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「channel-misconfig error detected」エラー時の対処

両端の Catalyst スイッチで EtherChannel 設定変更時に、インターフェイスが err-disable となってしまった場合の復旧方法についてメモしておきます。

事象

EtherChannel では両端の設定が不一致だと、インターフェイスが err-disable 状態となり、Port-channel インターフェイスはリンクアップしません。今回は対向側が "channel-group 14 mode desirable" と、自スイッチが "channel-group 14 mode on" となっている為、設定上の不一致が発生しています。

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Rack1SW4#
Mar  6 16:04:08.283: %LINK-3-UPDOWN: Interface Port-channel14, changed state to up
Mar  6 16:04:09.283: %LINEPROTO-5-UPDOWN: Line protocol on Interface Port-channel14, changed state to up
Rack1SW4#
Mar  6 16:04:43.167: %PM-4-ERR_DISABLE: channel-misconfig error detected on Po14, putting Fa0/13 in err-disable state
Mar  6 16:04:43.183: %PM-4-ERR_DISABLE: channel-misconfig error detected on Po14, putting Fa0/14 in err-disable state
Mar  6 16:04:43.195: %PM-4-ERR_DISABLE: channel-misconfig error detected on Po14, putting Fa0/15 in err-disable state
Mar  6 16:04:43.223: %PM-4-ERR_DISABLE: channel-misconfig error detected on Po14, putting Po14 in err-disable state
Rack1SW4#
Mar  6 16:04:44.171: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/13, changed state to down
Mar  6 16:04:44.183: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/14, changed state to down
Mar  6 16:04:44.199: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/15, changed state to down
Mar  6 16:04:44.207: %LINEPROTO-5-UPDOWN: Line protocol on Interface Port-channel14, changed state to down
Rack1SW4#
Mar  6 16:04:45.183: %LINK-3-UPDOWN: Interface FastEthernet0/13, changed state to down
Mar  6 16:04:45.195: %LINK-3-UPDOWN: Interface FastEthernet0/14, changed state to down
Mar  6 16:04:45.219: %LINK-3-UPDOWN: Interface Port-channel14, changed state to down
Mar  6 16:04:45.223: %LINK-3-UPDOWN: Interface FastEthernet0/15, changed state to down

Port-channel インターフェイスがリンクアップすることを期待し、自スイッチ側を "channel-group 14 mode auto" とします。

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Rack1SW4# configure terminal 
Enter configuration commands, one per line.  End with CNTL/Z.
Rack1SW4(config)# interface range FastEthernet 0/13 - 15
Rack1SW4(config-if-range)# channel-group 14 mode auto

しかし、やはりリンクアップしません...

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Rack1SW4# show interfaces status | include Fa0/1[3-5]|Po14
Fa0/13                       err-disabled 1            auto   auto 10/100BaseTX
Fa0/14                       err-disabled 1            auto   auto 10/100BaseTX
Fa0/15                       err-disabled 1            auto   auto 10/100BaseTX
Po14                         err-disabled 1            auto   auto

err-disable 状態は通常、該当インターフェイスを "shutdown" / "no shutdown" することで解消します。まずは、物理インターフェイスを "shutdown" します。

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Rack1SW4# configure terminal 
Enter configuration commands, one per line.  End with CNTL/Z.
Rack1SW4(config)# interface range FastEthernet 0/13 - 15
Rack1SW4(config-if-range)# shutdown 
Rack1SW4(config-if-range)#
Mar  6 16:12:34.715: %LINK-5-CHANGED: Interface FastEthernet0/13, changed state to administratively down
Mar  6 16:12:34.723: %LINK-5-CHANGED: Interface FastEthernet0/14, changed state to administratively down
Mar  6 16:12:34.731: %LINK-5-CHANGED: Interface FastEthernet0/15, changed state to administratively down

続けて、すぐに "no shutdown" します。しかし、すぐに err-disable 状態へ戻ってしまいます...

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Rack1SW4(config-if-range)# no shutdown 
Rack1SW4(config-if-range)#
Mar  6 16:12:40.331: %PM-4-ERR_DISABLE: channel-misconfig error detected on Fa0/13, putting Fa0/13 in err-disable state
Mar  6 16:12:40.371: %PM-4-ERR_DISABLE: channel-misconfig error detected on Fa0/14, putting Fa0/14 in err-disable state
Mar  6 16:12:40.491: %PM-4-ERR_DISABLE: channel-misconfig error detected on Fa0/15, putting Fa0/15 in err-disable state
Rack1SW4(config-if-range)#
Mar  6 16:12:40.815: %LINK-3-UPDOWN: Interface FastEthernet0/13, changed state to down
Mar  6 16:12:40.835: %LINK-3-UPDOWN: Interface FastEthernet0/14, changed state to down
Mar  6 16:12:40.859: %LINK-3-UPDOWN: Interface FastEthernet0/15, changed state to down

対処方法

このような場合（Port-channel 自体が err-disable になってしまった場合は）EtherChannel を構成する物理メンバー（＝物理インターフェイス）ではなく、Port-channel インターフェイス自体で "shutdown" / "no shutdown" を実行します。

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Rack1SW4(config-if-range)# exit
Rack1SW4(config)#
Rack1SW4(config)# interface Port-channel 14
Rack1SW4(config-if)# shutdown 
Rack1SW4(config-if)#
Mar  6 16:17:03.843: %LINK-5-CHANGED: Interface FastEthernet0/13, changed state to administratively down
Mar  6 16:17:03.843: %LINK-5-CHANGED: Interface FastEthernet0/14, changed state to administratively down
Mar  6 16:17:03.847: %LINK-5-CHANGED: Interface FastEthernet0/15, changed state to administratively down
Mar  6 16:17:03.847: %LINK-5-CHANGED: Interface Port-channel14, changed state to administratively down
Rack1SW4(config-if)# no shutdown 
Rack1SW4(config-if)#
Mar  6 16:17:12.535: %LINK-3-UPDOWN: Interface Port-channel14, changed state to down
Mar  6 16:17:12.535: %LINK-3-UPDOWN: Interface FastEthernet0/13, changed state to up
Mar  6 16:17:12.535: %LINK-3-UPDOWN: Interface FastEthernet0/14, changed state to up
Mar  6 16:17:12.539: %LINK-3-UPDOWN: Interface FastEthernet0/15, changed state to up
Rack1SW4(config-if)#
Mar  6 16:17:18.027: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/15, changed state to up
Mar  6 16:17:18.875: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/13, changed state to up
Mar  6 16:17:18.975: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/14, changed state to up
Rack1SW4(config-if)#
Mar  6 16:17:19.015: %LINK-3-UPDOWN: Interface Port-channel14, changed state to up
Rack1SW4(config-if)#
Mar  6 16:17:20.015: %LINEPROTO-5-UPDOWN: Line protocol on Interface Port-channel14, changed state to up

これで無事、Port-channel インターフェイスがリンクアップしました。