From: Alex Ouraev (ualexv@gmail.com)
Date: Tue Feb 06 2007 - 00:26:58 ART
Think about this from the service provider's perspective. You need to carry
customer vlans/cdp/vtp unchanged between sites. How would you do that w/o
any knowledge as to how your customer does vlans. The answer is to
encapsulate it again into your own packet with your own tag at the source
switch, then carry it over to the destination customer site, de-capsulate if
you may and spit out unchanged! I don't know who came up with this idea, but
it's simple and brilliant to me... :)
HTH
Alex
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
Mohammad Saeed
Sent: Monday, February 05, 2007 1:07 PM
To: Cisco certification
Subject: dot1q tunnel mode
Hi Evereybody,
When we configure this on an interface on 3550 switch:
switchport trunk encapsulation dot1q
switchport mode trunk
that interface will tag all the frames coming from respective vlans
except the native vlan.
But when we create dot1q tunnel and we configure on one interface that
is connected to Customer site to provide dot1q tunneling:
switchport mode dot1q-tunnel
switchport access-vlan 1000
Now as this port will be receiving traffic from multiple vlans, will
this interface tag all traffic with VLAN ID 1000 (theoratically it
shall not as we are not giving switchport trunk encapsulation dot1q)
or leave the traffic tagged with its original vlan. I am not clear in
what format this interface will receiving the traffic, will that be
normal ethernet frame or ethernet frame tagged with vlan id using
dot1q encapsulation. If any one can expalin a little bit, I will
appreciate that.....
To me it looks like, all traffic will already be encapsulated using
dot1q and this interface will mark those frames with VLAN ID 1000 and
will pass on to other end of dot1q tunnel.....
Regards,
Mohammad Zahed Saeed
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