[j-nsp] LLDP-MED support on EX-series - dot1q trunks

[Doug Hanks]

>From what I understand LLDP don't support the 4-byte tag field in an Ethernet frame.  It should be expecting the EtherType of 0x88cc instead.

Doug

-----Original Message-----
From: juniper-nsp-bounces at puck.nether.net [mailto:juniper-nsp-bounces at puck.nether.net] On Behalf Of Dale Shaw
Sent: Sunday, February 06, 2011 12:07 AM
To: juniper-nsp
Subject: [j-nsp] LLDP-MED support on EX-series - dot1q trunks

Hi all,

I'm a bit confused about LLDP-MED on dot1q trunks.

We have cases where we need to support interfaces connecting to PCs
via an IP phone (typical setup) however the PC is running VMware
Player and the 'guest' operating system's frames are tagged in order
to differentiate them from the host's (it's a software developer
image). We usually use LLDP-MED on access ports when it's just the
phone (tagged) + PC (untagged), and that works well. Aside from
configuring the developer ports as trunks, I'm not aware of a way to
support 2 x tagged + 1 x untagged.

I've observed that LLDP-MED network policy TLVs are not transmitted on
interfaces configured as trunks.

Without having a mad scientist-level understanding of LLDP-MED, I'm
unsure if this is due to lack of support in the protocol itself, a
limitation on EX-series specifically, or what. Couldn't find the
answer in any J or C documentation.

Basic LLDP functionality continues to work fine - we still see the
phones as adjacent - but we need to instruct the phone on which VLAN
ID to use via another mechanism (DHCP in this case).

We're running RSTP and limit the VLANs permitted on such interfaces
but it's still not as elegant as the access+LLDP-MED method.

Cheers,
Dale
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