Cisco 887 router LAN or Cisco switch port shown as down, down?

Yet another ‘unusual’ Cisco IOS Ethernet port issue – you’d almost think I bring this on myself by having a complicated home network!

I was configuring a Cisco 887VA-M on my home network and had finished so I plugged the FastEthernet0 port into my underdesk Cisco 2960X so it was part of the LAN.

On the connected console to the 887 I noticed
*Nov  9 14:38:23.303: %LINK-3-UPDOWN: Interface FastEthernet0, changed state to down
*Nov  9 14:38:56.947: %LINK-3-UPDOWN: Interface FastEthernet0, changed state to down
*Nov  9 14:39:29.127: %LINK-3-UPDOWN: Interface FastEthernet0, changed state to down
*Nov  9 14:40:01.179: %LINK-3-UPDOWN: Interface FastEthernet0, changed state to down
*Nov  9 14:40:33.307: %LINK-3-UPDOWN: Interface FastEthernet0, changed state to down
*Nov  9 14:41:05.595: %LINK-3-UPDOWN: Interface FastEthernet0, changed state to down
*Nov  9 14:41:37.479: %LINK-3-UPDOWN: Interface FastEthernet0, changed state to down

eh?

Down messages but no up message. Lets look at the interfaces on the box:

887VAM_RR:#sh ip int br
*Nov  9 14:42:09.687: %LINK-3-UPDOWN: Interface FastEthernet0, changed state to down
Any interface listed with OK? value “NO” does not have a valid configuration

Interface                  IP-Address      OK? Method Status                Protocol
ATM0                       unassigned      YES manual down                  down
Dialer1                    unassigned      YES manual up                    up
Ethernet0                  unassigned      YES unset  administratively down down
FastEthernet0              unassigned      YES unset  down                  down
FastEthernet1              unassigned      YES unset  down                  down
FastEthernet2              unassigned      YES unset  down                  down
FastEthernet3              unassigned      YES unset  down                  down
NVI0                       unassigned      NO  unset  up                    up
Virtual-Access1            unassigned      YES unset  up                    up
Vlan1                      192.168.70.253  YES manual down                  down

Change the cable. No difference.

Try another port on the 887. No difference.

Try another port on the 2960X. No difference.

Nothing special listed when I look at the FastEthernet interface on the router:

887VAM_RR:#sh int faste0
FastEthernet0 is down, line protocol is down

or the VLAN interface:

887VAM_RR:#sh int vlan1
Vlan1 is down, line protocol is down

Is the router damaged? – No

Is there an issue with the FastEthernet controller? – No

Dodgy VLAN.DAT file in the flash? – No

Is the FastEthernet0 interface not part of VLAN1:

887VAM_RR:#sh vlan-switch

VLAN Name                             Status    Ports
—- ——————————– ———
1    default                                 active    Fa0, Fa1, Fa2, Fa3

No issue there then.

Reload, that will work. No difference.

Speed, Duplex – I am clutching at straws now. Nothing seems amiss and nothing works regardless of what values I set.

Nothing found in Google that is relevant (hence why I am writing this article to help you, the reader, out if it happens to you)

Reload again.

Hey what’s this?

*Nov  9 15:25:03.383: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0, changed state to down
*Nov  9 15:25:03.383: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet1, changed state to down
*Nov  9 15:25:03.383: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet2, changed state to down
*Nov  9 15:25:03.383: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet3, changed state to down
*Nov  9 15:25:05.915: %CDP-4-DUPLEX_MISMATCH: duplex mismatch discovered on FastEthernet0 (not half duplex), with Switch GigabitEthernet1/0/4 (half duplex).
*Nov  9 15:25:07.143: %LINK-3-UPDOWN: Interface FastEthernet0, changed state to down
*Nov  9 15:25:42.375: %LINK-3-UPDOWN: Interface FastEthernet0, changed state to down

So my router can see across the Ethernet link to the other side. What is going on!

887VAM_RR:>sh cdp ne
Capability Codes: R – Router, T – Trans Bridge, B – Source Route Bridge
                  S – Switch, H – Host, I – IGMP, r – Repeater, P – Phone,
                  D – Remote, C – CVTA, M – Two-port Mac Relay

Device ID        Local Intrfce     Holdtme    Capability  Platform  Port ID
Switch           Fas 0              139            R S I  WS-C2960X Gig 1/0/4

so I can see the other side. Yet still with the messages:

*Nov  9 15:25:07.143: %LINK-3-UPDOWN: Interface FastEthernet0, changed state to down
*Nov  9 15:25:42.375: %LINK-3-UPDOWN: Interface FastEthernet0, changed state to down

Where is the other side gone now?!

887VAM_RR:#sh cdp nei
Capability Codes: R – Router, T – Trans Bridge, B – Source Route Bridge
                  S – Switch, H – Host, I – IGMP, r – Repeater, P – Phone,
                  D – Remote, C – CVTA, M – Two-port Mac Relay

Device ID        Local Intrfce     Holdtme    Capability  Platform  Port ID

Right let’s plug in a laptop to the Ethernet port instead:

*Nov  9 16:06:42.543: %LINK-3-UPDOWN: Interface FastEthernet0, changed state to up
*Nov  9 16:06:43.543: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0, changed state to up
*Nov  9 16:07:11.563: %LINEPROTO-5-UPDOWN: Line protocol on Interface Vlan1, changed state to up

Boom!

So it must be the other end causing the issue. Then I notice that the other end never had a link light. I never noticed because the 2960X is under the desk.

Then it dawns on me. I set the ports on the 2960X to bpduguard to make sure that if I plug in a switch it doesn’t cause a spanning tree loop. That is why the port doesn’t come up on the Ethernet 877 router because the LAN ports are actually 4 switch ports. Doh!

Checking the log on the 2960X shows:

000723: Nov  9 15:53:07.620: %PM-4-ERR_DISABLE: bpduguard error detected on Gi1/0/6, putting Gi1/0/6 in err-disable state
000724: Nov  9 15:53:37.616: %PM-4-ERR_RECOVER: Attempting to recover from bpduguard err-disable state on Gi1/0/6
000725: Nov  9 15:53:39.629: %SPANTREE-2-BLOCK_BPDUGUARD: Received BPDU on port Gi1/0/6 with BPDU Guard enabled. Disabling port.
000726: Nov  9 15:53:39.629: %PM-4-ERR_DISABLE: bpduguard error detected on Gi1/0/6, putting Gi1/0/6 in err-disable state
000727: Nov  9 15:54:09.618: %PM-4-ERR_RECOVER: Attempting to recover from bpduguard err-disable state on Gi1/0/6
000728: Nov  9 15:54:11.646: %SPANTREE-2-BLOCK_BPDUGUARD: Received BPDU on port Gi1/0/6 with BPDU Guard enabled. Disabling port.

so that explains why the port on the router goes down every 30 seconds or so, I had autorecovery set on the 2960X, so it would bring the port back up, see the BPDU from the router LAN switch ports and disable the Ethernet port facing the router again.

interface GigabitEthernet1/0/6
 switchport mode access
 spanning-tree portfast
 spanning-tree bpduguard enable

easily fixed with

Switch(config-if)#no spanning-tree bpduguard

3,2,1, fix the duplex issue, and we are back in action and I can get on and configure the ATM/Dialer1 interface.

so next time you see

%LINK-3-UPDOWN: Interface FastEthernet0, changed state to down

maybe it will be the other end that needs to be sorted.

 

 

 

 

 

 

 

 

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