Sigurbjörn Lárusson's blog

Musings of a network engineer


Dealing with Multicast on a regular basis I've often come across an issue of having to convert between a multicast group IP and its corresponding mac-address, or I know the mac-address but I don't know which multicast group address might be behind it.

One of those issues rises when you're configuring something like IGMP snooping static join in which some Cisco switches want the group address and others want the mac-address of the group. Looking this up isn't terribly hard but since I've been doing it a lot lately I wrote a simple tool called mconvert which can convert in both directions, you can use it like this:

  • mconvert -p will tell you what mac-address is used for
  • mconvert -q 0100.5e68.0101 will tell you which group address are possible for 0100.5e68.0101 (32 possible matches)
You can download mconvert.c here. It should compile on any *nix system using just gcc -o mconvert mconvert.c

New Domain Name

This is the first blog post from a new domain name, Hopefully more will be added as I have time. I know the look is quite raw at this point, it will hopefully improve as I have more time to devote to it.