IBM H Chassis populated with HS22 blades
Blades use Broadcom 5709S dual gigabit NIC
With ESXi 5.0, system was running fine with both NICs connected (with static IP) in the management network settings (able to ping in and out). Performed upgrade to ESXi 5.1 preserving VMFS datastore. After reboot, management network shows both NICs connected with static IP still assigned but I haven't any network connectivity (unable to ping in our out). If I disable any one of the NICs, and restart the management network, I can immediately ping in and out.
I have taken a spare blade and tested this by upgrading from 5.0 to 5.1 and installing 5.1 clean, both producing same results. A 5.0 host with both NICs enabled (whether static IP or DHCP) can ping in and out. A 5.1 host with both NICs enabled (whether static IP or DHCP) cannot ping in our out. 5.1 host cannot obtain DHCP address, but fails back to APIPA.