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Channel Group with 2 Port Channels - whats an "A" Channel?

hgans
Level 1
Level 1

Hi!

There is (again) something completely new for me.

A configured Layer 2 Port Channel (channel-group 40) with 2 Ports (Ten2/4, Ten5/4) in it on a 6500 with Sup720.

The strange thing is now there is a Port Channel 40 and also a Port Channel 40A each with 1 Port in it.

The only difference I recognised in the configuration is that "no cdp enable" is configured on one of the channel member ports.

Could this cdp configuration be the cause (cannot test at the moment, since this is critical production environment) for creating a "A" Port Channel?

I expected, that the channel is not built if port members are not configured equal, so I estimate another cause for this unusual situation...

Anyone has an explaination for this?

thanks for any hints!

br.herwig

Group: 40
----------
Group state = L2
Ports: 2   Maxports = 16
Port-channels: 2 Max Port-channels = 16
Protocol:   LACP
Minimum Links: 0

Group  Port-channel  Protocol    Ports
------+-------------+-----------+-----------------------------------------------

40     Po40(SU)        LACP      Te2/4(P)      
40     Po40A(SU)       LACP      Te5/4(P)     

interface Port-channel40
description Layer2_Portchannel
switchport
switchport trunk encapsulation dot1q
switchport mode trunk
switchport nonegotiate
load-interval 30

interface TenGigabitEthernet2/4
description Layer2-Portchannel_
switchport
switchport trunk encapsulation dot1q
switchport mode trunk
switchport nonegotiate
carrier-delay msec 0
udld port aggressive
no cdp enable
channel-group 40 mode active

interface TenGigabitEthernet5/4
description Layer2-Portchannel
switchport
switchport trunk encapsulation dot1q
switchport mode trunk
switchport nonegotiate
carrier-delay msec 0
udld port aggressive
channel-group 40 mode active

router#show etherchannel 40 det
Group state = L2
Ports: 2   Maxports = 16
Port-channels: 2 Max Port-channels = 16
Protocol:   LACP
Minimum Links: 0
                Ports in the group:
                -------------------
Port: Te2/4
------------

Port state    = Up Mstr In-Bndl
Channel group = 40          Mode = Active      Gcchange = -
Port-channel  = Po40        GC   =   -         Pseudo port-channel = Po40
Port index    = 0           Load = 0xFF        Protocol =   LACP

Flags:  S - Device is sending Slow LACPDUs   F - Device is sending fast LACPDUs.
        A - Device is in active mode.        P - Device is in passive mode.

Local information:
                            LACP port     Admin     Oper    Port        Port
Port      Flags   State     Priority      Key       Key     Number      State
Te2/4     SA      bndl      32768         0x28      0x28    0x205       0x3D

Partner's information:

          Partner Partner   LACP Partner  Partner   Partner  Partner     Partner
Port      Flags   State     Port Priority Admin Key Oper Key Port Number Port State
Te2/4     SA      bndl      32768         0x0       0x28     0x205       0x3D

Age of the port in the current state: 3d:21h:55m:11s

Port: Te5/4
------------

Port state    = Up Mstr In-Bndl
Channel group = 40          Mode = Active      Gcchange = -
Port-channel  = Po40A       GC   =   -         Pseudo port-channel = Po40
Port index    = 0           Load = 0xFF        Protocol =   LACP

Flags:  S - Device is sending Slow LACPDUs   F - Device is sending fast LACPDUs.
        A - Device is in active mode.        P - Device is in passive mode.

Local information:
                            LACP port     Admin     Oper    Port        Port
Port      Flags   State     Priority      Key       Key     Number      State
Te5/4     SA      bndl      32768         0x28      0x28    0x505       0x3D

Partner's information:

          Partner Partner   LACP Partner  Partner   Partner  Partner     Partner
Port      Flags   State     Port Priority Admin Key Oper Key Port Number Port State
Te5/4     SA      bndl      32768         0x0       0x1028   0x505       0x3D

Age of the port in the current state: 3d:21h:55m:11s

                Port-channels in the group:
                ----------------------

Port-channel: Po40    (Primary Aggregator)

------------

Age of the Port-channel   = 346d:06h:32m:02s
Logical slot/port   = 14/8          Number of ports = 1
HotStandBy port = null
Port state          = Port-channel Ag-Inuse
Protocol            =   LACP
Fast-switchover     = disabled
Load share deferral = disabled 

Ports in the Port-channel:

Index   Load   Port     EC state        No of bits
------+------+------+------------------+-----------
  0     FF     Te2/4    Active    8

Time since last port bundled:    3d:21h:55m:11s    Te2/4
Time since last port Un-bundled: 3d:21h:55m:17s    Te5/4

Port-channel: Po40A
------------

Age of the Port-channel   = 3d:21h:55m:18s
Logical slot/port   = 14/6          Number of ports = 1
HotStandBy port = null
Port state          = Port-channel Ag-Inuse
Protocol            =   LACP
Fast-switchover     = disabled
Load share deferral = disabled 

Ports in the Port-channel:

Index   Load   Port     EC state        No of bits
------+------+------+------------------+-----------
  0     FF     Te5/4    Active    8

Time since last port bundled:    3d:21h:55m:13s    Te5/4

Last applied Hash Distribution Algorithm: Fixed

2 Replies 2

Jayakrishna Mada
Cisco Employee
Cisco Employee

Hi Hgans,

See if this links helps you:

http://www.cisco.com/en/US/tech/tk389/tk213/technologies_configuration_example09186a0080094470.shtml#po1a

Usually its recommended to configure all the ports with the same configuration, sometimes it does allow you to form a port-channel but you will see such secondary port-channel formed.

Are linecards 2 and 5 same model linecards ?

JayaKrishna.

Hi,

hmm, interesting.

we have a second pair of 65k with similar channel setup under same IOS and hardware.

on these boxes I don't see this "sub" channels.

So at the moment I think the cause is indeed the "no cdp enable" configuration on one of the two member ports.

I will eliminate the cdp configuration in my next maintenance window and state a result here....

This are the Modules that form the channel:

2    8  CEF720 8 port 10GE with DFC            WS-X6708-10GE

5    5  Supervisor Engine 720 10GE (Active)    VS-S720-10G

Herwig

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