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Author Topic: Are the Default vlan 1 frames tagged or untagged on trunks  (Read 2592 times)

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Offline scmcdonald

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Are the Default vlan 1 frames tagged or untagged on trunks
« on: June 01, 2015, 10:52:38 AM »
Hi

Can someone tell me if the default vlan 1 frames have an 802.11Q tag on Avaya 5500 switch trunks?

My understanding is that most switches (like CISCO) the default vlan 1 frames  on trunks are untagged. In which case the default vlan1 frames propagate through the network on all trunks as untagged frames.

Similarly, in the Avaya documentation it says that "In the default configuration all incoming packets are assigned VLAN 1 by the default port VLAN identifier (PVID =1). Untagged packets enter *and leave* the switch untagged.

*and leave* i thought implies the same, even though it does not specifically say on trunked ports.


However when I connected a laptop running tcpdump to an Avaya switch 5520 port that had been configured as a trunk with no vlan1 configured on the trunk, I thought I would see these untagged frames but I do not. Or I am doing something wrong.

Can some one please clarify?

thanks
Steve


Offline Telair

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Re: Are the Default vlan 1 frames tagged or untagged on trunks
« Reply #1 on: June 01, 2015, 03:59:06 PM »
VLAN 1 is not a required VLAN on a tagged or untagged port.  If you add VLAN 1 to a tagged port it will show up as a tagged VLAN unless you set it to be the PVID and set the port to untagPvidOnly mode.  Then VLAN 1 would show up as untagged on a tagged port.

But no.  there is no requirement for VLAN 1 to exist at all on Avaya switches.  By default if you reset a switch back to factory, all ports are in VLAN 1 and untagged.  That's what they were talking about in "the default configuration".

Offline Johan Witters

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Re: Are the Default vlan 1 frames tagged or untagged on trunks
« Reply #2 on: June 02, 2015, 03:30:21 AM »
If you define the port as "tagall" the switch will not send out untagged packets on a trunk and will tag all packets, regardless of the pvid.

It will however accept incoming untagged frames, and put it in the vlan marked as pvid on that port. If you don't want that, configure the "filter-untagged-frame" option, in that case all incoming untagged frames will be dropped.

Johan
Kind regards,

Johan Witters

Network Engineer
BKM NV