Chance Whaley wrote:
split-horizon states that you never should send information about a route back in the direction from which it came. Typically, this is only applicable to DV protocols and the like, but has meaning elsewhere. People have long ignored the rules of split horizon for routing, ie. Frame Relay networks. With the right configuration it really isnt an issue.
But now for the hosting environment its even less meaningfull. In the private VLAN concept, communites of interest (for lack of a better term) are manually created, that allow a given port to only speak (L2) with the router port, and any other ports in its community. For the simple hosting environment its perfect. Everyone is assigned out of the same addressing block, regardless of the order in which the cages/servers were turned up.
A caveat: Be very, very sure that you know what 'simple' means.
This is probably not the greatest solution for colo providers hosting cages and interconnects. But for a simple webfarm and hosting operations its very workable.
My $0.02. From someone who as implemented them, and likes them very much.
I like them (well, Extreme Networks' take on it at least) very much in theory, but am much less pleased with them in practice. If you're considering utilizing private VLANs, I would strongly suggest that you are completely familiar with all the special setups your customers will want in the future, you make it very clear that adding additional servers may force them to renumber. (This is especially important when a formerly simple hosting customer decides to implement load-balancing/firewall/other.) If you are only doing low end web-hosting or single-server colocation, this should work very well. If you're doing network hosting or anything at all complex, consider sticking with standard VLANs. If I were to build a large hosting facility, I would have a low end room with private VLANs for hosting at a discount, and everything else using standard VLANs. My $0.02. From someone who has been through this and now gets to suffer as a customer rather than a provider. Jeremiah