I might be being special here but...

Magic JohnsonMagic Johnson Member Posts: 414
...please can someone explain this to me before my brain melts, and if this is obvious I deserve a slap, but long day!

I was at a customer site replacing an old managed switch that was put in by another company with a new Cisco SF300.

Now, the router is a Cisco 881, which has 4 L2 switchports and an ethernet WAN port.

From what I saw, there were two links going in to the switch from F0 and F3. I thought this might have been an etherchannel or just STP in action.

Anyway I replaced the 3COM switch with our one and plugged F0 in to one of the gigabit ports on the primary SF300. I checked the router config and the switch and there was nothing special at all, no etherchannels, nada. Anyway I plugged F3 in to the second gigabit port same as on the 3COM and it...just worked. I checked STP, both were forwarding. It's like it was doing load balancing.

Now for all the world I thought that would produce a switching loop, and STP would kick in and block the second link. I checked the frame counters on both ports and they were increasing at about the same rate, load balancing.

What am I missing. icon_sad.gif

p.s I apologise if this is a stupid question in advance.

Comments

  • xnxxnx Member Posts: 464 ■■■□□□□□□□
    Understanding and Configuring the Unidirectional Link Detection Protocol Feature - Cisco

    Possibly UDLD, don't take my word from it I've been on a 1 month break from networking...
    Getting There ...

    Lab Equipment: Using Cisco CSRs and 4 Switches currently
  • Magic JohnsonMagic Johnson Member Posts: 414
    Nope, UDLD not a feature on the switches I put out. icon_sad.gif
  • theodoxatheodoxa Member Posts: 1,340 ■■■■□□□□□□
    Are the 881 Switports in different VLANs or the same VLAN?
    R&S: CCENT CCNA CCNP CCIE [ ]
    Security: CCNA [ ]
    Virtualization: VCA-DCV [ ]
  • Magic JohnsonMagic Johnson Member Posts: 414
    Same VLAN mate, 2.
  • martell1000martell1000 Member Posts: 389
    strange.

    did you try to reboot the device to see if it isnt just a display glitch ?
    And then, I started a blog ...
  • Magic JohnsonMagic Johnson Member Posts: 414
    No, it was during working hours and had to get the changoever done with minimum downtime, hang on I'll go and get the output from the router.

    EDIT: Both ports were flashing though, suggesting activity.
  • Magic JohnsonMagic Johnson Member Posts: 414
    CUSTOMERROUTER#show interfaces
    FastEthernet0 is up, line protocol is up - Goes in to G0 in the Switch
    Hardware is Fast Ethernet, address is 6073.5cc7.ee4e (bia 6073.5cc7.ee4e)
    Description: LAN
    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
    ARP type: ARPA, ARP Timeout 04:00:00
    Last input 00:00:26, output never, 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)
    1 minute input rate 14000 bits/sec, 6 packets/sec
    1 minute output rate 8000 bits/sec, 4 packets/sec
    51027378 packets input, 997394571 bytes, 0 no buffer
    Received 3195024 broadcasts (2065449 multicasts)
    0 runts, 0 giants, 0 throttles
    0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
    0 watchdog, 0 multicast, 0 pause input
    0 input packets with dribble condition detected
    59271824 packets output, 1512771606 bytes, 0 underruns
    0 output errors, 0 collisions, 2 interface resets
    5776 unknown protocol drops
    0 babbles, 0 late collision, 0 deferred
    3 lost carrier, 0 no carrier, 0 pause output
    0 output buffer failures, 0 output buffers swapped out


    REMOVED


    FastEthernet3 is up, line protocol is up - Goes in to G1 on the same Switch
    Hardware is Fast Ethernet, address is 6073.5cc7.ee51 (bia 6073.5cc7.ee51)
    Description: LAN
    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
    ARP type: ARPA, ARP Timeout 04:00:00
    Last input 00:00:27, output never, 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)
    1 minute input rate 0 bits/sec, 0 packets/sec
    1 minute output rate 1000 bits/sec, 2 packets/sec
    7064973 packets input, 763216367 bytes, 0 no buffer
    Received 3130672 broadcasts (3876096 multicasts)
    0 runts, 0 giants, 0 throttles
    0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
    0 watchdog, 0 multicast, 0 pause input
    0 input packets with dribble condition detected
    428488 packets output, 111373020 bytes, 0 underruns
    0 output errors, 0 collisions, 2 interface resets
    5694 unknown protocol drops
    0 babbles, 0 late collision, 0 deferred
    1 lost carrier, 0 no carrier, 0 pause output
    0 output buffer failures, 0 output buffers swapped out


