Update: As of June 25, 2009, the KB article 897567 has been updated, and now is accurate.
As of June 13, 2009, the content of the KB article 897567 contains an inaccuracy. The last octet for the second MSN IP address was improperly transposed. It’s published as 126.96.36.199, but that should be .245.
We are working on getting the Knowledge Base article updated, but in the meantime, wanted to make our customers aware of this matter sooner rather than later. Unfortunately, Microsoft cannot change the infrastructure to remedy this, as the "incorrect" IP address is already in use for another service in the Messenger cloud.
I will update this blog entry once the KB article has been updated to reflect the correct information.
Just to be clear, we're not using the 188.8.131.52 IP for federation.messenger.msn.com yet so this issue won't be impacting any current traffic.