Re: Cat 6k Private VLANs - was RE: SUMMARY: bw usage?

[Jeremiah Kristal <jkristal () on2 com>]

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