How does crossbow deal with MAC address conflicts?

When I gave my presentation on Solaris network virtualization a few months back, one of the folks in the audience asked me how Crossbow deals with duplicate MAC detection. I didn’t have a solid answer for the gentlemen that asked, but thanks to Nicolas Droux from Solaris kernel engineering, now I do. Here is what Nicolas had to say about this topic on the network-discuss mailing list:

“When a VNIC is created we have checks in place to ensure that the address doesn’t conflict with another MAC address defined on top of the same underlying NIC. When the MAC address is generated randomly, and the generated MAC address conflicts with another VNIC, we currently fail the whole operation. We should try another MAC address in that case, transparently to the user, I filed CR 6853771 to track this.

To reduce the risk of MAC address conflicts with physical NICs on other hosts on the network, we use by default a OUI with local bit set for random MAC addresses, and we let the administrator use a different OUI or prefix if desired. We currently don’t have a mechanism in place do perform automatic MAC address duplication detection between multiple hosts.”

I was under the impression that Crossbow used the ARP cache and DAD code to verify that a MAC address wasn’t in use on the network, but that doesn’t appear to be the case. Given this new information, I will need to modify my tools to assign a static MAC that is based off of the address assigned to th virtual NIC. Thanks Nicolas for the awesome reply to the list!

This article was posted by Matty on 2009-06-25 08:28:00 -0400 EDT