switch goes offline for 30secs when i reboot a different switch

[dborg]

Hi All

I have noticed when i reboot one of my switches the following sequence occurs

a)reboot switch 1

b)switch 1 does its reboot (takes 58sec approx)

c)just before switch one comes back online switch 2 goes offline (2sec approx)

d)switch 1 is online

e)switch 2 comes online after 30 seconds

Can anyone think of what could be wrong and cause the above to occur ?  Its really strange because to two switches plug into a backbone switch and are not piggy backed to each other...Even more bizarre is it goes offline just before the other switch comes back online

Any ideas would be good as i don't like the idea of the other switch going offline when i need to reboot a different switch...

Cheers

Dom

[Collin Clark]

I would guess it's spanning tree. Can you console in to the second switch or turn up logging to get more info?

[Giuseppe Larosa]

Hello Dom,

spanning tree protocol may be behind what you see:

a change in topology (both events switch1 goes offline, switch1 comes on line qualify as topology changes) causes STP to recalculate.

if you are using 802.1D spanning-tree including Cisco PVST+ going via the listening and learning states takes 15 seconds each.

Convergence is much faster with 802.1W  Rapid STP or with Cisco Rapid PVST or with 802.1s MST because it uses handshake mechanisms and doesn't need to move from blocking to listening for 15 seconds and then from listening to learning for other 15 seconds.

so I would check with show spanning-tree summary what type of STP you are running on all involved switches.

then you can use show spanning-tree detail to verify for the vlan where the management IP of switch2 is connected to if there have been recent topology changes.

Hope to help

Giuseppe

[dborg]

Hi Guiseppe And Colin

appreciate your comments

i cant telnet to my first switch at the moment to get stp info but here is switch 2 details(mgmt port is vlan1):

switch 2 is a catalyst 2950 and the other switch is a catalyst express 500g

switch05#show spanning-tree

VLAN0001
  Spanning tree enabled protocol ieee
  Root ID    Priority    32768
             Address     0012.79cb.9060
             Cost        20019
             Port        24 (FastEthernet0/24)
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec

  Bridge ID  Priority    32769  (priority 32768 sys-id-ext 1)
             Address     000b.bed6.bd40
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec
             Aging Time 300

Interface        Role Sts Cost      Prio.Nbr Type
---------------- ---- --- --------- -------- --------------------------------
Fa0/11           Desg FWD 19        128.11   P2p
Fa0/12           Desg FWD 100       128.12   P2p
Fa0/14           Desg FWD 19        128.14   P2p
Fa0/15           Desg FWD 19        128.15   P2p
Fa0/16           Desg FWD 19        128.16   P2p
Fa0/18           Desg FWD 19        128.18   P2p
Fa0/24           Root FWD 19        128.24   P2p

-Detail-
switch05#show spanning-tree detail

VLAN0001 is executing the ieee compatible Spanning Tree protocol
  Bridge Identifier has priority 32768, sysid 1, address 000b.bed6.bd40
  Configured hello time 2, max age 20, forward delay 15
  Current root has priority 32768, address 0012.79cb.9060
  Root port is 24 (FastEthernet0/24), cost of root path is 20019
  Topology change flag not set, detected flag not set
  Number of topology changes 127 last change occurred 00:03:21 ago
          from FastEthernet0/24
  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

Port 11 (FastEthernet0/11) of VLAN0001 is forwarding
   Port path cost 19, Port priority 128, Port Identifier 128.11.
   Designated root has priority 32768, address 0012.79cb.9060
   Designated bridge has priority 32769, address 000b.bed6.bd40
   Designated port id is 128.11, designated path cost 20019
   Timers: message age 0, forward delay 0, hold 0
   Number of transitions to forwarding state: 1
   Link type is point-to-point by default
   BPDU: sent 41442, received 0

