FreeBSD Multicast Ethernet Address

Question

I'm trying to recreate a setup used in a paper (this one to be precise). It has two servers behind a switch, which also has a client attached.

I am using three FreeBSD VMs - one for the switch and two for the routers. The client is my Linux host. I have got to the point where the switch VM can route traffic to and from the servers and the host. The paper then describes the following steps:

• Virtual NICs are created using IP aliasing on both servers. These are assigned the same IP address.
• Both servers are also associated with a multicast Ethernet address.
• There is a static ARP entry created on the client mapping the IP address to the Ethernet address.

I have completed the first of these steps and am pretty sure I can do the third no bother, but I am struggling with the middle one. I cannot find many resources relating to multicast setups, and less on a multicast Ethernet address. Does anyone have any experience in this area? Any help would be appreciated, thanks.

The end result is that both servers receive the same TCP traffic at the same time - if there is a different way to accomplish this, I would be happy to hear that too.

Answer 1

I can't access the paper to which you refer but depending on what you want to achieve you could:

1) use ifconfig to change the "link" (MAC) address of your ethernet card to a multicast address. Note that this will replace your existing MAC address (at least till power cycle).

2) You could add a second MAC address by playing with ng_eiface and a bit of fiddling.

3) You could write a program to join a multicast group such that the ethernet card would listen for packets with the multicast address you were interested in.

I'm not 100% sure what you are trying to achieve but maybe one of these is what you want or will lead you in the right direction.