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i want to get a network device working as a multiplexer.

for example, only the data sent to port A would be forwarded to port B completely. and the data of port B have to be forwarded to port A also. it seems like there is a virtual twister line between port A and port B.

after some configuration, i can dismiss the virtual line of A<=>B. the other virtual line C<=>B can be established.

i need four separate virtual lines described above concurrently. also 20 ports are a base line.

the first solution comes to my mind is a switch with VLAN. but VLAN would involve some tags. any good idea or switch model suggestion?(1Gb ether needed)

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migrated from superuser.com Sep 26 '10 at 8:51

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Please clarify your question. Are you looking for something specifically that will not forward A and C through B at the same time? Or are you saying you want to "combine" the traffic of A and C through B? –  ultrasawblade Sep 26 '10 at 0:27
    
it has been edited. –  Readon Shaw Sep 26 '10 at 2:43
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Sorry, but your edited question still doesn't make sense to me. –  hotei Sep 26 '10 at 3:13
    
it was mirigated from site to site. still have no results. –  Readon Shaw Sep 26 '10 at 8:59
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4 Answers

get a dot1q-aware switch and use the port-based vlan feature

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does port-based vlan add vlan tag to the raw frames? i wonder whether it would change the length of original frames. –  Readon Shaw Sep 27 '10 at 0:51
    
it does, since it will (eventually) leave the switch via the trunk port and needs to be correctly recognized at arrival ... –  petre Sep 27 '10 at 5:39
    
is there any setting can specify vlan engine do not modify the forwarding packets? –  Readon Shaw Sep 27 '10 at 10:53
    
big problem! the switch would filter runt and other error frames, can i disable that? –  Readon Shaw Sep 27 '10 at 14:37
    
I guess not, each frame is tagged with vlan id... –  petre Sep 27 '10 at 14:39
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Can you describe it with more detail and concrete application examples?

If you want to communicate from a host to a whole network but have another port receive everything what the first one transmits/receives; but what you describe has some resemblance to port mirroring; most manged switches can do it. Keep in mind this is layer 2, so to get the data you will need promiscuous mode and an application that can understand this. Just another instance of a Tcp/ip application will not magically make it receive duplicate data.

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a network test experiment, i have a network analyzer plug in switch, it will send out and receive data from net.and i want to choose which port is being tested by program. so dynamic virtual line is needed. –  Readon Shaw Sep 27 '10 at 0:53
    
Then port mirroring is for you –  Joris Sep 27 '10 at 5:51
    
port mirroring just mirror the data from ports to mirroring port, but i need it forward the the data from mirroring port to normal port. –  Readon Shaw Sep 27 '10 at 10:51
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If I read the question correctly, you just need a managed switch that will support port based VLANs. You don't need to worry about tagging or 802.1q. Simply configure the switch with two VLANs. Put port A in the first VLAN and port C in the second VLAN. Then assign port B to the first or second VLAN based on if you want it to connect to port A or port C.

The cheapest switch that I think would meet this that I can find is on newegg.

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i want to get a network device working as a multiplexer. for example, only the data sent to port A would be forwarded to port B completely.

alt text

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plz pay attention to the following desciprtion. –  Readon Shaw Sep 26 '10 at 3:12
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