RV130 won't pass http unless behind another NAT

Question

I'm attempting to replace a Linksys WRT54G with a Cisco RV130 for a home internet connection. For the moment, the setup is about as simple as it gets. Cable-modem -> RV130 -> Switch -> Multiple computers.

Unfortunately, web traffic and just about everything else is failing or really slow. Ping and DNS resolution work. Packet captures show that the connection is set up (SYN, SYN/ACK, ACK), but the response to any request takes minutes if it ever returns. This applies to packet captures both pre and post NAT (via port duplication on the RV130.

However, if I install the RV130 behind the WRT54G, all is good. No problems whatsoever.

The only setup done on the RV130 is changing the password on the management interface. Otherwise it is in gateway mode (use NAT), firewall wide open.

I've tried multiple reboots of all devices including more than 5 minutes powered off (including the cable-modem itself).

Answer 1

In this case, there were two problems. First, the cable modem remembers the first MAC address it talks to. This is the only mac address it talks to until it gets a reboot long enough to clear it's memory.

The second problem is in the RV130's MAC address spoofing ability. Because the cable modems remember MAC addresses, routers often have the ability to spoof the mac address of the computer you used to test the setup. However, the RV130 does this imperfectly. Only some outgoing packets get the spoofed mac address. These are the only ones the cable modem forwards.

The correct solution in this case was to power off the cable modem for at least 30 seconds and to reset the RV130 to factory defaults.