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Community Member

Late Collision Interface down

Hi all,

On my router I have this log:

Jan 27 10:24:19.116: %GT96K_FE-5-LATECOLL: Late Collision on int FastEthernet0/0

Jan 27 10:24:21.116: %LINK-3-UPDOWN: Interface FastEthernet0/0, changed state to up

Jan 27 10:33:28.052: %GT96K_FE-5-LATECOLL: Late Collision on int FastEthernet0/0

Jan 27 10:33:30.052: %LINK-3-UPDOWN: Interface FastEthernet0/0, changed state to up

Jan 27 11:15:21.831: %GT96K_FE-5-LATECOLL: Late Collision on int FastEthernet0/0

Jan 27 11:15:23.835: %LINK-3-UPDOWN: Interface FastEthernet0/0, changed state to up

Is it a normal behaviour that when the router detects a late-collison, the interface fastethernet goes down?

Thanks in advance

Gianluca

7 REPLIES

Re: Late Collision Interface down

Hi Gianluca

The below mentioned are the possible causes for the late collisions..

1.incorrect cabling or a non-compliant number of hubs in the network.

2.Bad network interface cards (NICs) can also cause late collisions.

regds

Community Member

Re: Late Collision Interface down

A late collision occurs when two devices transmit at the same time, but due to cabling errors (most commonly, excessive network segment length or repeaters between devices) neither detects a collision. The reason this happens is because the time to propagate the signal from one end of the network to another is longer than the time to put the entire packet on the network, so the two devices that cause the late collision never see that the other?s sending until after it puts the entire packet on the network. The transmitter after the first "slot time" of 64 byte times detects late collisions. They are only detected during transmissions of packets longer than 64 bytes. Its detection is exactly the same as for a normal collision; it just happens "too late." Typical causes of late collisions are segment cable lengths in excess of the maximum permitted for the cable type, faulty connectors or improper cabling, excessive numbers of repeaters between network devices, and defective Ethernet transceivers or controllers. Another bad thing about late collisions is that they occur for small packets also, but cannot be detected by the transmitter. A network suffering a measurable rate of late collisions (on large packets) is also suffering lost small packets. The higher protocols do not cope well with such losses. Well, they cope, but at much reduced speed. A 1% packet loss is enough to reduce the speed of NFS by 90% with the default retransmission timers. That?s a 10X amplification of the problem. Finally, Ethernet controllers do not retransmit packets lost to late collisions

Community Member

Re: Late Collision Interface down

Thanks a lot for your answer...but it is normal the the interface fastethernet goes down?

Regards

Gianluca

Re: Late Collision Interface down

Hi Gianluca

In normal working conditions you don't get your fastethernet down.

You need to troubleshoot as mentioned in the link or in the previous post and make the link stable..

regds

Re: Late Collision Interface down

Hi,

I would first check the cabling, which could cause both, interface up/down and late collisions.

Might be that the ethernet keepalives are "destroyed" and as such the int goes down.

Regards, Martin

Community Member

Re: Late Collision Interface down

Ok Thanks a lot everybody..

I'm coming to check...

Gianluca

Community Member

I had a same problem too.

I had a same problem too.

We replaced the cable, no help.

We replaced the router port, no help

we rebooted the device, no help.

We rebooted transport box, no help.

lastly, as the interface speed and duplex was auto and auto on router and vendor has hard coded it to 100 & full.

We hard coded too to the same settings.

It worked, Late collisions have stopped.

Thanks.

Nagasheshu.

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