loop protocol

[lcaruso]

Hi,

I have a 3650 running recent code and I'm noticing these packets when running Wireshark on my directly connected desktop. What are these packets for and how do I turn this feature off if it simply the switch pinging itself at a layer 2 default loopback interface? Thanks.

[Richard Burts · Accepted solution]

What you are seeing there are the Ethernet keepalive messages. In earlier implementations of Ethernet it was more important that the interface validate operation of the network by sending a frame where the source MAC and destination MAC were the MAC of the interface.

If the interface accepts it the command no keepalive will stop them.

HTH

Rick

Sent from Cisco Technical Support iPhone App

[Peter Paluch · Accepted solution]

Hello,

In addition to Rick's explanation, Cisco Catalyst switches are using the LOOP protocol to detect self-looped ports, i.e. ports that keep receiving the same traffic they sent themselves - because of some unfortunate loop in the network. If a switchport receives a LOOP frame it sent itself, it will be put into errdisabled state.

There was a rather lengthy discussion primarily between me and Giuseppe about this topic with Giuseppe pointing out different important aspects of the LOOP protocol. You may be interested in reading it here:

https://supportforums.cisco.com/message/3005684#3005684

Best regards,

Peter

[jaherullah]

I also have same loop protocol message captured, The link is not opening. can you please paste what to be done to fix this ?

[paheeradan.nagulan]

Hi @Peter Paluch ,

I'm interested in reading that link. Looks like the link is expired. Do you happen to have the updated link? Thanks

[Peter Paluch]

Hello,

Check the following two links. They are part of the same thread.

https://community.cisco.com/t5/switching/what-s-a-loop-traffic-in-ethereal/m-p/1407051/highlight/true#M131972

https://community.cisco.com/t5/switching/what-s-a-loop-traffic-in-ethereal/m-p/1407043/highlight/true#M131964

Best regards,
Peter

[lcaruso]

Thanks to both of you for the information and that link is a nice, in-depth discussion.

Larry

[Mikheil Zhizhilashvili]

Thanks your current information ! true story 10x 

there is no loop packets anymore