I'm getting excessive TCP Dup ACK and TCP Fast Retransmission on our network when I transfer files over the MetroEthernet link. The two sites are connected by one sonicwall router, so the sites are only one hop away.
Here is a screenshot from wireshark, and here is the entire capture. In this capture, the client is 192.168.2.153 and the server is 192.168.1.101 Here is a traceroute from my system to the server (ping times are usually steady under 10ms):
user@pc567:~$ ifconfig eth0
eth0 Link encap:Ethernet HWaddr 00:e0:b8:c8:0c:7e
inet addr:192.168.2.153 Bcast:192.168.2.255 Mask:255.255.255.0
inet6 addr: fe80::2e0:b8ff:fec8:c7e/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:244994 errors:0 dropped:0 overruns:0 frame:0
TX packets:149148 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:319571991 (319.5 MB) TX bytes:12322180 (12.3 MB)
Interrupt:16
user@pc567:~$ traceroute -n 192.168.1.101
traceroute to 192.168.1.101 (192.168.1.101), 30 hops max, 60 byte packets
1 192.168.2.254 0.747 ms 0.706 ms 0.806 ms
2 192.168.1.101 8.995 ms 9.217 ms 9.477 ms
user@pc567:~$
Any help on what's causing this would be helpful! I can post any more details needed.
UPDATE: Since this started, I've replaced the sonicwall with an 1800 cisco router. The packet capture with it installed had the same results. Since it is a metro ethernet circuit, no router is required. So I've also tried connecting to laptops directly into the service providers equipment at both sites, and putting them on the same subnet. The packet capture looks the same doing it this way. This leads me to believe that there is a problem with the metro ethernet circuit, even though they continue to say nothing is wrong and everything tests ok.