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New Member

Switch repeatedly loses connection

Hi guys,

I have a 3750 switch that repeated loses connection several times a day. It would be up for hours and then drop in and out for several minutes during which you totally lose connection to it. Even devices within the same subnet are unable to connect to it.

Any ideas why and what to check for? The uptime shows the router does not actually go down and there is nothing in the log.

See below the sh ver output and the logs in the syslog server.

switch1#sh ver

Cisco IOS Software, C3750 Software (C3750-IPSERVICES-M), Version 12.2(25)SEB4, RELEASE SOFTWARE (fc1

)

Copyright (c) 1986-2005 by Cisco Systems, Inc.

Compiled Tue 30-Aug-05 15:47 by yenanh

ROM: Bootstrap program is C3750 boot loader

BOOTLDR: C3750 Boot Loader (C3750-HBOOT-M) Version 12.1(14r)EA1a, RELEASE SOFTWARE (fc1)

switch1 uptime is 1 year, 8 weeks, 5 days, 15 hours, 49 minutes

System returned to ROM by power-on

Syslog

Alert: switch1.hwph.nhs.uk is Down. 06:06

Reset: switch1.hwph.nhs.uk is Up 05:37

Alert: switch1.hwph.nhs.uk is Down. 05:31

Reset: switch1.hwph.nhs.uk is Up 05:17

Alert: switch1.hwph.nhs.uk is Down. 05:11

Reset: switch1.hwph.nhs.uk is Up 04:55

Alert: switch1.hwph.nhs.uk is Down. 04:37

Reset: switch1.hwph.nhs.uk is Up 04:24

...................

....................

...................

Any assistance is much appreciated.

Cheers,

Martha.

8 REPLIES

Re: Switch repeatedly loses connection

Martha,

Start looking at SPT flaps:

"sh spanning-tree vlan X detail | inc last" will show if STP is an issue.

also, make sure no debugging is enable annd take a look at CPU history if possible. If CPU is spiking for some reason it would affect vital process like advertising routing.

Another possibility is uplink utilisation.

HTH

Sam

New Member

Re: Switch repeatedly loses connection

Hi Sam,

Thanks for your prompt response.

I have checked and there is definitely no debugging on the switch.

See output of other commands below.

I could not remotely access the switch during the outage so I have not got the cpu utilization for that period.

switch1#sh spanning-tree vlan 200 detail | i last

Number of topology changes 1 last change occurred 5d16h ago

switch1#sh spanning-tree vlan 200 detail

VLAN0200 is executing the rstp compatible Spanning Tree protocol

Bridge Identifier has priority 32768, sysid 200, address 0018.1855.4500

Configured hello time 2, max age 20, forward delay 15

We are the root of the spanning tree

Topology change flag not set, detected flag not set

Number of topology changes 1 last change occurred 5d16h ago

from StackPort1

Times: hold 1, topology change 35, notification 2

hello 2, max age 20, forward delay 15

Timers: hello 0, topology change 0, notification 0, aging 300

switch1#sh spanning-tree vlan 200 detail

Port 22 (GigabitEthernet1/0/22) of VLAN0200 is designated forwarding

Port path cost 4, Port priority 128, Port Identifier 128.22.

Designated root has priority 33221, address 0018.1855.4500

Designated bridge has priority 33221, address 0018.1855.4500

Designated port id is 128.22, designated path cost 0

Timers: message age 0, forward delay 0, hold 0

Number of transitions to forwarding state: 1

The port is in the portfast mode

Link type is point-to-point by default

BPDU: sent 560, received 0

Port 64 (GigabitEthernet2/0/12) of VLAN0200 is designated forwarding

Port path cost 19, Port priority 128, Port Identifier 128.64.

Designated root has priority 33221, address 0018.1855.4500

Designated bridge has priority 33221, address 0018.1855.4500

Designated port id is 128.64, designated path cost 0

Timers: message age 0, forward delay 0, hold 0

Number of transitions to forwarding state: 1

The port is in the portfast mode

Link type is shared by default

BPDU: sent 87762, received 0

Port 74 (GigabitEthernet2/0/22) of VLAN0200 is designated forwarding

Port path cost 19, Port priority 128, Port Identifier 128.74.

Designated root has priority 33221, address 0018.1855.4500

Designated bridge has priority 33221, address 0018.1855.4500

Designated port id is 128.74, designated path cost 0

Timers: message age 0, forward delay 0, hold 0

Number of transitions to forwarding state: 1

The port is in the portfast mode

Link type is point-to-point by default

BPDU: sent 72906, received 0

Cheers,

Martha.

