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How do I set the promisc mode on for a switch. I have two SW like below:

root@chandler:~# brctl show
bridge name     bridge id               STP enabled     interfaces
br0             8000.622c9e9e5b84       no              veth2
br1             8000.5275171ffe82       no              veth20
                                                    veth21
                                                    veth30
                                                    veth31

But I don't know how to put them in promisc mode:

root@chandler:~# ip link show br0
144: br0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UNKNOWN
link/ether 62:2c:9e:9e:5b:84 brd ff:ff:ff:ff:ff:ff

What is the command for that, and should it be executed for the interface(s)?

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2 Answers 2

up vote 2 down vote accepted

In a Linux based switching device, do the following on the interfaces:

ifconfig [interface] promisc

From the man pages:

[-]promisc : Enable or disable the promiscuous mode of the interface. If selected, all packets on the network will be received by the interface.

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I do not think that the bridge interface is supporting PROMISC flag. Try to set the PROMISC on the ethernet interfaces.

Promiscuous mode is not interesting in a switched networking (as opposed to hub/repeater/bus/WiFi based one). So I think that you should reformulate the question for the problem you are trying to solve.

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I can't figure out what it would mean for a bridge to be in promiscuous mode. Promiscuous mode is about how you handle packets not sent to your hardware address and a bridge doesn't have a hardware address. –  David Schwartz Dec 22 '11 at 0:33
    
The interfaces added to the bridge are in promiscous mode. Otherwise it would not possible to listen for traffic that is not addressed to the host. The bridge interface is connected on one side to the host and on one side to the bridge and it is used to allow the host to communicate with the hosts connected to the bridge interface. –  Mircea Vutcovici Dec 22 '11 at 0:45

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