Rapid-pvst wiith pvst

amiie00 · July 24, 2021, 11:03am

Dear admin,

I found issue interface up/down on core switch every time when I plug interface on access switch.
Core switch was configured spanning tree mode pvst and Access switch with rapid-pvst.
I’m not sure STP with 2 mode can combine and I don’t found loop in 2 switch.
Cloud tell me, STP 2 mode it’s cause of interface up/down or not?

lagapidis · July 26, 2021, 6:32am

Hello Nattiya

PVST and Rapid PVST are compatible with each other. In such cases Rapid PVST falls back to operating like PVST, so you should have no issues with the interoperability of these two STP protocols. This Cisco document further describes this interoperability:

When you say “I found issue interface up/down” what do you mean? Are you seeing an L2 loop? Is the interface flapping? Do you see errors on the interfaces? Let us know more so that we can help you further in troubleshooting.

I hope this has been helpful!

Laz

amiie00 · July 27, 2021, 2:32am

Dear Lagapides

Thank you for you replied, I have noticed Interface which connect to distribute switch is up/down every time that STP topology changes (And it is up/down only on Core switch interface Only, Distribute has no log interface up/down but found STP topology changes from interface which connect to access switch)

On Core switch shown:
show interface (which up/down state) on Core switch :

Core-Switch#sh int g1/0/14
GigabitEthernet1/0/14 is up, line protocol is down (notconnect) *----> and then line protocol is up*
  Hardware is Gigabit Ethernet, address is 4ce1.7555.448e (bia 4ce1.7555.448e)
  Description: to ASW-2950-FAC-1-temp
  MTU 1500 bytes, BW 100000 Kbit/sec, 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 on, output flow-control is unsupported
  ARP type: ARPA, ARP Timeout 04:00:00
  Last input 00:00:21, output 00:00:00, output hang never
  Last clearing of "show interface" counters 2d10h
  Input queue: 0/2000/0/0 (size/max/drops/flushes); Total output drops: 5461
  Queueing strategy: fifo
  Output queue: 0/40 (size/max)
  5 minute input rate 218000 bits/sec, 107 packets/sec
  5 minute output rate 460000 bits/sec, 90 packets/sec
     15172136 packets input, 4344071086 bytes, 0 no buffer
     Received 1334815 broadcasts (416646 multicasts)
     0 runts, 0 giants, 0 throttles
     39 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
     0 watchdog, 416646 multicast, 0 pause input
     0 input packets with dribble condition detected
     14838084 packets output, 8364169398 bytes, 0 underruns
     0 output errors, 0 collisions, 0 interface resets
     0 unknown protocol drops
     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

Show log on Core switch :

Jul 27 09:03:30.393 GMT: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet1/0/14, changed state to down
Jul 27 09:03:35.176 GMT: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet1/0/14, changed state to up
Jul 27 09:10:17.726 GMT: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet1/0/14, changed state to down
Jul 27 09:10:22.461 GMT: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet1/0/14, changed state to up
Jul 27 09:11:17.178 GMT: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet1/0/14, changed state to down
Jul 27 09:11:21.926 GMT: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet1/0/14, changed state to up
Jul 27 09:13:08.282 GMT: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet1/0/14, changed state to down
Jul 27 09:13:12.971 GMT: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet1/0/14, changed state to up
Jul 27 09:13:46.200 GMT: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet1/0/14, changed state to down
Jul 27 09:13:50.938 GMT: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet1/0/14, changed state to up
Jul 27 09:14:29.097 GMT: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet1/0/14, changed state to down
Jul 27 09:14:33.879 GMT: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet1/0/14, changed state to up
Jul 27 09:16:13.027 GMT: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet1/0/14, changed state to down
Jul 27 09:16:17.769 GMT: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet1/0/14, changed state to up
Jul 27 09:17:28.441 GMT: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet1/0/14, changed state to down
Jul 27 09:17:33.139 GMT: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet1/0/14, changed state to up

And how spanning tree on Core switch :

Core-Switch#sh spanning-tree vlan 223 de

 VLAN0223 is executing the ieee compatible Spanning Tree protocol
  Bridge Identifier has priority 24576, sysid 223, address 4ce1.7555.4480
  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 1853 last change occurred 00:01:24 ago
          from GigabitEthernet1/0/14
  Times:  hold 1, topology change 35, notification 2
          hello 2, max age 20, forward delay 15
  Timers: hello 1, topology change 0, notification 0, aging 300

On Access switch has no log up/down on any interface and found STP topology changes on interface which connect to Distribute switch.

Core switch and Distribute switch : PVST
Config on core switch :

spanning-tree mode pvst
spanning-tree extend system-id
spanning-tree vlan 1-2,203-206,222-223,230-231 priority 24576

Config on distribute switch :
spanning-tree mode pvst
spanning-tree extend system-id

**Access switch : Rapid-pvst**
spanning-tree mode rapid-pvst
spanning-tree extend system-id

Thank you.

lagapidis · July 28, 2021, 5:19am

Hello Nattiya

Thank you for the extra information, this is helpful. So there are a couple of things we see here. First of all, the interface is indeed flapping. Flapping is the term we use to describe this behaviour of going up and down. However, we see the following:

The flapping is taking place only on the line protocol, We don’t see any link flapping. Link flapping would be indicated with an additional syslog messages of the type LINK-3-UPDOWN.
The flapping seems to bring down the interface for four or five seconds, but the next time it goes down may be after six or seven minutes, or after less than a minute.

Now because the timing is not at regular intervals, I don’t believe that the problem is with STP. Every time an interface goes up or down, the STP topology changes as a result, but it is not the cause of the problem, at least I don’t believe so in this case.

In the show interface output there are over 5000 output drops as well as 39 input errors. This alone does not tell us about the flapping, but it may be related.

To further troubleshoot this, try to take a look at the output to the following commands:

show int gi1/0/4 counters
show int gi1/0/4 counters errors
show int gi1/0/4 counters protocol status
show int gi1/0/4 stats
show int gi1/0/4 status

The results may give us some more insight. If you would like, feel free to share this with us here so we can help the troubleshooting process further.

I hope this has been helpful!

Laz