paul@vix.com (Paul Vixie) writes:
There's a fourth. I used to manufacture something called the Web Gateway Interceptor which was topologically a router. It wasn't competitive as a router, either in price, performance, or number/kind of interfaces. But you could put it in parallel with another router and integrate it into your OSPF mesh and use OSPF link costs to make it be the primary path only while it was up. HSRP would have worked the same way, and I'll admit that it's a lot simpler to do (though I'm not sure it's an open standard yet?)
HSRP is published as an Informational RFC. However, there is a patent on the protocol, assigned to Cisco. To the best of my knowledge, Cisco has not granted any licenses to that patent (yet). The VRRP working group selected the VRRP protocol instead of HSRP to place on the standards track, so at this point, it is unlikely that HSRP will become a standard (open or otherwise) anytime soon. Tony