    REMOVED


    Loopback1 is up, line protocol is up
    Hardware is Loopback
    Internet address is X
    MTU 1514 bytes, BW 8000000 Kbit/sec, DLY 5000 usec,
    reliability 255/255, txload 1/255, rxload 1/255
    Encapsulation LOOPBACK, loopback not set
    Keepalive set (10 sec)
    Last input never, output never, 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: 0/0 (size/max)
    5 minute input rate 0 bits/sec, 0 packets/sec
    5 minute output rate 0 bits/sec, 0 packets/sec
    0 packets input, 0 bytes, 0 no buffer
    Received 0 broadcasts (0 IP multicasts)
    0 runts, 0 giants, 0 throttles
    0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort
    0 packets output, 0 bytes, 0 underruns
    0 output errors, 0 collisions, 0 interface resets
    0 unknown protocol drops
    0 output buffer failures, 0 output buffers swapped out

    NVI0 is up, line protocol is up
    Hardware is NVI
    Interface is unnumbered. Using address of FastEthernet4 (wan ip)
    MTU 1514 bytes, BW 56 Kbit/sec, DLY 5000 usec,
    reliability 255/255, txload 1/255, rxload 1/255
    Encapsulation UNKNOWN, loopback not set
    Keepalive set (10 sec)
    Last input never, output never, output hang never
    Last clearing of "show interface" counters never
    Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0
    5 minute input rate 0 bits/sec, 0 packets/sec
    5 minute output rate 0 bits/sec, 0 packets/sec
    0 packets input, 0 bytes, 0 no buffer
    Received 0 broadcasts (0 IP multicasts)
    0 runts, 0 giants, 0 throttles
    0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort
    0 packets output, 0 bytes, 0 underruns
    0 output errors, 0 collisions, 0 interface resets
    0 unknown protocol drops
    0 output buffer failures, 0 output buffers swapped out

    Vlan1 is up, line protocol is up
    Hardware is EtherSVI, address is 6073.5cc7.ee4e (bia 6073.5cc7.ee4e)
    Description: MANAGEMENT VLAN
    Internet address is 10.10.1.1/29
    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 not supported
    ARP type: ARPA, ARP Timeout 04:00:00
    Last input never, output never, 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
    0 packets input, 0 bytes, 0 no buffer
    Received 0 broadcasts (0 IP multicasts)
    0 runts, 0 giants, 0 throttles
    0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
    34 packets output, 2040 bytes, 0 underruns
    0 output errors, 3 interface resets
    0 unknown protocol drops
    0 output buffer failures, 0 output buffers swapped out

    Vlan2 is up, line protocol is up
    Hardware is EtherSVI, address is 6073.5cc7.ee4e (bia 6073.5cc7.ee4e)
    Description: VLAN2
    Internet address is 192.168.1.254/24
    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 not supported
    ARP type: ARPA, ARP Timeout 04:00:00
    Last input 00:00:01, output never, output hang never
    Last clearing of "show interface" counters never
    Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 3
    Queueing strategy: fifo
    Output queue: 0/40 (size/max)
    5 minute input rate 8000 bits/sec, 5 packets/sec
    5 minute output rate 9000 bits/sec, 2 packets/sec
    50938802 packets input, 791369999 bytes, 0 no buffer
    Received 3200253 broadcasts (14381 IP multicasts)
    0 runts, 0 giants, 80 throttles
    0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
    57255644 packets output, 1163885923 bytes, 0 underruns
    0 output errors, 1 interface resets
    511159 unknown protocol drops
    0 output buffer failures, 0 output buffers swapped out


    CUSTOMERROUTER#sh span
    CUSTOMERROUTER#sh spanning-tree


    VLAN2 is executing the ieee compatible Spanning Tree protocol
    Bridge Identifier has priority 32768, address 6073.5cc7.ee4e
    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 4 last change occurred 3d22h ago
    from FastEthernet0
    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


