So this is a first for me. I have been digging into some communication issues between my client whose router keeps losing its connection to the our gateway.
Setup is as follows: Mikrotik RB (Gateway) <-> Cisco 3560 w PoE <-> A5c <-> C5x <-> Mikrotik RB (Customer)
Mikrotik port is under a bridge interface to take advantage of rstp. MTU 1500
switchport trunk encapsulation dot1q
switchport mode trunk
MTU is 1500 on Cisco
When I run a show int gi0/24 i get:
show int gi0/24
GigabitEthernet0/24 is up, line protocol is up (connected)
Hardware is Gigabit Ethernet, address is a80c.0d9e.2398 (bia a80c.0d9e.2398)
MTU 1500 bytes, BW 1000000 Kbit/sec, DLY 10 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation ARPA, loopback not set
Keepalive set (10 sec)
Full-duplex, 1000Mb/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 00:00:11, output 00:00:00, 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 463000 bits/sec, 115 packets/sec
5 minute output rate 5952000 bits/sec, 559 packets/sec
901755292 packets input, 739437279860 bytes, 0 no buffer
Received 747724 broadcasts (277675 multicasts)
0 runts, 0 giants, 0 throttles
0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
0 watchdog, 277675 multicast, 0 pause input
0 input packets with dribble condition detected
1472633156 packets output, 1056581705260 bytes, 0 underruns
0 output errors, 0 collisions, 1 interface resets
11008 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
Upon researching, I see where the DTP tunking protocol can cause this, but this is my first time seeing this as we have multiple other A5c’s out there without this issue.
Has anyone else run across this error? I believe the switchport nonegotiate command will disable dtp and fix, but my nerdy packet analysis minded brain wants to investigate the root cause a little more.
@William5 I know you have a similar setup, ever see this on your Cisco’s before?
I have noticed that on a few of my other APs I have enabled the 2474 MTU, wonder if that would help?