OT: VSS + MEC - port-channel dynamically cloned?
Leland Vandervort
leland at taranta.discpro.org
Tue Nov 24 06:51:29 UTC 2009
Hi all.. this one seems to have stumped even the community forums on
CCO ;) Anyone else seen this behaviour? (It's not actually a problem
as such since the MEC port-channels are actually working fine, just
unexpected the way that it has done it...)
We have a few paris of VSS running, and having brought the down-stream
access-switches online using MEC we note that the active port-channel
that they bind under isn't actually the one configured, but rather a
CLONE of the configured one which appears to be dynamically generated.
In our case, all ports and port-channel configurations are set to dot1q
encapsulation and trunk mode active.
For example, we have about 20 3560s MEC'd to the VSS:
the MEC comes up, but under a slightly different port-channel
identifier:
Here's the 3560 side:
interface status:
Gi0/49 connected trunk a-full a-1000
1000BaseSX SFP
Gi0/50 connected trunk a-full a-1000
1000BaseSX SFP
Gi0/51 connected trunk a-full a-1000
1000BaseSX SFP
Gi0/52 connected trunk a-full a-1000
1000BaseSX SFP
#sh int po1 | i Member
Members in this channel: Gi0/49 Gi0/50 Gi0/51 Gi0/52
Here's the VSS side:
Interface status:
Po11 CISCO C3560 A01 notconnect 1 auto auto
Po11A connected trunk a-full a-1000
^^^^
Po11A is not actually configured, but appears to be cloned from Po11
#sh int po11A | i Member
Members in this channel: Gi1/1/33 Gi1/1/34 Gi2/1/41 Gi2/1/42
#sh cdp nei | i hacc01-d
hacc01-d Gig 2/1/42 140 S I WS-C3560G Gig
0/50
hacc01-d Gig 2/1/41 140 S I WS-C3560G Gig
0/49
hacc01-d Gig 1/1/34 161 S I WS-C3560G Gig
0/52
hacc01-d Gig 1/1/33 161 S | WS-C3560G Gig
0/51
Essentially, for all of the MEC connections, the VSS has created a clone
of the configured port-channel to bind the actual physical connections,
rather than binding them under the configured port-channel (and suffixed
the port-channel number with A or B depending on which chassis was first
to bind).
Config for port-channel and interfaces all match:
VSS SIDE:
interface Port-channel11
description CISCO C3560 A01
switchport
switchport trunk encapsulation dot1q
switchport trunk allowed vlan 40-48,51,400
switchport mode trunk
mtu 9216
end
Physical ports are the same config, with channel-group 11 mode active
(and repeated for 20 different port-channels each with 4 ports)
ACCESS Side:
interface Port-channel1
description DIST-VSS-EQX1
switchport
switchport trunk encapsulation dot1q
switchport trunk allowed vlan 40-48,51,400
switchport mode trunk
mtu 9216
end
Similarly, physical ports are the same with channel-group 1 mode active
I'm not overly worried about it since the MEC is working with the
dynamically generated port-channel, and traffic is flowing correctly...
just curious as to why it uses a clone of the configured port-channel,
rather than the actual configured port-channel itself. Just find that a
bit strange.
Thanks,
Leland
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