[c-nsp] Strange ethernet frames on switch client ports

[Adrian Pirciu]

These are special Ethernet defined for loopback test: (type 9000 hex).
As you can see, the source and destination macs are the same. This 
special type of packet helps the switch notice if any layer1 loop 
forms, the moment when it receives the packet transmitted on the same 
port (it disables the port when this happens, unless the protection is 
disabled). I don't know if you cand disable this (maybe using 
err-disable loopback something) but it is possible that the packets 
will still be sent. . 

On Friday 19 November 2004 10:52, Piltrafilla wrote:
> Hi people,
>
> I am trying to completely clean up management frames on client ports
> applying best common practices such as BPDU filtering
>
> interface FastEthernetX/Y
>  switchport access vlan NN
>  switchport mode access
>  no ip address
>  no cdp enable
>  spanning-tree portfast
>  spanning-tree bpdufilter enable
>  spanning-tree bpduguard enable
>  spanning-tree guard root
> !
>
> This config removes 802.1d BPDUs, CDP frames, etc but on that port I
> still see this management frames. I can't find which feature I must
> disable in order to avoid them:
>
> 09:39:26.970184 0:f:90:fd:97:85 0:f:90:fd:97:85 9000 60:
>                          0000 0100 0000 0000 0000 0000 0000 0000
>                          0000 0000 0000 0000 0000 0000 0000 0000
>                          0000 0000 0000 0000 0000 0000 0000
> 09:39:36.975274 0:f:90:fd:97:85 0:f:90:fd:97:85 9000 60:
>                          0000 0100 0000 0000 0000 0000 0000 0000
>                          0000 0000 0000 0000 0000 0000 0000 0000
>                          0000 0000 0000 0000 0000 0000 0000
> 09:39:56.975158 0:f:90:fd:97:85 0:f:90:fd:97:85 9000 60:
>                          0000 0100 0000 0000 0000 0000 0000 0000
>                          0000 0000 0000 0000 0000 0000 0000 0000
>                          0000 0000 0000 0000 0000 0000 0000
>
> MAC address belongs to the switch as show mac-address-table says.
>
>    All    000f.90fd.9785    STATIC      CPU
>
> Anyone can give me some light on that? :)
>
> Thank you in advance,
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-- 
------------------------------------------------------------------------
Adrian Pirciu
Network Engineer