Re: Switch repeatedly loses connection

SPT looks stable, for cpu can you do "sh proc cpu history"

and for uplink, please do "sh int" and check for out put drops and if you have a performance monitoring platform check for spikes on overutilistation.

San

New Member

Re: Switch repeatedly loses connection

Thanks Sam,

Maximum CPU% over the last 72 hours is 30% and since that happened within the last 4 hours, it doesnt appear to have been a cpu issue. I have also checked the uplink ports and there are no drops etc.

It all looks fine to me, am I missing something?

switch1#sh int g2/0/24

GigabitEthernet2/0/24 is up, line protocol is up (connected)

Hardware is Gigabit Ethernet, address is 0018.1855.4544 (bia 0018.1855.4544)

MTU 1500 bytes, BW 100000 Kbit, DLY 100 usec,

reliability 255/255, txload 1/255, rxload 1/255

Encapsulation ARPA, loopback not set

Keepalive set (10 sec)

Full-duplex, 100Mb/s, media type is 10/100/1000BaseTX

input flow-control is off, output flow-control is unsupported

ARP type: ARPA, ARP Timeout 04:00:00

Last input 00:00:37, output 00:00:11, output hang never

Last clearing of "show interface" counters never

Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0

Queueing strategy: fifo

Output queue: 0/40 (size/max)

5 minute input rate 0 bits/sec, 0 packets/sec

5 minute output rate 0 bits/sec, 0 packets/sec

4568650 packets input, 496145456 bytes, 0 no buffer

Received 614418 broadcasts (0 multicast)

0 runts, 0 giants, 0 throttles

0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored

0 watchdog, 614417 multicast, 0 pause input

0 input packets with dribble condition detected

4359147 packets output, 542417294 bytes, 0 underruns

0 output errors, 0 collisions, 0 interface resets

0 babbles, 0 late collision, 0 deferred

0 lost carrier, 0 no carrier, 0 PAUSE output

0 output buffer failures, 0 output buffers swapped out

switch1#sh int g1/0/1

GigabitEthernet1/0/1 is up, line protocol is up (connected)

Hardware is Gigabit Ethernet, address is 0018.1855.4542 (bia 0018.1855.4542)

Internet address is 192.168.50.106/30

MTU 1500 bytes, BW 100000 Kbit, DLY 100 usec,

reliability 255/255, txload 1/255, rxload 1/255

Encapsulation ARPA, loopback not set

Keepalive set (10 sec)

Full-duplex, 100Mb/s, media type is 10/100/1000BaseTX

input flow-control is off, output flow-control is unsupported

ARP type: ARPA, ARP Timeout 04:00:00

Last input 00:00:00, output 00:00:01, output hang never

Last clearing of "show interface" counters never

Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0

Queueing strategy: fifo

Output queue: 0/40 (size/max)

5 minute input rate 56000 bits/sec, 3 packets/sec

5 minute output rate 62000 bits/sec, 1 packets/sec

86414711 packets input, 418767872 bytes, 0 no buffer

Received 8576495 broadcasts (7962218 IP multicast)

0 runts, 0 giants, 0 throttles

0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored

0 watchdog, 8576433 multicast, 0 pause input

0 input packets with dribble condition detected

93023508 packets output, 2682384039 bytes, 0 underruns

0 output errors, 0 collisions, 0 interface resets

0 babbles, 0 late collision, 0 deferred

0 lost carrier, 0 no carrier, 0 PAUSE output

0 output buffer failures, 0 output buffers swapped out

Cheers,

Martha.

Re: Switch repeatedly loses connection

It looks ok !

What switch model is it ?

When the issue start, have you done any recent changes ?

Sam

New Member

Re: Switch repeatedly loses connection

It looked okay to me too but I was hoping I had missed something, buggy software...anything.

It is a 3750 and there have been no recent changes, I'm not sure what to check next.

Cheers,

Martha.

Re: Switch repeatedly loses connection

If you can have console access to the switch it would be possible to troubleshoot while issue is taking place. Might not be this particular switch after all, it might for example be a duplicate IP address elsewhere in your LAN, it could be the upstream switch etc..

Please share the issue when you nail it !

Good luck !

Sam

PS: If you are using VRFs I recall seeing a BUG sometimes ago on IOS for 3750

New Member

Re: Switch repeatedly loses connection

Thanks Sam.

The issue is still happening and I am still none the wiser regarding a resolution.

The device is in a remote site so I have no access to it. We are not using VRF's.

I will keep on digging and I will post a fix if I ever get one.

Thanks,

Martha.

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