The openbsd project tried to get a protocol number for carp, IANA made it more difficult then the project was able to comply with. so they made an executive decision to use the vrrp protocol number as the least wrong option.
Long story short pay extra close attention when when mixing vrrp and carp on the same network segment.
"The OpenBSD team, led as always by their Glorious Leader (their words, not mine), decided that a RAND license just wasn't free enough for them. They wrote their own protocol, which was completely incompatible with VRRP. Well, you say, that's not so bad; that's competition, and we all know that competition is good and brings better products, and it's the glorious triumph of Capitalism. But there is one last little nit to this story. The new protocol dubbed CARP (Common Address Redundancy Protocol) uses the exact same IP number as VRRP (112). Most people, and KV includes himself in this group, think this was a jerk move. "Why would they do this?" I hear you cry. Well, it turns out that they believe themselves to be in a war with the enemies of open source, as well as with those opposed to motherhood and apple pie. Stomping on the same protocol number was, in their minds, a strike against their enemies and all for the good. Of course, it makes operating devices with both protocols in the same network difficult, and it makes debugging the software that implements the protocol nearly impossible."
It is hard to say, I am not involved in ether project. CARP was definitely created in response to perceived deficiencies(both technical and political) in VRRP. I agree it does sound like picked the same number out of not a little spite. However the openbsd project has this to say about picking the ipnumber.
"As a final note of course, when we petitioned IANA, the IETF body regulating "official" internet protocol numbers, to give us numbers for CARP and pfsync our request was denied. Apparently we had failed to go through an official standards organization. Consequently we were forced to choose a protocol number which would not conflict with anything else of value, and decided to place CARP at IP protocol 112. We also placed pfsync at an open and unused number. We informed IANA of these decisions, but they declined to reply."
Obviously the correct thing to do is get numbers via IANA but what is the least wrong thing to do when your project is too small to do this. Camp on unused numbers? If your project is successful enough they will eventually be granted. Use whatever number matches the closest fit? Pick some screwball assignment that failed to gain any actual use?
