My quote was from the RFC, which I believe is the authoritative source.

 All that happens is that a particular bit in the router LSA is set, and
when the two end points agree, based on the V-bit setting and the respective
RID's, the virtual link is established.

Jeff Doyle puts his pants on the same way you and I do. I'm sure he's made a
mistake or two in his life. There are a few pages of errata to be found for
his book. :->

Chuck

-----Original Message-----
From:   Peter I. Slow [mailto:[EMAIL PROTECTED]]
Sent:   Monday, May 28, 2001 10:52 PM
To:     Chuck Larrieu; [EMAIL PROTECTED]
Subject:        Re: Question on the meaning of "tunneling" [7:6136]

" Virtual links are part of the backbone, and behave as if they were
unnumbered point-to-point networks between the two routers. "
its a virtual link. its an unnumbered network. a network/segmrnt
nonetheless, and that description sounds like a tunnel.

it's possible im reading it out of context and misunderstanding....

/ me goes to grab his Doyle book

..Page 464, P1,
"the VL is a tunnel through which packets may be routed on the optimal
pathfrom one endpoint to the other."

...It would be unwise to tell god he is wrong.
Doyle is the man who wrote the book, literally...

----- Original Message -----
From: "Chuck Larrieu" 
To: 
Sent: Tuesday, May 29, 2001 1:18 AM
Subject: RE: Question on the meaning of "tunneling" [7:6136]


> Did some more research. In the context of the question, I went to the RFC
to
> see what the source says. It occurred to me that the behaviour of virtual
> links must be defined in there somewhere.
>
> Sure enough, in the router LSA there is something called the V bit, which
> when set determines that the originator of the LSA is one endpoint of a
> virtual link. when two routers agree that they are the endpoints of the
same
> virtual link, as determined by their RIDs as defined when the VL is
> configured, then the virtual link is established.
>
> "bit V When set, the router is an endpoint of one or more fully adjacent
> virtual links having the described area as Transit area (V is for virtual
> link endpoint)."
>
> In another place:
>
> " Virtual links are part of the backbone, and behave as if they were
> unnumbered point-to-point networks between the two routers. "
>
> I believe this lays to rest the question as to whether of not an OSPF
> virtual link is a tunnel. It is not.
>
> Chuck
>
>
>
> -----Original Message-----
> From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]] On Behalf Of
> Marty Adkins
> Sent: Monday, May 28, 2001 7:24 PM
> To: [EMAIL PROTECTED]
> Subject: Re: Question on the meaning of "tunneling" [7:6136]
>
> "Howard C. Berkowitz" wrote:
> >
> > In the most general sense, a tunnel is a means of taking a protocol
> > data unit payload of OSI layer N of protocol family P1:  (N,P1)-PDU,
> > and transmitting it with a delivery header at layer M of protocol
> > family P2.  What is actually transmitted is, minimally, a (N,P1)-PDU
> > encapsulated in a (M,P2)-PDU.  There may be a "shim" between the end
> > of the delivery header and the beginning of the payload header;
> > there's no good OSIRM term for the shim.
>
> In a slightly less mathematical explanation:
> Think about the encapsulation steps while traveling down the stack.
> Are one or more layers repeated?  If so, then tunneling is involved.
> Yeah, that's simplistic.
>
> - Marty
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