Bandwidth Troubleshooting

[Gunter Wambaugh]

I have been having this off and on problem with my FreeBSD server for  
some time now, and I haven't been able to track down the cause.   
Bottom line:  network throughput between local boxes is around 200KB/ 
s on a 100MBs network.  This will last for a few hours and then  
quietly return to the ~2MB/s I am used to.  (Speed according to  
scp).  I have used netstat -anf inet, sockstat -4, ps auxww, and top  
to see what is running, but I see nothing obvious.  I do see the  
occasional

fxp0: link state changed to DOWN
fxp0: link state changed to UP

in my dmesg.  Anyone have any suggestions on how to track this thing  
down?

uname -a
FreeBSD gorgoroth.six-two.net 6.0-RELEASE FreeBSD 6.0-RELEASE #1: Sat  
Feb 25 11:25:33 CST 2006     root at gorgoroth.six-two.net:/usr/obj/usr/ 
src/sys/OPTIMIZED  i386


ifconfig
fxp0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1500
         options=8<VLAN_MTU>
         inet6 fe80::206:29ff:fede:51ab%fxp0 prefixlen 64 scopeid 0x1
         inet 192.168.1.106 netmask 0xffffff00 broadcast 192.168.1.255
         ether 00:06:29:de:51:ab
         media: Ethernet 100baseTX <full-duplex>
         status: active
fxp1: flags=8802<BROADCAST,SIMPLEX,MULTICAST> mtu 1500
         options=8<VLAN_MTU>
         ether 00:06:29:de:51:aa
         media: Ethernet autoselect (none)
         status: no carrier
lo0: flags=8049<UP,LOOPBACK,RUNNING,MULTICAST> mtu 16384
         inet6 ::1 prefixlen 128
         inet6 fe80::1%lo0 prefixlen 64 scopeid 0x3
         inet 127.0.0.1 netmask 0xff000000