2011/05/08

TCP MSS adjustment on Vyatta 6.2

Recently I found Vyatta 6.2 supports TCP MSS configuration;

Vyatta Release 6.2-2011.02.09
ENH: Allow configuration of TCP MSS and "clamp-mss-to-pmtu" option in netfilter
So I've setup configuratin below to adjust TCP MSS 1200 bytes.

firewall {
    modify mss-test {
        default-action accept
        rule 1 {
            action modify
            modify {
                tcp-mss 1200
            }
            protocol tcp
            tcp {
                flags SYN
            }
        }
    }
}
interfaces {
    ethernet eth0 {
        address 192.168.1.250/24
        firewall {
            out {
                modify mss-test
            }
        }
        hw-id 00:0c:29:xx:xx:xx
    }
    ethernet eth1 {
        address 192.168.2.1/24
        hw-id 00:0c:29:xx:xx:xx
    }
    loopback lo {
    }
}
 
It seems that this configuration worked properly.

Reference
Network/Vyatta - K'Room.net (Japanese)
Vyatta.org :: View topic - vyatta to cisco
Bugzilla – Bug 5309 ENH: Allow configuration of TCP MSS and "clamp-mss-to-pmtu" option in netfilter