------------------------------
> > > ------
> > > !
> > > hostname r3
> > >
> > > interface Loopback0
> > > ip address 10.10.10.3 255.255.255.255
> > > !
> > > interface Tunnel0
> > > ip address 23.23.23.3 255.255.255.248
> > > tunnel source Serial1/1
> > > tunnel destination 172.16.25.1
> > >
> > > interface Serial1/1
> > > ip address 172.16.35.1 255.255.255.252 encapsulation ppp serial
> > > restart_delay 0 clockrate 64000
> > >
> > > router ospf 1
> > > router-id 3.0.0.3
> > > log-adjacency-changes
> > > network 10.10.10.0 0.0.0.255 area 3
> > > network 23.23.23.0 0.0.0.7 area 3
> > > network 172.16.35.0 0.0.0.3 area 2
> > >
> >------------------------------------------------------------------------
> > > -------------------------------------
> > >
> > >
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>
>Regards,
>Swaroop.
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Regards,
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