Server disappears from network

[Scott Johnson]

I'm running 8.0-release on a Supermicro X7SPA-H with dual GbE. I have
the two interfaces bridged (using if_bridge) with em0 connected to my
PC and em1 to a 100Mb router.

After days of uptime, em1 will suddenly stop responding to anything. I
cannot ping it from the router, and I cannot ping the router from the
console. I can ping the server from my PC and vice versa, so em0 is
still working. Nothing unusual appears in /var/log/messages.

>From the console, I ran `ifconfig em1 down; ifconfig em1 up` and got
this error:
em1: Could not setup receive structures

Which seems to have to do with mbufs. So I upped kern.ipc.nmbclusters
from 32768 to 65536. The next time it went down, I ran `ifconfig em1
down; ifconfig em1 up` again and everything was good. So increasing
nmbclusters helped with something.

After that, I ran netstat -m:

45866/20524/66390 mbufs in use (current/cache/total)
45727/19809/65536/65536 mbuf clusters in use (current/cache/total/max)
43366/591 mbuf+clusters out of packet secondary zone in use (current/cache)
0/260/260/12800 4k (page size) jumbo clusters in use (current/cache/total/max)
0/0/0/6400 9k jumbo clusters in use (current/cache/total/max)
0/0/0/3200 16k jumbo clusters in use (current/cache/total/max)
102920K/45789K/148709K bytes allocated to network (current/cache/total)
0/3538/1768 requests for mbufs denied (mbufs/clusters/mbuf+clusters)
0/0/0 requests for jumbo clusters denied (4k/9k/16k)
0/0/0 sfbufs in use (current/peak/max)
0 requests for sfbufs denied
0 requests for sfbufs delayed
2 requests for I/O initiated by sendfile
0 calls to protocol drain routines


And I ran ifconfig:

em0: flags=8943<UP,BROADCAST,RUNNING,PROMISC,SIMPLEX,MULTICAST> metric 0 mtu 1500
    options=98<VLAN_MTU,VLAN_HWTAGGING,VLAN_HWCSUM>
    ether 00:25:90:02:16:54
    media: Ethernet autoselect
    status: no carrier
em1: flags=8943<UP,BROADCAST,RUNNING,PROMISC,SIMPLEX,MULTICAST> metric 0 mtu 1500
    options=98<VLAN_MTU,VLAN_HWTAGGING,VLAN_HWCSUM>
    ether 00:25:90:02:16:55
    media: Ethernet autoselect (100baseTX <full-duplex>)
    status: active
lo0: flags=8049<UP,LOOPBACK,RUNNING,MULTICAST> metric 0 mtu 16384
    options=3<RXCSUM,TXCSUM>
    inet6 fe80::1%lo0 prefixlen 64 scopeid 0x3 
    inet6 ::1 prefixlen 128 
    inet 127.0.0.1 netmask 0xff000000 
bridge0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> metric 0 mtu 1500
    ether 00:25:90:02:16:54
    inet 192.168.1.93 netmask 0xffffff00 broadcast 192.168.1.255
    id 00:00:00:00:00:00 priority 32768 hellotime 2 fwddelay 15
    maxage 20 holdcnt 6 proto rstp maxaddr 100 timeout 1200
    root id 00:00:00:00:00:00 priority 32768 ifcost 0 port 0
    member: em1 flags=143<LEARNING,DISCOVER,AUTOEDGE,AUTOPTP>
            ifmaxaddr 0 port 2 priority 128 path cost 2000000
    member: em0 flags=143<LEARNING,DISCOVER,AUTOEDGE,AUTOPTP>
            ifmaxaddr 0 port 1 priority 128 path cost 2000000


Is there anything in there that stands out? I don't know enough about
the network stack to interpret much of anything in there.

What can I do to further diagnose this problem next time it happens?
The only other computer on the network is my WinXP desktop.