EtherChannel Question

jezg76

Greetings all.

Studying hard on the BCMSN part on the CCNP trek and I was peeking around our work switches and noticed something odd with regards to the output of some show commands...

Quick ascii of the topology in question:

6509                      3750
Gi8/7 ------------------- 3/0/49
Gi8/8 ------------------- 1/0/49

There is MMF fiber linking these two devices and the links are configured as a an EtherChannel as such:

6509

interface GigabitEthernet8/7
 description link to Zone 2.1
 switchport
 switchport trunk encapsulation dot1q
 switchport mode trunk
 no ip address
 channel-group 2 mode active
end
!
interface GigabitEthernet8/8
 description link to Zone 2.2
 switchport
 switchport trunk encapsulation dot1q
 switchport mode trunk
 no ip address
 channel-group 2 mode active
end

3750

interface GigabitEthernet1/0/49
 description *** UPLINK TO CORE G8/8 ***
 switchport trunk encapsulation dot1q
 switchport mode trunk
 channel-group 2 mode active
end
!
interface GigabitEthernet3/0/49
 description *** UPLINK TO CORE G8/7 ***
 switchport trunk encapsulation dot1q
 switchport mode trunk
 channel-group 2 mode active
end

The output of the show etherchannel summary

6509

Z1-C6509-D-01#show etherchannel summary
Flags:  D - down        P - bundled in port-channel
        I - stand-alone s - suspended
        H - Hot-standby (LACP only)
        R - Layer3      S - Layer2
        U - in use      f - failed to allocate aggregator

        M - not in use, minimum links not met
        u - unsuitable for bundling
        w - waiting to be aggregated
Number of channel-groups in use: 2
Number of aggregators:           2

Group  Port-channel  Protocol    Ports
------+-------------+-----------+-----------------------------------------------
2      Po2(SU)         LACP      Gi8/7(P)   Gi8/8(P)
10     Po10(RD)         -

3750

Z2-C3750-D-01#show etherchannel summary
Flags:  D - down        P - bundled in port-channel
        I - stand-alone s - suspended
        H - Hot-standby (LACP only)
        R - Layer3      S - Layer2
        U - in use      f - failed to allocate aggregator

        M - not in use, minimum links not met
        u - unsuitable for bundling
        w - waiting to be aggregated
        d - default port


Number of channel-groups in use: 1
Number of aggregators:           1

Group  Port-channel  Protocol    Ports
------+-------------+-----------+-----------------------------------------------
2      Po2(SU)         LACP      Gi1/0/49(P) Gi3/0/49(P)

Seems all is working as configured, but here is what is messing with my dome. The output of the show etherchannel port-channel command:

6509

Z1-C6509-D-01#sh ether port-channel
                Channel-group listing:
                -----------------------

Group: 2
----------
                Port-channels in the group:
                ----------------------

Port-channel: Po2    (Primary Aggregator)

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

Age of the Port-channel   = 195d:03h:10m:44s
Logical slot/port   = 14/1          Number of ports = 2
Port state          = Port-channel Ag-Inuse
Protocol            =   LACP

Ports in the Port-channel:

Index   Load   Port     EC state        No of bits
------+------+------+------------------+-----------
  0     55     Gi8/7    Active    4
  1     AA     Gi8/8    Active    4

Time since last port bundled:    195d:03h:09m:53s    Gi8/8

3750

Z2-C3750-D-01#sh ether port-channel
                Channel-group listing:
                ----------------------

Group: 2
----------
                Port-channels in the group:
                ---------------------------

Port-channel: Po2    (Primary Aggregator)

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

Age of the Port-channel   = 253d:01h:23m:48s
Logical slot/port   = 10/2          Number of ports = 2
HotStandBy port = null
Port state          = Port-channel Ag-Inuse
Protocol            =   LACP
Port security       = Disabled

Ports in the Port-channel:

Index   Load   Port     EC state        No of bits
------+------+------+------------------+-----------
  0     00     Gi1/0/49 Active             0

Time since last port bundled:    195d:03h:12m:56s    Gi1/0/49
Time since last port Un-bundled: 195d:03h:43m:51s    Gi3/0/49

Does the fact that the 3750 is in a stacked configuration cause this funkiness or is there an underlying issue?

