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[resolved] Server Unreachable from external IPs
I have been trying to setup a counter strike source dedicated server in CentOS 5 over the past few days, but no one outside of the local network is able to connect. The server is sitting behind a router with DMZ enabled on the server's internal IP address.

Here are the arguments used on startup:
./srcds_run -console -game cstrike +map de_dust2 +ip +maxplayers 10 -autoupdate

When the source server is running, issuing
netstat -anp | grep src
returns the following:

tcp        0      0*                   LISTEN      5876/srcds_linux    
udp        0      0*                               5876/srcds_linux    
udp        0      0*                               5876/srcds_linux    
udp        0      0*                               5876/srcds_linux    
udp        0      0*                               5876/srcds_linux    
unix  3      [ ]         STREAM     CONNECTED     126753 5876/srcds_linux    
unix  3      [ ]         STREAM     CONNECTED     126752 5876/srcds_linux    
unix  3      [ ]         STREAM     CONNECTED     126750 5876/srcds_linux    
unix  3      [ ]         STREAM     CONNECTED     126749 5876/srcds_linux

This appears to indicate that the server is listening on the correct ports, and I have opened these ports along with many others within the firewall. Running the command
iptables -L
returns the following:

Chain INPUT (policy DROP)
target     prot opt source               destination        
ACCEPT     all  --  anywhere             anywhere            
ACCEPT     all  --  anywhere             anywhere            state RELATED,ESTABLISHED
ACCEPT     tcp  --  anywhere             anywhere            tcp dpt:ssh
ACCEPT     udp  --  anywhere             anywhere            udp dpts:27000:27020
ACCEPT     udp  --  anywhere             anywhere            udp dpt:scol
ACCEPT     tcp  --  anywhere             anywhere            tcp dpts:27000:27050
ACCEPT     udp  --  anywhere             anywhere            udp dpts:27000:27050
ACCEPT     udp  --  anywhere             anywhere            udp dpt:26901
ACCEPT     tcp  --  anywhere             anywhere            tcp dpt:scol

Chain FORWARD (policy ACCEPT)
target     prot opt source               destination        

Chain OUTPUT (policy ACCEPT)
target     prot opt source               destination        

Chain RH-Firewall-1-INPUT (0 references)
target     prot opt source               destination

Disabling iptables altogether via the command
service iptables stop
does not fix the problem either.

Connecting to the server from one of the computers on the local network attached to the same router as the server seems to work fine. However, when attempting to connect to the server from the external IP, it doesn't work even though the correct port is accessible. Also, connecting to any of the other ports open in iptables (like ssh, ftp, etc.) works just fine. Running
nmap -sU -p27015
from a computer on an external network yields the following results:

Starting Nmap 4.75 ( ) at 2012-01-08 21:59 Central Europe Standard Time
Interesting ports on (
27015/udp open|filtered halflife

Nmap done: 1 IP address (1 host up) scanned in 2.24 seconds
indicating that UDP port 27015 is open and reachable.

I've read seemingly every forum post regarding this issue, yet none of the proposed solutions seem to work. At first I thought that because the process has bound itself to the internal network IP (, only local connections were being accepted. However, changing the server's start up command to bind to an IP of (wildcard) did not work either.

Any one have any ideas?

I've figured out that the problem lies with the router (with dd-wrt firmware). Even though I had DMZ enabled, the correct ports were not being forwarded. I'm assuming when you enable DMZ on a router with dd-wrt firmware, it simply forwards a default range of ports (something like 1-1024). Thus the port ranges corresponding to the counter strike server (27000-27050) were not being forwarded. I have since manually forwarded the correct port ranges in the router and everything seems to work perfectly.

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