Multi-vendor strategies [was: Re: Benefits (and Detriments) of Standardizing Network Equipment in a Global Organization]

I'll certainly try.

As one hopefully fairly clear example; at a large (US-nation-wide) metro
Ethernet provider, we standardized as follows:

L3 devices (aka core, customer edge, and Internet/peering edge routers)
were all from Vendor A
- These devices spoke OSPF, BGP, and RSVP with each other.

L2 devices (aka metro ring switches) were all from Vendor B
- These devices spoke STP with each other.

L1 devices (aka optical transport) were all from Vendors C or D (individual
markets got to choose which, but they could only have one each)
- These devices inter-operated with each other at the optical layer.

Basic network security was handled by devices from Vendor E
- These devices collected netflow data and flagged alerts

DNS was handled by software from another vendor on servers from yet another
vendor, etc...

Is that enough detail to be useful?