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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