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New Member

Port is down between two 3550s

I am trying to setup trunk between two 3550s. I configured the trunk one each switch as usual but the port always show interface is down and notconnected (The cable is good).

The IOS version is 12.1(22)EA1a.

interface FastEthernet0/24
switchport trunk encapsulation dot1q
switchport mode trunk

Switch#sh int f0/24   
FastEthernet0/24 is down, line protocol is down (notconnect)
  Hardware is Fast Ethernet, address is 000e.84f6.3618 (bia 000e.84f6.3618)
  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)
  Auto-duplex, Auto-speed, media type is 100BaseTX
  input flow-control is off, output flow-control is unsupported
  ARP type: ARPA, ARP Timeout 04:00:00
  Last input never, output 00:10:55, 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

I was thinking on trunk encapsulation and tried both dot1q and isl were all not working. I even removed the trunk setting and put them on same VLAN, the ports still show down and notconnected. This is weird to me. When I connected any one of 3550 with other device like ASA5520 with trunk setting, it works fine.

Is there special setting for configuring trunk between 3550s?

Thank you in advance.

New Member

Re: Port is down between two 3550s

Here is a stupid question but is sometimes overlooked, are you using a crossover cable?

New Member

Re: Port is down between two 3550s

Of cause not crossed cable as I mentioned the cable is correct otherwise I won't ask this stupid question

Hall of Fame Super Bronze

Re: Port is down between two 3550s

Switch <-> Switch you need a Xover cable unless the switches have Auto-MDIX support (which I don't recall being supported on


Switch <-> ASA a regular cable will work.

Do yourself a favor and get a Xover cable.



New Member

Re: Port is down between two 3550s

OMG, never pay attention on that. Auto-adapt has been implemented to most of ethernet cards in last decade.

Anyway, let me try cross cable thgouh. Thanks a lot.