Tunneling, in general, is taking data (whether user data, routing
information, etc), encapsulating it in another protocol for travel (i.e.
TCP/IP), and sending it to a destination where the other end unwraps the
encapsulation and then uses the data (whether user data, routing
information, etc). DONE!
It's obvious that the quotes below are written specifically talking about
OSPF Virtual Links, which basically is for routing formation only. However,
DLSW tunnels, STUN and BSTUN tunnels simply take the SNA (or Sync or Bi-Sync
serial) frames, encapsulate them in IP packets, route them through the
internetwork, and then gets rid of the IP encapsulation and uses the
SNA/Synch/Bi-Synch frames as they were transmitted from the original source.
DLSW is a major tunneling system used to connect mainframes because you can
stick a router on the token ring connected to each mainframe, and as long as
there is an IP route between the 2 routers (and they know each others IP
address), they establish a tunnel, and the two mainframes think they're
directly connected (actually they think they're on rings that are
connected).
On another note, the statement that "there is no physical/datalink"
connectivity, although true, is kinda misleading. In the case of DLSW
tunnels, the routers on either end of the tunnel use TCP to provide reliable
transport of the SNA traffic, and then use Local Acknowledgement to each of
the mainframes, thus providing "virtual" datalink connectivity. As far as
the mainframes are concerned, there IS a datalink connection.
So, you must realize, in OSPF Virtual Links, the tunneling process only
carries routing data, but other tunnels DO carry application data....
Mike W.
"Chuck Larrieu" wrote in message
[EMAIL PROTECTED]">news:[EMAIL PROTECTED]...
> Question came up on the CCIE group revolving around the meaning of the
term
> "tunnel"
>
> I think I am seeing where the author of the below quote is going. I'm
> wondering if one of the folks on this group might be willing to offer some
> insight.
>
> The question originated with someone calling an OSPF virtual link a
tunnel.
> After some back and forth, someone offered the following (edited for
> brevity, and clarity):
>
> "...understand the basics of software tunneling. TUNNELING PROVIDES
> ALTERNATIVE TO THE NATIVE CONNECTIVITY PROCEDURE. In this case there is no
> physical/datalink connectivity, so connectivity is achieved through
software
> interface.
>
> " Virtual Links are not tunnels, you can't transport traffic over them,
they
> just carry routing information. They are TUNNELING this routing
information
> through area 1. THIS IS THE PRINCIPLE OF TUNNELLING. IT IS NOT ONLY
> APPLICATION DATA THAT IS TUNNELED : IN THIS CASE ROUTING UPDATES ARE BEING
> TUNNELED!
>
> "you seem to know only Cisco exam material (tunnel interfaces) please read
> further afield and grasp generics/basics of software programming
principles,
> "
>
> Can anyone offer further clarification here?
>
> Thanks
>
> Chuck
>
> One IOS to forward them all.
> One IOS to find them.
> One IOS to summarize them all
> And in the routing table bind them.
>
> -JRR Chambers-
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