Port 12 (FastEthernet0/12) of VLAN0001 is forwarding
   Port path cost 100, Port priority 128, Port Identifier 128.12.
   Designated root has priority 32768, address 0012.79cb.9060
   Designated bridge has priority 32769, address 000b.bed6.bd40
   Designated port id is 128.12, designated path cost 20019
   Timers: message age 0, forward delay 0, hold 0
   Number of transitions to forwarding state: 1
   Link type is point-to-point by default
   BPDU: sent 10911, received 0

Port 14 (FastEthernet0/14) of VLAN0001 is forwarding
   Port path cost 19, Port priority 128, Port Identifier 128.14.
   Designated root has priority 32768, address 0012.79cb.9060
   Designated bridge has priority 32769, address 000b.bed6.bd40
   Designated port id is 128.14, designated path cost 20019
   Timers: message age 0, forward delay 0, hold 0
   Number of transitions to forwarding state: 1
   Link type is point-to-point by default
   BPDU: sent 58594, received 0

Port 15 (FastEthernet0/15) of VLAN0001 is forwarding
   Port path cost 19, Port priority 128, Port Identifier 128.15.
   Designated root has priority 32768, address 0012.79cb.9060
   Designated bridge has priority 32769, address 000b.bed6.bd40
   Designated port id is 128.15, designated path cost 20019
   Timers: message age 0, forward delay 0, hold 0
   Number of transitions to forwarding state: 1
   Link type is point-to-point by default
   BPDU: sent 28694, received 0

Port 16 (FastEthernet0/16) of VLAN0001 is forwarding
   Port path cost 19, Port priority 128, Port Identifier 128.16.
   Designated root has priority 32768, address 0012.79cb.9060
   Designated bridge has priority 32769, address 000b.bed6.bd40
   Designated port id is 128.16, designated path cost 20019
   Timers: message age 0, forward delay 0, hold 0
   Number of transitions to forwarding state: 1
   Link type is point-to-point by default
   BPDU: sent 58590, received 0

Port 18 (FastEthernet0/18) of VLAN0001 is forwarding
   Port path cost 19, Port priority 128, Port Identifier 128.18.
   Designated root has priority 32768, address 0012.79cb.9060
   Designated bridge has priority 32769, address 000b.bed6.bd40
   Designated port id is 128.18, designated path cost 20019
   Timers: message age 0, forward delay 0, hold 0
   Number of transitions to forwarding state: 1
   Link type is point-to-point by default
   BPDU: sent 58589, received 0

Port 24 (FastEthernet0/24) of VLAN0001 is forwarding
   Port path cost 19, Port priority 128, Port Identifier 128.24.
   Designated root has priority 32768, address 0012.79cb.9060
   Designated bridge has priority 32768, address 0025.6194.8ec0
   Designated port id is 128.43, designated path cost 20000
   Timers: message age 2, forward delay 0, hold 0
   Number of transitions to forwarding state: 22
   Link type is point-to-point by default
   BPDU: sent 142, received 58569

So basically if there is a mismatch of stp between the two devices should i turn stp off  to avoid going offline for a brief period ?

thanks heaps for your help

Dom

[mukul-joshi]

Hi

I think the best way to solve the problem is to configure RSTP becuase in that that case downtime is 5 sec or so.

BRegards

Mukul

[Giuseppe Larosa]

Hello Dom,

>> Number of topology changes 127 last change occurred 00:03:21 ago

you ahould look at this line after each test, you should see the number of changes that increments and the last change time close to the SW1 offline/inline events.

As noted by other colleague moving to Rapid PVST could reduce the offline time of SW2 during SW1 power cycle

>> So basically if there is a mismatch of stp between the two devices should i turn stp off  to avoid going offline for a brief period ?

No, I strongly recommend to keep using STP as it is there to avoid bridging loops. The  question may be of tuning or moving to Rapid PVST but do not disable it for your own safety!

>> switch 2 is a catalyst 2950 and the other switch is a catalyst express 500g

This may make moving to rapid STP difficult the C2950 may have an old image and the 500g is not a real Cisco class switch.

Hope to help

Giuseppe