From: Carlos Alberto Trujillo Jimenez (carlos.trujillo.jimenez@gmail.com)
Date: Sat Mar 08 2008 - 12:28:35 ARST
Hi Group.
I solved task 3.7, but a different way from the Solution Guide that seems to
be incorrect the answer in the solution guide.
First, let remember what the task is asking:
- Configure the OSPF domain in such a way that R5 uses R1 to get to VLAN
2,6,7,11 AN 367
- In the case the frame relay circuit between R1 and R5 is down, this
traffic should be rerouted to R2.
- Don not use the ip ospf cost, bandwidth, virtual-link, stub, or nssa
commands to accomplish this.
My solution:
In R2 I modified the cost of the area 0 networks that R2 is advertising to
the area 1 (router 5 is memeber of area 1). As the restriction states to not
use the command "IP OSPF COST", I modifyed the cost, but NOT USING THE
COMMMAND "IP OSPF COST", so for me it seems my answer is ok, Im not
violating any restriction.
Router 2:
router ospf 1
area 1 range 139.1.2.0 255.255.255.0 cost 10000
area 1 range 139.1.11.0 255.255.255.0 cost 10000
area 1 range 139.1.0.0 255.255.255.0 cost 10000
area 1 range 139.1.6.0 255.255.255.0 cost 10000
As a result I cheekd R5 routing table and it has entries to vlans 2,6,7,11
and 367 pointing to its prefered next hop R1 (router 1 is advertising the
same networks as router 2, but with a better cost).
I tested shutting down R1 link to the frame-relay network, and the routes
are reachable now by its next hop R2.
2008/3/8, Herbert Maosa <asawilunda@googlemail.com>:
>
> Hi Guys,
>
> I have tried to lab this again and again and my result seem to disagree
> with
> the solution to task 3.7 of IEWB lab 13. So either I may be missing
> something very fundamental as the output from the solutions guide shows
> that
> it should work. So hopefully one of you can shed more light on my gaps
> here.
>
> R1,R2,R6,SW1 ,R3a re originating VLANS 11, 2,6,7 and 367 respectively into
> OSPF . R5 has adjacencies with R1 and R2 and recieving these prefixes. The
> question is configure R5 such that it prefers the path towards R1 and only
> use R2 as a backup.
>
> The solution is to lower the OSPF distance for these routes when they are
> learned from R2.
>
> *distance 109 150.1.1.1 0.0.0.0 VIA_R1
>
> *VIA_R1 is a standard access-list that matches the desired routes.
> 150.1.1.1is the ospf router-id of R1. Now, when I configure this way,
> only VLAN 11 (
> 139.1.0.0/24) has the distance lowered to 109 and R5 prefers this path
> when
> R1 is available. This is what I expect to happen and it is what I am
> seeing
> in the lab, as my understanding is that in the distance command above ,
> 150.1.1.1 has to be the advertising router-id, and not the next hop from
> which you learnt the LSA. So because R1 is only originating VLAN 11, it
> seems to work that way, but the other routes are not affected even though
> they are learnt from R1 because they are originated form somewhere else.
>
> Now, the show command output from the solutions guide seems to show all
> these prefixes with their distance changed to 109, which is suggesting
> that
> the 150.1.1.1 in the distance command would be the router-id of the
> next-hop
> router that you learnt the prefixes from, and not necessarily the
> advertising router.
>
> Can someone open my eyes here ? I have tried to find my own asnwer by
> labbing this over and over again and I can not reproduce the solution
> provided, even if I copy and paste the config from the solutions guide
> as-is.
>
> Herbert.
>
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