If they allow vlan 50 into your trunk port, then THAT traffic will hit your switch but will get dumped by your switch if you do NOT allow vlan 50; and I believe the vlan 50 packets are counted as DISCARDED frames on that port. So the pipe is more congested with vlan 50 traffic. (That is packets that are non-unicast and unknown-unicast).
Jeff Fitzwater Princeton University On Sep 21, 2011, at 11:48 , null zeroroute wrote: > I have an 8021q trunk link that permits 3 out of 20 VLAN's. The trunk port > permits VLAN ID's 2,3,4, and uses native VLAN 25. The VLAN ID's in the > local VTP domain are 5-25. There are no other VLAN's in the switched domain > at the location in question. There are no other switchports in VLAN 25. > > The trunk port is connected to a WAN service provider layer2 device, which > is connected to a VPLS service. > > If the service provider sends a frame onto the trunk port tagged with VLAN > ID 50, will my trunk port accept the frame and forward it "somewhere" or > will it drop the frame? > > Note that VLAN 50 does not exist at the location in question, there are no > ports in that VLAN. > > So the question I have is... How does the "switchport trunk allowed vlan" > command affect forwarding from an inbound perspective? > > If "switchport trunk allowed vlan" doesn't prevent a VLAN tagged frame from > being accepted into a network, is there any way to prevent a VLAN tagged > frame from entering your network that shouldn't be? > > The reason I ask is because I have a situation where the trunkport is > accepting the frame that I assume it shouldn't, forwarding into my network, > and a loop ensues. That loop is a differnet issue all together I think. My > main question is about the behavior of "switchport trunk allowed vlan" as it > relates to inbound and outbound forwarding. I have no idea why VLAN's > tagged with VLAN 50 are entering my network and getting forwarded around. I > know those frames are entering my network at this location because I see the > 8021q header in wireshark. > > Thanks, > > --NZR > _______________________________________________ > cisco-nsp mailing list [email protected] > https://puck.nether.net/mailman/listinfo/cisco-nsp > archive at http://puck.nether.net/pipermail/cisco-nsp/ _______________________________________________ cisco-nsp mailing list [email protected] https://puck.nether.net/mailman/listinfo/cisco-nsp archive at http://puck.nether.net/pipermail/cisco-nsp/
