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Broadcast address FF-FF-FF-FF-FF-FF

hostettle
Beginner
Beginner

Hello,

Sorry for my ignorance.

(1) I can understand this line in the command table :

All    0180.c200.0000    STATIC      CPU

Whatever the VLAN number, all MAC frames carrying a BPDU do not enter the forwarding datase, they are blocked in this direction.

(2) I don't know why there is this line !

All    ffff.ffff.ffff    STATIC      CPU

Normally, the broadcast address is permitted to enter the forwarding database.

Did I miss something?

Best regards,

Michel

.

2 Accepted Solutions

Accepted Solutions

paolo bevilacqua
Hall of Fame
Hall of Fame

CPU needs to see broadcasts, for various reasons.

View solution in original post

rsimoni
Cisco Employee
Cisco Employee

they are not blocked at all; those lines mean that frames destined to those MAC addresses are sent to the CPU to be processed there. Only the control plane is able to process BPDU's or other control plane protocols (i.e. ARP request sent to broadcast address need to be seen and processed by the CPU).

View solution in original post

3 Replies 3

paolo bevilacqua
Hall of Fame
Hall of Fame

CPU needs to see broadcasts, for various reasons.

rsimoni
Cisco Employee
Cisco Employee

they are not blocked at all; those lines mean that frames destined to those MAC addresses are sent to the CPU to be processed there. Only the control plane is able to process BPDU's or other control plane protocols (i.e. ARP request sent to broadcast address need to be seen and processed by the CPU).

Hello Paolo and Riccardo,

I confused the filtering process described by IUT-T and by IEEE.

I agree, these 2 lines say that MAC frames with these DA address are sent to the CPU, that is the direction of the sublayers client of the MAC sublayer (according to the L/T field).

These lines don't say that :

- Frames wih DA = 01- 80-C2-00-00-00 are not forwarded (relayed to another port)

- Frames with DA = FF-FF-FF-FF-FF-FF are forwarded

It's different for ITU-T (G.8021). The filtering process block or pass the frames in the switching matrix. So, we don't have something similar to the second line.

Best regards,

Michel

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