After a week of oversized articles, I’ll try to keep this one short. This is a true story someone recently shared with me (for obvious reasons I can’t tell you where it happened ... and no, I’m not making it up). Enjoy!
Unfortunately I was forced to implement L2 DCI for a "virtual DC" supporting between 4000 and 5000 physical servers with a 25:1 to 30:1 virtualization ratio (so a huge environment). Needless to say in less than 12 months of bringing it online the whole thing melted to a broadcast storm, yet my server team peers still can't understand why it's a bad idea :)
Do I have to add that there are usually no good reasons to build a L2 data center interconnect and plenty of time-tested layer-3 solutions including local and global load balancing and path separation with MPLS/VPN.
If you have a war story you’d like to share, send it over – I’ll keep all your personal details confidential (no, I’m not trying to turn this web site into NetworkLeaks, but reading about other people’s experiences can’t hurt).