The actual lab I was doing was the Mentor Tech Vlab #4139 - Advanced OSPF.
For those not familiar with either the Vlab advanced lab setups or with the
Slattery/Burton book Advanced TCP/IP Routing the layout is:
Router1-ethernet--Router4
/ \/ \
/ \ / \
/\ / \
Router2 router3--router5 router6
ethernet
Area 0 consisted of routers 4, 5, and 6
Area 1 consisted of routers 1,3, and 5
Area 2 consisted of routers 1 and 2
The router 1-4 link was a non OSPF
So the virtual link / transit was between routers 1 and 5
If the router 5-4 link was shut down from the router 5 side, the virtual
link died. If it was shut down from the router 4 side, the virtual link
remained alive. In other words, even though there was a link to router 5,
the ABR, the fact that the interface connected to area 0 was up or down
difference, whether the loopback ( RID ) was routable or not.
In terms of OSPF behaviour, now that I've gone through the RFC and some
processes are actually making a bit more sense, router5, when it sees the
interface into area 0 go down, immediately does what OSPF demands it do, and
re-populates its OSPF database.
BTW, I'm sure everyone here can now see the flaw in this particular lab.
Practically all of area 0 disappears no matter which side of the link is
shut down. What is insidious is that if the link is broken from the router4
side, the virtual link remains up, even though most of area 0 is not there.
Another example of the pure silliness of the designs of a lot of these CCIE
labs. No one in their right mind would ever do it this way in the real
world. ( well, maybe I can think of a scenario where one might ). But still,
the CCIE lab is not about configuring routers in an effort to get a network
up and running.
I am fortunate in that my employer has a deal with Mentor that give me, in
effect, unlimited access to these labs. I am in the process of acquiring
permission to buy some more. I figure next time I'm in this particular lab,
I'll look at the debugs on router 5 and observe what the RFC tells me should
happen.
Chuck
P.S. in terms of CCIE Lab preparation, the combination of the Slattery book
and a battery of Vlabs might prove worth looking into, particularly if your
employer is willing to spend some money to sponsor your certification
efforts. I'm using the labs as a means of boning up on particular protocols
and behaviours. Later I will be laying out some serious bucks renting rack
time from ccbootcamp as a means of working out their labs.
-Original Message-
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]] On Behalf Of
Nigel Taylor
Sent: Saturday, December 30, 2000 3:06 AM
To: Cisco Group Study; CCIE_Lab Groupstudy List; Chuck Larrieu
Cc: Bryant Andrews
Subject: Revisted - OSPF Virtual Links and RIDs
Chuck,
I finally got a chance to mock this up in the lab and I've
got
some pretty cool resultsFirst of all when I did this using pretty much
the same scenario the virtual link never went down at any time when
the connection to r3 from r2 was shutdown. After clearing the routes
and ospf redistribution the virtual-link was still up/up.
Theory that stood the testI then used a external routing
info.(rip) to advertise routes to the loopback identified with the
virtual-link command. With a direct path/route between both
loopbacks I then shut down the physical link between R1 and R2.
As expected, the virtual-link stayed down and never came back up.
In Doyle's book (Routing TCP/IP) he states that the virtual-link must be
configured between two ABR's and the area it transits must having full
routing info. I take the meaning of this as having a full map of the
network.
There is also a mention of using a non-backbone area, which I also
take to mean - "An OSPF Area" in which case any external routing
info used to obtain a path to the loopback would prove useless if not
part of an OSPF area that is either directly connected to area or
is connected by the same process a virtual-link
Just some observations..
Any thoughts...!
This is some really cool stuff.
Nigel.
- Original Message -
From: Chuck Larrieu <[EMAIL PROTECTED]>
To: CCIE_Lab Groupstudy List <[EMAIL PROTECTED]>
Sent: Sunday, December 24, 2000 1:12 PM
Subject: OSPF Virtual Links and RIDs
> Just got through with one of the multiprotocol redistribution practice
labs
> ( Mentor Labs 4141 )
>
> Got a question regarding virtual links and loopback RIDs.
>
> In the realm of OSPF, when direct ( meaning through the OSPF process )
> access to a particular router is lost, does that mean that any virtual
link
> associated with that router is
