Link Status on switch down down

Unanswered Question
Jan 16th, 2008

server team is trying to turn up a new server on our network-however the port they are conncected to is showing DOWN DOWN

GigabitEthernet1/0/21 is down, line protocol is down (notconnect)

Hardware is Gigabit Ethernet, address is 0019.5638.f995 (bia 0019.5638.f995

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)

Full-duplex, 100Mb/s, media type is 10/100/1000BaseTX

this can only be a physical layer problem correct?

even if they have bad gatweay configuration..there should still be a status change

we also have another device connected that is up up .....but not in the MAC table

  • 1
  • 2
  • 3
  • 4
  • 5
Overall Rating: 0 (0 ratings)
plumbis000 Wed, 01/16/2008 - 09:06

down/down almost always is a layer 1 issue, either the port, the cable. I'd test both of these on working interfaces to rule out other possibilities.

If you have a configuration problem you'd have up/up or up/down but just wouldn't be able to get traffic to go anywhere.

Depending on what the up/up device is, it might be lying. GSRs do this sometimes.

ankbhasi Wed, 01/16/2008 - 09:07

Hi Friend,

This is surely a physical layer issue. Either a bad cable most likely or some nic card issue on server.

Can you confirm what speed and duplex settings is been done on a switchport on which this server is connected? Also which switch model is this?



nygenxny123 Wed, 01/16/2008 - 09:12

hello this is a 3750 switch..

also ..what about the port showing up up

but the mac-address-table not populating?

ankbhasi Wed, 01/16/2008 - 09:17

Hi Friend,

Can you just set the speed and duplex settings as auto on switch port as well as on server side and see if that resolves the issue.



justin.wade Wed, 01/16/2008 - 09:13

Looks like the speed and duplex are hard set on this interface. Your speed is 100Mb if the speed of the servers NIC is hard set to 10Mb or 1000Mb the interface will not come up. The speed if hard set must match the hard set speed of the device on the other end. However, if you have one side hard set and the other is left to autonegotiate the device set to autonegotiate will select the same speed as the device that is hard set, provide that the device set to autonegotiate supports the same speed. However, if both are hard set to different speeds the link will not come up, I hope this makes sense.

As far as not seeing the MAC address of the other device in your MAC table goes, have you tried generating any traffic on the PC? The MAC table has an age time of 300 sec (5 Min) by default, perhaps the PC has not sent out any frames for the last 5 minutes.

Also a misconfigured default gateway would not effect either of these issues. This looks like a layer 1 issue to me. I would also recheck and test my cabling.

Hope this helps.


This Discussion