From: Bit Gossip (bit.gossip@chello.nl)
Date: Tue Sep 04 2007 - 11:28:11 ART
Experts,
this is the edge port of the sp edge switch (S3) and it is configured with
l2protocol-tunnel:
interface FastEthernet1/0/13
switchport access vlan 101
switchport mode access
speed 100
duplex full
l2protocol-tunnel cdp
l2protocol-tunnel stp
l2protocol-tunnel vtp
l2protocol-tunnel point-to-point lacp
no cdp enable
spanning-tree bpdufilter enable
end
According to:
http://www.cisco.com/univercd/cc/td/doc/product/lan/cat3750/12225see/scg/swtu
nnel.htm
when either a cdp, stp, vtp or lacp frame is received on the tunnel port of
the SP, the frame is tagged dot1q 101 and assigned a COS:
"If a CoS value is configured on the interface for data packets, that value is
the default used for Layer 2 PDUs. If none is configured, the default is 5. "
So I haven't configured cos on f1/0/13 and indeed when I capture the frame on
the trunk on the SP backbone i see cos=5
00:11:93:bb:a2:10 > 01:00:0c:cd:cd:d0, 802.1Q, length 64: vlan 101, p 5, LLC,
dsap STP (0x42), ssap STP (0x42)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Now I want to change it to let's say cos=1, so:
interface FastEthernet1/0/13
mls qos cos 1
mls qos cos override
but nothing changes and still they go out with cos = 5
00:11:93:bb:a2:10 > 01:00:0c:cd:cd:d0, 802.1Q, length 64: vlan 101, p 5, LLC,
dsap STP (0x42), ssap STP (0x42)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Further on in the same doc page: "l2protocol-tunnel cos value:
(Optional) Configure the CoS value for all tunneled Layer 2 PDUs. The range
is 0 to 7; the default is the default CoS value for the interface. If none is
configured, the default is 5."
so I configure it: S2(config)#l2protocol-tunnel cos 1
and, surprise surprise, this works:
00:11:93:bb:a2:10 > 01:00:0c:cd:cd:d0, 802.1Q, length 64: vlan 101, p 1, LLC,
dsap STP (0x42), ssap STP (0x42)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Any idea why the interface level cos setting, case 2, doesn't work?
S2(config)#do show ver
Cisco IOS Software, C3750 Software (C3750-ADVIPSERVICESK9-M), Version
12.2(25)SEE
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