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CAM Table when it gets full and broadcast leakage

((When the CAM table is full, all excess unicast frames are treated as broadcast frames.

When this occurs it is possible for traffic to leak between VLANs )).

The first paragraph is ok for me,,,but the second one, I get confused,, my confusion is this: if there is broadcast within a specific VLAN (in case if CAM is not full),,we do not put in our consideration might be there is a broadcast leakage ,,,,Don't we? Why do we consider that (a broadcast leakage) when the CAM table is full ?

3 REPLIES

Re: CAM Table when it gets full and broadcast leakage

The association of a frame with a particular vlan is learned via the CAM table (or mac-address table). When a node transmits a frame, the switch will be able to determine it's originating port and this is called learning. So, learning is done via the source-adresses which are mostly unicast. This is the key to your question.

If the table is not filled, the originating port (and hence it's associated vlan-id) are always learned, no problem here. If the table is overflowing, the switch is unable to determine (or remember) from which vlan the packet originated which opens the possibility of transmitting it with an incorrect vlan-id.

Broadcast adresses (all 1's) are not in the table and you will never see a frame with "broadcast" as the source address.

Regards,

Leo

New Member

Re: CAM Table when it gets full and broadcast leakage

((When a node transmits a frame, the switch will be able to determine it's originating port and this is called learning))

1- You meant here the first step of How LAN switch works(1/5 which are 1-learning, 2- floodind, 3-forwarding, 4- filtering, 5- Aging),,,did not you ?

2- You meant by "originating port" ,,,receiving port for the packet form the source,, as this port is recorded into Lookup table (CAM),,,,,did not you ?

((If the table is overflowing, the switch is unable to determine (or remember) from which vlan the packet originated which opens the possibility of transmitting it with an incorrect vlan-id)).

Here I did not get you ,,,do you means that a packet might not have a record in a CAM table ?

New Member

Re: CAM Table when it gets full and broadcast leakage

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