'no buffer space available' after switch goes down on freeBSD 7.3

[Tsaregorodtsev Denis]

Hello,

I maintenance ISP's DNS server which works under FreeBSD 7.3 and BIND 9.9.1-P4. The network adapter is Intel(R) PRO/1000 Network Connection, driver - em. The server is connected to a Cisco 6500 switch. Sometimes the switch goes down (for maintenance) and is unavailable for 10 minutes. After the switch goes up the server is still unavailable through IP. When I open an IPMI console on the server and enter the ping command, I receive "no buffer space available" error message. And the network doesn't work until the server reboot.
I tried to google this and found that the problem can be solved by increasing nmbclusters parameter. But I want to understand why this problem appears when the switch is rebooting . May be you can suggest something?

Best regards, Tsaregorodtsev Denis