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New Member

layer 2 broadcast

Does anybody happen to know if a layer 2 broadcast is being sent over a specific vlan or all vlans? For example, if a broadcast frame comes in on a port that happened to be on vlan20, will the switch flood this broadcast only to the ports that happened to be on the same vlan20?

Thanks.

4 REPLIES
Bronze

Re: layer 2 broadcast

I'm assuming you're talking about a normal 'access' port, not a trunk.

That being the case, a layer 2 broadcast coming into that port is going to be limited to the VLAN that the port is configured to be in - only VLAN 20, in your example.

There are some notable exceptions, so this may not be 100% true in a specific configuration or situation.

Consider ports in a given VLAN to be in their own physical LAN, seperate and distinct from other VLANs.

HTH

John

New Member

Re: layer 2 broadcast

Thanks for your response. So, the switch is aware of what vlan a port belongs to and acts accordingly. For example, if I have a couple of servers, patched into ports on different vlans on a switch with layer 3 and do a "ping" from one server to the other, that switch will be aware of the different vlans and will send it to the layer 3? Thanks again...

New Member

Re: layer 2 broadcast

Short answer - Yes.

Broadcasts in a multi-vlan switch environment are contained within their own vlan. As are multicast frames.

peter

Green

Re: layer 2 broadcast

Cisco's definition for a VLAN (for testing purposes anyway) is that a VLAN is a broadcast domain.

Following that definition, by default, broadcasts (and multicasts) will be limited to the VLAN in which they occur (unless the layer 3 device is otherwise configured to propagate them).

FWIW

Scott

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