I’m setting up a bunch pseudo devices. What is the best practice for assigning MACs in a case like this?
IEEE 802.3 defines a reserved bit to indicate locally administered ethernet addresses. Such addresses are much less likely to conflict with physical addresses. You also want to be careful to use a unicast address. In the past, we’ve used addresses of the form 22:00:00:x:x:x because they are both locally administered and use an unassigned OUI.
In order to avoid collisions, I would recommend using a MAC address that has the locally administered bit set: http://en.wikipedia.org/wiki/MAC_address
Basically, the 802 standard includes provisions for locally administered addresses versus universally administered addresses. If the second bit transmitted on the wire is a 1, then the address is considered locally administered. If the second bit is a 0, then address is globally administered and the first 24-bits must be a globally unique OUI assigned by the IEEE.
ExtraHop SEs and Support Engineers typically use MAC addresses that start with 22:00 for pseudo devices. I would suggest standardizing on that convention, unless that causes some conflict in your environment.