Thanks for your time!

Netstudent

It looks more like a bug to me or the cross-stack config is not supported. What version code are you running? I would check the bug tracker just to be sure.

I have a stack of 3750G's with an etherchannel trunk to the core 6509 that I brought up last week. Here is my output on the stack. only difference between you and I is I used the ON keyword and you used the ACTIVE keyword and I have my links on the same unit. With the ON keyword there is no exchange of LACP parameters so I'm wondering if you have an LACP bug or a stackwise issue or possible not a feature. But then again I have never implemented a cross-stack bundle like that. But I know that cross-stack LACP is only supported on images 12.2(25)SEC and later. With a cross-stack config, try using the ON keyword to manually force it to an etherchannel.

But thats a good catch on your part.

Collo_Stack#show ether port-channel
                Channel-group listing:
                ----------------------

Group: 1
----------
                Port-channels in the group:
                ---------------------------

Port-channel: Po1
------------

Age of the Port-channel   = 6d:17h:38m:57s
Logical slot/port   = 10/1          Number of ports = 2
GC                  = 0x00000000      HotStandBy port = null
Port state          = Port-channel Ag-Inuse
Protocol            =    -

Ports in the Port-channel:

Index   Load   Port     EC state        No of bits
------+------+------+------------------+-----------
  0     00     Gi1/0/23 On                 0
  0     00     Gi1/0/24 On                 0

Time since last port bundled:    6d:17h:37m:31s    Gi1/0/23

AND 6509

Franklin_Colo#show ether port-channel
                Channel-group listing:
                -----------------------

Group: 1
----------
                Port-channels in the group:
                ----------------------

Port-channel: Po1
------------

Age of the Port-channel   = 6d:19h:07m:11s
Logical slot/port   = 14/1          Number of ports = 2
GC                  = 0x00000000      HotStandBy port = null
Port state          = Port-channel Ag-Inuse
Protocol            =    -

Ports in the Port-channel:

Index   Load   Port     EC state        No of bits
------+------+------+------------------+-----------
  1     55     Gi3/45   On    4
  0     AA     Gi3/46   On    4

jezg76

The stacked 3750 has the following image file: c3750-ipbasek9-mz.122-40.SE.bin.

I will do some more investigative reports and test some things in the off-hour.

Thanks for your reply.

EdTheLad

I wouldnt worry too much,there are so many bugs on cisco ios related to etherchannels you wouldn't believe.

jezg76

And a bug it is.

==============================================================
Hello Jeremi,

I confirmed the behavior you observed based on the output you provided.
As this looked like a software bug I started to search for known issues
and was able to match your symptoms to a known bug, namely
CSCsj62772. Due to this bug only participating ports in the stack master
are displayed.
Bug Details:

Symptom:
Issue with the cross stack etherchannel. The etherchannel CLI fails to
show active etherchannel members of a cross stack etherchannel that
are located on slave switches. The CLI "show etherchannel summary"
correctly shows all members. In the output of this command description
of only interface:1 is seen and description of interface:2 and 3 is missing.

Conditions:
Problem is seen only in case of cross-stack etherchannel. i.e. some
members of EC on master and some on slaves too.

Workaround:
No workaround.

Further Problem Description:
After creating a cross-stack EC. E.G. interface:1 on master, interface:2
on slave1, interface:3 on slave2 we need to issue <CmdBold> show
etherchannel port-channel <noCmdBold> CLI. Though this is a display
issue yet this might impact troubleshooting as the show command helps
us to gain information about the etherchannel.

There is a fix for CSCsj62772 included in the 12.2(44)SE release, which
is already available on CCO.
==============================================================

Thanks guys.