Portchannel A interface wont go away

Unanswered Question
Jul 8th, 2009

I understand why the A interface for the port channel has been created. It is due to a mismatch and the ones that can be bundled together were put in the A interface. These are LACP etherchannels connected to servers not other switches. Once this is corrected the port channel A interface remains as the active interface and this is causing problems with our paging system since traps appear to come from the 8A interface which is one we can't configure. I'm going to guess we can correct this by doing a shut and no shut on the port channel interface but I would expect there should be a way to move this back to the po4,po6 and po8 interface without taking an outage.

Any ideas?

switch#sh ether 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: 8

Number of aggregators: 11

Group Port-channel Protocol Ports

------+-------------+-----------+-----------------------------------------------

1 Po1(SU) LACP Gi7/2(P) Gi7/4(P)

2 Po2(SU) LACP Gi8/2(P) Gi8/4(P)

3 Po3(SU) LACP Gi6/36(P) Gi12/21(P)

4 Po4(SD) LACP

4 Po4A(SU) LACP Gi6/37(P) Gi11/36(P)

5 Po5(SU) LACP Gi6/38(P) Gi10/25(P)

6 Po6(SD) LACP

6 Po6A(SU) LACP Gi6/40(P) Gi10/24(P)

7 Po7(SU) LACP Gi6/43(P) Gi10/31(P)

8 Po8(SD) LACP

8 Po8A(SU) LACP Gi6/46(P) Gi10/29(P)

I have this problem too.
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johnspaulding Wed, 07/08/2009 - 07:06

From looking at the output there are no interface assigned to the port-channel for P04-8. If you do a show run int gi6/46 for example and look at the channel-group command what does it show for the channel-group name? Does it show the A or just the number.

Giuseppe Larosa Wed, 07/08/2009 - 09:03

Hello Steve,

I had noticed the same behaviour on some C4500 switches here it is my interpretation:

the A stands for automatic or negotiated meaning the bundle is using LACP.

In newer IOS releases this duplication effect has been removed.

I mean this is not a real issue it was a way to communicate that the bundle(s) are using LACP and are negotiated with the other side.

Hope to help

Giuseppe

Eli Barb Thu, 07/16/2009 - 07:22

Secondary Aggregator Ports Po1A or Po2A are Created

A secondary aggregator port will be created in the LACP process when the ports you are

bundling are not compatible with each other, or with their remote peers. The secondary

aggregator port will have the ports which are compatible with others.

Switch#show etherchannel summary

Flags: D - down P - 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

u - unsuitable for bundling

Number of channel-groups in use: 6

Number of aggregators: 8

Group Port-channel Protocol Ports

------+-------------+-----------+-----------------------------------------

1 Po1(SU) LACP Gi1/16(P) Gi10/1(P) Gi10/2(P)

2 Po2(SD) LACP

2 Po2A(SU) LACP Gi1/15(P) Gi10/3(P) Gi10/4(P)

3 Po3(SU) LACP Gi1/14(P) Gi10/5(P) Gi10/6(P)

4 Po4(SD) LACP

4 Po4A(SU) LACP Gi1/13(P) Gi10/7(P) Gi10/8(P)

5 Po5(SU) LACP Gi1/12(P) Gi10/9(P) Gi10/10(P)

6 Po6(SU) LACP Gi1/11(P) Gi10/11(P) Gi10/12(P)

Configure all LAN ports in an EtherChannel to operate at the same speed and in the same

duplex mode. LACP does not support half-duplex. Half-duplex ports in an LACP EtherChannel

are put in the suspended state.

If you configure an EtherChannel from trunking LAN ports, verify that the trunking mode is

the same on all the trunks. LAN ports in an EtherChannel with different trunk modes can

operate unpredictably.

LAN ports with different STP port path costs can form an EtherChannel as long they are

compatibly configured with each other. If you set different STP port path costs, the LAN

ports are not incompatible for the formation of an EtherChannel

Also TAC mentioned the following to me when I had a case with some issues because of this.

Going through the case notes, it seems that another port channel interface

po4a has been created. The information you found is correct. This behavior

is basically a spawned etherchannel, LACP can spawn a secondary portchannel

when there is an incompatible port config, this can only happen in LACP and

it's usually with a misconfiguration of the etherchannel. This is normal

operation of the LACP, it will happen when LACP protocol detects some

inconsistency as per the IEEE 802.3ad standard. Most definitely this should

not impact anything in the network.

The port channel created a spawn port channel .The LACP etherchannels is

functioning correctly as a spawn but to get rid of it, I would suggest you

to schedule a down time and take down the port-channel, put the

configurations to

default, shut the interfaces and recreate both sides and make sure the

configuration is the same in both sides.

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