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New Member

6509 interface UDLD


I have a 3750 switch connected to a 6509 switch using MM fiber and doing layer 3. Lately i have experienced some serious problems with this link. occassionaly,it used to go down and I needed to shut and unshut either end of the link in order to bring the link up.This used to happen since the interfaces were showing up and up at both end and yet were not reachable. i enabled udld on both interfaces yesterday and now when it goes down, the inetrface is errdisable due to udld as shown here in the output.

core01#sh int gig4/1

GigabitEthernet4/1 is down, line protocol is down (err-disabled)

Hardware is C6k 1000Mb 802.3, address is 000f.3577.a44a (bia 000f.3577.a44a)

Internet address is 10.5.x.y/24

MTU 1500 bytes, BW 1000000 Kbit, 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 SX

input flow-control is off, output flow-control is off

Clock mode is auto

ARP type: ARPA, ARP Timeout 04:00:00

Last input 11:34:20, output 11:34:17, output hang never

Last clearing of "show interface" counters 1d23h

Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0

core01#sh int gig4/1 status

Port Name Status Vlan Duplex Speed Type

Gi4/1 err-disabled 1 full 1000 1000BaseSX


core01#sh logg

Oct 3 19:10:36.125: %OSPF-5-ADJCHG: Process 222, Nbr on GigabitEth

ernet4/1 from INIT to DOWN, Neighbor Down: Interface down or detached

Oct 3 19:10:36.073: %UDLD-SP-4-UDLD_PORT_DISABLED: UDLD disabled interface Gi4/

1, unidirectional link detected

Oct 3 19:10:36.073: %PM-SP-4-ERR_DISABLE: udld error detected on Gi4/1, putting

Gi4/1 in err-disable state


Any idea what could be happening and how do I resolve this?

New Member

Re: 6509 interface UDLD


I think you should check your fiber. It seems the UDLD proces detected a unidirectional link so it seems one of the fibers is failing

bjw Silver

Re: 6509 interface UDLD

I would do a couple of things:

1. Test the fiber link with a good 1000BaseX tester

2. Configure the trunk links for ON ON

3. Try UDLD aggressive mode if not already done.

4. Change the GBICs/SFPs on both ends of the link and RMA the old ones to TAC if replacements work fine.

New Member

Re: 6509 interface UDLD

Thanks folks but since the interfaces are routed,how do I turn the trunk ON ON ?

bjw Silver

Re: 6509 interface UDLD

If they are not trunks, then you can omit that recommendation.