I can SSH and HTTP, but not ping or access particular UDP services over my LAN

Question

So I've encountered a weird problem when trying to set up a Linux server running a variant of CRUX Linux. I am trying to configure it to be a Teamspeak server, but no clients can connect. The machine is on, I can SSH into it and access HTTP(S) services, and another TCP server program but I cannot ping the machine except from itself. The box is set to respond to ICMP requests, and this is the result of iptables:

Chain INPUT (policy DROP)
target     prot opt source               destination         
ACCEPT     all  --  anywhere             anywhere            
ACCEPT     tcp  --  anywhere             anywhere            tcp dpt:ssh 
ACCEPT     tcp  --  anywhere             anywhere            tcp dpt:http 
ACCEPT     tcp  --  anywhere             anywhere            tcp dpt:25565 
ACCEPT     all  --  anywhere             anywhere            state RELATED,ESTABLISHED 
ACCEPT     tcp  --  anywhere             anywhere            tcp dpt:https 

Chain FORWARD (policy ACCEPT)
target     prot opt source               destination         

Chain OUTPUT (policy ACCEPT)
target     prot opt source               destination

I have also tried adding an explicit rule to iptables for the port for teamspeak (9987) using:

iptables -A INPUT -p udp -s 0/0 --dport 9987 -j ACCEPT

but this makes no difference to the ability to connect.

It seems like this is a network problem, but it's weird since the computer has an internet connection; it can ping other machines on the network; and I can access some of the services on it, but not, it seems, ICMP or UDP ones.

Answer 1

Your INPUT policy is "DROP", so anything not matched by any of the rules above will be dropped. We'd need the -v option to iptables to see what the first INPUT rule is. Or better, show the output of iptables-save. Their may also be something interesting in the nat and mangle tables.