Arch Linux

pythonist

Member

From: Rome, Italy

Registered: 2007-11-07

Posts: 5

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Masquerading and bridging

Hi all!

Yesterday I migrated my home server to ArchLinux from Ubuntu. I tried to replicate my old configuration but failed to configure my network in the same way as my old Ubuntu box.

Basically, I have two NICs, eth0 and eth1. I've boxes connected to both NICs so I decided to make a bridge out of them (br0). More, my DSL modem is connected to one the two NICs so my home server was configured to start a PPP connection on br0 and to masquerade all the connection from my internal network to ppp0.

Everything worked fine under Ubuntu. As soon as I migrated to ArchLinux, this configuration stopped working. After some hours spent narrowing the problem, I discovered that pulling out of the bridge the NIC where the DSL modem is connected to, makes the whole thing work.

So, there must be some routing issue when the modem's NIC is inside the bridge. I even tried to sniff ppp0 using tcpdump in various configuration. When masquerading is off, I correctly see packets from an internal box with a non-routable source address (i.e. 10.7.x.y). Activating masquerade, the source address changes to the home server's public IP, as expected but, ICMP echo requests don't get any echo reply. Curiously, pinging the same address from the home server produces the same packets which, this time, get an answer from the remote host.

I was forced to change the configuration and I think I've come to a better one in the end. But the issue remains. In my life I configured lots of networks using NAT and MASQUERADING. Anyhow, this is the first time I encounter a problem I can't solve myself.

Thank you all.

Cristiano