Catalyst sending 60-Bytes frame to itself (ethertype 0x9000)

[HUBERT RESCH]

Hi,

observed in our Catalyst-based network that the switches are sometimes sending "Loopback"-Packets

(Ethertype 0x9000) to its own MAC-Address. 46-Bytes Data contain only zeros.

Does anybody know what the switch is doing with this frame ?????

Kind Regards

Hubert

[lgijssel]

Hubert,

These packets are used, as you say, for loopback purposes. The switch, and most other cisco devices use these packets to check wheter the LAN interface is operational (up) or not.

Regards,

Leo

[HUBERT RESCH]

Hi Leo,

how will the switch dedect if the interface is up by sending such a packet out for example through a port

where a workstation is connected. The Workstation will not send back the loop-frame, true ??

Kind Regards

Hubert

[lgijssel]

Herbert,

It simply listens to its own transmissions.

When it receives a datagram with its own mac adress it knows the TX and RX leads on the LAN are both operational.

Leo