From: Joseph Saad (joseph.samir.saad@gmail.com)
Date: Mon Nov 05 2007 - 14:15:02 ART
Dreadful topic virtual-links really is specially when coupled with
authentication.
To simplify matters, Virtual-link make the router, that is not seemingly
connected to Area 0, have an interface in Area 0. i.e. it becomes an ABR.
i.e. it will contain the 0-area type-1 and type-2 LSA's.
Have a look at show ip ospf database after you establish the virtual link.
Same concept is useful when considering area 0 authentication.
HTH,
Joseph.
On 11/5/07, Scott Vermillion <scott_ccie_list@it-ag.com> wrote:
>
> Joe,
>
> It's possible I'm missing a nuance or two here. But it seems normal to
> me.
> The virtual links are nothing but tunnels for OSPF (not payload according
> to
> my recent research) traffic. Thus, logically, the Virtual links simply
> "move" SW1 and SW2 to the backbone. In that regard, they are everyday
> ABRs
> for Area 211. They will be getting the same backbone LSAs as routers
> physically attached to the backbone and will be implementing the same ABR
> logic and behavior. They do not somehow become subordinate to their
> virtual
> link endpoints that are actually attached to the backbone (i.e. they will
> not be receiving the LSAs that summarize routes into Areas 331 or 422, as
> those LSAs belong to and are originated into areas separate from 211).
>
> "Have I ever mentioned how much I hate Virtual Links?"
>
> Regards,
>
> Scott
>
>
> -----Original Message-----
> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
> Joseph Brunner
> Sent: Monday, November 05, 2007 9:10 AM
> To: 'groupstudy'
> Subject: area 0 range & virtual links
>
> I would like to bring to your attention an interesting issue I ran into
> this
> morning. When summarizing area 0 routes (in this case /32's from a p2mp
> area
> 0 frame relay cloud) virtual links broke the summary, and continued to
> allow
> the /32 lsa's out, instead of just the /24 summary.
>
>
>
> Here is an area 0 router's ospf config
>
>
>
> rack1r2#sh run | b router ospf
>
> router ospf 1
>
> router-id 1.1.2.2
>
> log-adjacency-changes
>
> area 0 authentication message-digest
>
> area 0 range 1.1.20.0 255.255.255.0
>
> area 422 virtual-link 1.1.8.8 authentication message-digest
>
> area 422 virtual-link 1.1.8.8 message-digest-key 1 md5 cisco
>
> network 1.1.2.2 0.0.0.0 area 0
>
> network 1.1.20.2 0.0.0.0 area 0
>
> network 1.1.22.2 0.0.0.0 area 422
>
>
>
> My areas are 0, 422, 331 with 211 being isolated from the backbone. Sw1
> and
> sw2 are in ABR's between 331/211 and 422/211 respectively and the virtual
> link destinations from the "area 0" backbone routers". Between the two
> switches is R1, an internal area 211 router.
>
>
>
> It took putting the "area 0 range 1.1.20.0 255.255.255.0" on sw1 and sw2
> (the ends of the virtual links) to get Router 1 to ONLY see the /24
> summary
> route.
>
>
>
> (before)
>
>
>
> rack1r1#sh ip route 1.1.20.3
>
> Routing entry for 1.1.20.3/32
>
> Known via "ospf 1", distance 110, metric 1796, type inter area
>
> Last update from 1.1.21.2 on FastEthernet0/1, 00:00:36 ago
>
> Routing Descriptor Blocks:
>
> * 1.1.21.2, from 1.1.8.8, 00:00:36 ago, via FastEthernet0/1
>
> Route metric is 1796, traffic share count is 1
>
>
>
> (after)
>
>
>
> rack1r1#sh ip route 1.1.20.3
>
> Routing entry for 1.1.20.0/24
>
> Known via "ospf 1", distance 110, metric 2, type inter area
>
> Last update from 1.1.21.2 on FastEthernet0/1, 00:00:04 ago
>
> Routing Descriptor Blocks:
>
> * 1.1.21.2, from 1.1.8.8, 00:00:04 ago, via FastEthernet0/1
>
> Route metric is 2, traffic share count is 1
>
>
>
> i.e. here is sw1's config
>
>
>
> rack1sw1#sh run | b router ospf 1
>
> router ospf 1
>
> router-id 1.1.7.7
>
> log-adjacency-changes
>
> area 0 range 1.1.20.0 255.255.255.0
>
> area 331 virtual-link 1.1.3.3 authentication message-digest
>
> area 331 virtual-link 1.1.3.3 message-digest-key 1 md5 cisco
>
> redistribute eigrp 10 subnets tag 188
>
> network 1.1.7.7 0.0.0.0 area 211
>
> network 1.1.11.11 0.0.0.0 area 211
>
> network 1.1.13.1 0.0.0.0 area 331
>
>
>
> Anyone care to comment on this behavior. I was previously unaware virtual
> links endpoints required area range commands for area 0 lsa's we are
> summarizing.
>
>
>
> -Joe
>
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