Switch configuration

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Sep 4th, 2009
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I have an application that needs the following from 1 port of a switch.

If MAC is learned from the same port the switch should send the frame back from the port that it was received .

How can i force it in cisco switch ?

I know that it is different from a regular switch bahviour



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Joseph W. Doherty Sat, 09/05/2009 - 04:40
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When a switch learns a source MAC on a port it does sent frames to that port with that destination MAC.

Could you clarify what you're trying to accomplish a bit more?

yoram12345 Sat, 09/05/2009 - 10:20
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Hi josephdoherty ,

I will try :

The switch gets the ethernet from a network that aggregates a lot of customers.

the network is not layer 2 , it needs the switch or something else that gets the frame and switch according the destination mac so it can send the frame back .

is it possible ?

Peter Paluch Sat, 09/05/2009 - 13:22
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What do you mean when you say that "the network is not layer 2"? What kind of technology is it? Do you need a routing switch?

In Ethernet networks, it is not only unnecessary to send a frame back the port through which it was received, it would also cause duplicated frame delivery and switching loops. If a switch receives a frame and learns that the destination is on the same port through which the frame came in, then it means that the destination already must have received that frame.

Please try to be more descriptive. If you can explain us some example step-by-step, that would make your issue more easy to understand.

Best regards,


yoram12345 Sat, 09/05/2009 - 20:06
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hi Peter,

The network is MPLS technology.

i have a service of P2MP that connecetd that switch to this network.

the service are passing thrugh p2p tunnels.

because of this MPLS i have the split horizon that prevent from a frame that egress a tunnel to ingress a second tunnel in the same service.

currently i get communication between the users and the device that is locatd after the switch which is VoIP soft switch,but communication between users is not accomplished.

what i need is that the switch will do the following :

either send back the frame that belong to the netork below the switch or send back the ip packets that belong to the below switch, the other ip should be router regulary,

Is it possible ?



Peter Paluch Sun, 09/06/2009 - 00:24
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I am starting to catch up on your issue but still I do not have enough information. Is it perhaps possible for you to create a diagram or a drawing of your topology (the best would be both physical and logical) than is concerned with your issue and would visualize where are the tunnels, where they are terminated, what is the position of the switch and the clients and so on.

Also, you have said that you are using a MPLS technology based on P2P tunnels. Are you using Layer2 pseudowires?

Best regards,



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