    Port 1 (FastEthernet0) of VLAN2 is forwarding
    Port path cost 19, Port priority 128, Port Identifier 128.1.
    Designated root has priority 32768, address 6073.5cc7.ee4e
    Designated bridge has priority 32768, address 6073.5cc7.ee4e
    Designated port id is 128.1, designated path cost 0
    Timers: message age 0, forward delay 0, hold 0
    Number of transitions to forwarding state: 1
    BPDU: sent 170626, received 2


    Port 4 (FastEthernet3) of VLAN2 is forwarding
    Port path cost 19, Port priority 128, Port Identifier 128.4.
    Designated root has priority 32768, address 6073.5cc7.ee4e
    Designated bridge has priority 32768, address 6073.5cc7.ee4e
    Designated port id is 128.4, designated path cost 0
    Timers: message age 0, forward delay 0, hold 0
    Number of transitions to forwarding state: 1
    BPDU: sent 170562, received 0
  • theodoxatheodoxa Member Posts: 1,340 ■■■■□□□□□□
    Is the SF300 forwarding on both links? The 881 is the STP Root Bridge.
    R&S: CCENT CCNA CCNP CCIE [ ]
    Security: CCNA [ ]
    Virtualization: VCA-DCV [ ]
  • Magic JohnsonMagic Johnson Member Posts: 414
    ARGH I don't know because I can't telnet in to it. Was support that set it up. If it wasn't though surely the frame count for one of the links would be nothing?
  • tomtom1tomtom1 Member Posts: 375
    The root bridge normally has all its ports in FWD mode, so that is normal behaviour. I'm curious to see what the switch reports about spanning-tree operations.
  • Magic JohnsonMagic Johnson Member Posts: 414
    tomtom1 wrote: »
    The root bridge normally has all its ports in FWD mode, so that is normal behaviour. I'm curious to see what the switch reports about spanning-tree operations.

    Is the frame count normal though?

    I can't satisfy your curiosity because it looks like support haven't properly set up the VTY lines on the switch!
  • Dieg0MDieg0M Member Posts: 861
    Packets input/ouput don't mean nothing when you see this: Last clearing of "show interface" counters never, check the 5 min input/output rate instead. Notice that F3: 1 minute input rate 0 bits/sec, 0 packets/sec and that it did not receive any BPDU's: BPDU: sent 170562, received 0
    Follow my CCDE journey at www.routingnull0.com
  • tomtom1tomtom1 Member Posts: 375
    Is the frame count normal though?

    I can't satisfy your curiosity because it looks like support haven't properly set up the VTY lines on the switch!

    Well, the show interface mentions:
    Last clearing of "show interface" counters never

    So what you could do, to get a more realistic view of the counters is do a clear counters <interface name>​ first.
  • Magic JohnsonMagic Johnson Member Posts: 414
    :)

    Once again guys, you've saved my little brain.

    I cleared the counters and F3 is doing nothing basically, it's received 18 packets (?) and is outputting 543 in the last 5 minutes, is this BDPUs it is forwarding on to the blocked port on the SF300?

    Clearly this is STP in action, I missed I think because:

    a) I didn't see the router as being the RB
    b) I couldn't get access to the switch and didn't think about clearing the counters

    Top work guys, repped.
  • xnxxnx Member Posts: 464 ■■■□□□□□□□
    Nice to know it's cleared up now, STP is on by default on Cisco Switches so it'd always have been on unless you turned it off.

    I've also learnt a new command thanks to this thread :P
    Getting There ...

    Lab Equipment: Using Cisco CSRs and 4 Switches currently
  • tomtom1tomtom1 Member Posts: 375
    Hello BPDU's are normally sent out in 802.1d (STP) every 2 seconds by the root bridge, so at least 150 of your packets should be BDPU's. Some other traffic might be sent over that link too, stuff like CDP / VTP advertisements. So it's normal that at least a few packets are traversing the link.

    show spanning-tree root might also come in handy next time. It shows you an overview of STP processes running (2 in my case - PVST with 2 vlans). It shows you the root BID and root ports (if applicable). A root bridge obviously has no root ports.
    Root    Hello Max FwdVlan                   Root ID          Cost    Time  Age Dly  Root Port
    ---------------- -------------------- --------- ----- --- ---  ------------
    VLAN0001         32768 000e.58e4.c98e    200019    2    6   4  Fa0/1           
    VLAN0002         32768 000e.58e4.c98e    200038    2    6   4  Fa0/9           
    
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