From: Deepesh Chouhan (deepesh@cisco.com)
Date: Thu Oct 31 2002 - 05:51:42 GMT-3
Hi
I was trying to figure out why authors of dot1q standard added the concept
of untagged traffic. In ISL untagged traffic is not sent or received
Why do we need to untagg traffic ??
<summary>
sw1 is sending packets to sw2 via trunk
sw1-----sw2
On sw1 -
Packets coming from interfaces which are in same vlan as sw1-native vlan,
are untagged and put on trunk
On sw2 -
All untagg packets are fwd. to ports which are in same vlan as sw2-native
vlan
we've to be cautious not to have diff. native vlan, else loops might occur
</summary>
if this is the case why don't we just stop sending untagged traffic, and put
native vlan tag when sending packets over trunk (like ISL). Will make switch
configuration much simpler and less prone to human errors
But assuming untagging is necessary in some cases, shouldn't DTP nego take
care of native vlan mismatch and printout a warning (or in rigid
implementations, fail negotiation process)
thanks
Deepesh
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