Networking – Can’t ping LAN machines while on wired connection

In Windows, hostname resolution is generally done using one of four methods:

1. DNS – the most likely option. Your university's DHCP server provides you with DNS servers and with a default suffix that is automatically appended to all bare hostnames. For example, if you ping foobar, and the DHCP server gave you example.edu, Windows will try foobar.example.edu first.

2. NBNS aka NetBIOS – this is an obsolete name resolution protocol using broadcasts. It does not work across routers, and it is highly unlikely that it is used in an university network.

3. WINS – same as NBNS but using a central server. Obsolete in favor of DNS, but still used in some places due to relative simplicity.

4. LLMNR – a newer Microsoft protocol using multicast packets. I don't know how to use it, but it's unlikely to be the cause, as only Windows Vista and 7 support it.

To find out whether DNS is being used, connect your computer directly to Ethernet, then run ping hostname. If you see "Pinging hostname.example.edu", then the name was resolved by DNS, and you have to use the "example.edu" suffix.

A better way to find out which protocol is in use is to run ipconfig/flushdns and nbtstat -R to flush the caches, start a Wireshark capture, and try pinging a valid hostname. (Again, must be connected directly to the Ethernet.)

When using your own DHCP server, you will have to manually configure Windows to use a DNS suffix. In Control Panel → Network and Sharing Center, click the Change adapter settings item. Right-click your network adapter, select Properties → TCP/IPv4 → Properties → Advanced → DNS, and update "DNS suffix for this connection". Alternatively, configure your router's DHCP server to give the correct suffix.

Thank you for the direction, I am going to have to come up to speed on a few things, to work on the advice, but for now

The SPI firewall on DD-WRT machine is disabled There are no Security Policies in place on the DD-WRT router (in the Security Tab) DMZ, QOS are disabled WAN is Disabled DHCP is disabled Advanced Routing is set to Router Mode

The Firewall and all other security on the Arris CM is off (for testing) RoutedwithNAT is on in LAN Settings DHCP pool starts at x.x.x.05

One other fact I discovered this afternoon is that though DD-WRT has the option to make the uplink port just a regular port when DHCP and WAN are disabled - and according to the wiki on WRT the connection should be lan-lan port, NOT uplink port, I only get internet on the M1 and M2 when the cable from the CM is plugged into the uplink port, not any other port, even though the uplink port is supposed to be just a regular port. So its as if the Netgear is not taking the WRT setting, or the Arris won't recognize a connection to any other port.

Even stranger is WIRELESS connections (droid phone) through the netgear router (diff SSID than Arris CM) will ping through to M2 and it has internet - so its just the two wired machines that cannot see each other;

For completeness M1 and M2 are both running Lubuntu 12.10 and have no security/firewall policies that I know of turned on. I am going to revisit local firewall settings as I can't see anything else in WRT that can be changed. I appreciate the help, the best I have gotten at DD-WRT is "it should work if you followed the tutorial"