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I'm dealing with a RHEL version 6.4 server's firewall setting and the goal is to allow remote device to connect tcp port 6162, regardless of the type of services.

The iptables rules are shown below(iptables -L --line-numbers), and service iptables has been restarted.

num target prot opt source destination 1 ACCEPT all -- anywhere anywhere state RELATED,ESTABLISHED 2 ACCEPT icmp -- anywhere anywhere 3 ACCEPT all -- anywhere anywhere 4 ACCEPT tcp -- anywhere anywhere state NEW tcp dpt:ssh 5 ACCEPT tcp -- anywhere anywhere state NEW tcp dpt:6160 6 ACCEPT tcp -- anywhere anywhere state NEW tcp dpt:patrol-coll Chain FORWARD (policy ACCEPT) num target prot opt source destination Chain OUTPUT (policy ACCEPT) num target prot opt source destination

Also, I did set the port I want in sytem-config-firewall, as shown figure below. enter image description here

The strange thing is:

No matter how I set the firewall/iptable, the port 6162 just couldn't be opened. It has been tested with telnet client of windows/linux remote hosts that are residing in the same IP subnet of this RHEL 6.4 server. The connection to port 6162 is refused but others worked(such as port 6160).

Tcp port 6162 seemed to be always "patrol-coll" but strictly speaking, I wanna allow any type of services to connect the 6162 port, not just "patrol-coll". Don't know whether the service type does impact on the connection...

Can anyone please provide some hints to troubleshoot the OS-side problem of the connection please?

Notes1: the output of netstat -tulpn is shown below.

Proto Recv-Q Send-Q Local Address Foreign Address State PID/Program name tcp 0 0 0.0.0.0:111 0.0.0.0:* LISTEN 2538/rpcbind tcp 0 0 192.9.110.1:1521 0.0.0.0:* LISTEN 4806/tnslsnr tcp 0 0 0.0.0.0:37426 0.0.0.0:* LISTEN 4493/ora_d000_SOGOE tcp 0 0 0.0.0.0:22 0.0.0.0:* LISTEN 2917/sshd tcp 0 0 0.0.0.0:46775 0.0.0.0:* LISTEN 4686/ora_d000_SOGOL tcp 0 0 127.0.0.1:631 0.0.0.0:* LISTEN 2737/cupsd tcp 0 0 127.0.0.1:10808 0.0.0.0:* LISTEN 3126/veeamservice tcp 0 0 127.0.0.1:25 0.0.0.0:* LISTEN 3007/master tcp 0 0 127.0.0.1:6010 0.0.0.0:* LISTEN 4046/sshd tcp 0 0 127.0.0.1:199 0.0.0.0:* LISTEN 2869/snmpd tcp 0 0 0.0.0.0:37449 0.0.0.0:* LISTEN 2657/rpc.statd tcp 0 0 :::111 :::* LISTEN 2538/rpcbind tcp 0 0 :::6160 :::* LISTEN 2886/veeamdeploymen tcp 0 0 :::40976 :::* LISTEN 2657/rpc.statd tcp 0 0 :::22 :::* LISTEN 2917/sshd tcp 0 0 ::1:631 :::* LISTEN 2737/cupsd tcp 0 0 ::1:25 :::* LISTEN 3007/master tcp 0 0 ::1:6010 :::* LISTEN 4046/sshd udp 0 0 0.0.0.0:111 0.0.0.0:* 2538/rpcbind udp 0 0 127.0.0.1:2547 0.0.0.0:* 4495/ora_s000_SOGOE udp 0 0 0.0.0.0:631 0.0.0.0:* 2737/cupsd udp 0 0 0.0.0.0:1017 0.0.0.0:* 2538/rpcbind udp 0 0 127.0.0.1:13179 0.0.0.0:* 4660/ora_pmon_SOGOL udp 0 0 10.50.89.26:123 0.0.0.0:* 2925/ntpd udp 0 0 192.9.110.1:123 0.0.0.0:* 2925/ntpd udp 0 0 127.0.0.1:123 0.0.0.0:* 2925/ntpd udp 0 0 0.0.0.0:123 0.0.0.0:* 2925/ntpd udp 0 0 0.0.0.0:28426 0.0.0.0:* 4672/ora_lgwr_SOGOL udp 0 0 0.0.0.0:18843 0.0.0.0:* 2657/rpc.statd udp 0 0 0.0.0.0:161 0.0.0.0:* 2869/snmpd udp 0 0 127.0.0.1:22464 0.0.0.0:* 4688/ora_s000_SOGOL udp 0 0 0.0.0.0:9798 0.0.0.0:* 4479/ora_lgwr_SOGOE udp 0 0 0.0.0.0:713 0.0.0.0:* 2657/rpc.statd udp 0 0 127.0.0.1:48982 0.0.0.0:* 4467/ora_pmon_SOGOE udp 0 0 127.0.0.1:26208 0.0.0.0:* 4686/ora_d000_SOGOL udp 0 0 127.0.0.1:54112 0.0.0.0:* 4493/ora_d000_SOGOE udp 0 0 :::111 :::* 2538/rpcbind udp 0 0 :::1017 :::* 2538/rpcbind udp 0 0 fe80::20c:29ff:fe74:83b5:123 :::* 2925/ntpd udp 0 0 fe80::20c:29ff:fe74:83bf:123 :::* 2925/ntpd udp 0 0 ::1:123 :::* 2925/ntpd udp 0 0 :::123 :::* 2925/ntpd udp 0 0 :::46340 :::* 2657/rpc.statd```
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  • if you run netstat, you can see something listening on that port? Commented Aug 1, 2023 at 4:10
  • @JaromandaX I put it into the content. Couldn't find port 6162. Commented Aug 1, 2023 at 6:04
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    what do you expect to be listening on port 6162? If nothing is listening on that port, then how can anything connect to that port? Commented Aug 1, 2023 at 6:08

1 Answer 1

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Your port 6160 works because it seems to have a Veeam Installer Service running (process name is something like veeamdeploymen* according to your netstat -tulpn output).

Because there is no service running on port 6162 yet, the port will not open, although you seem to have already have unblocked it in firewall settings.

Although someone might say "open a port in a firewall", that is a bit of a misnomer: a firewall does not really open ports, instead it can block them so that a port cannot be accessed even if an application opens it. If you don't have any network services running, all network ports will be closed by the operating system alone, and a firewall cannot change that.

By requiring you to effectively configure any legitimate network port access twice (once to activate the service itself, then to unblock it in firewall settings), a firewall minimizes the risk of accidentally allowing unintended access.

A firewall cannot reliably determine which remote application or service is attempting to connect: even if there was a protocol to allow that, the remote system can always tell lies. The Service field is probably just a human-friendly label assigned for a specific port number, typically in /etc/services.

Some firewall management solutions will also allow pre-defining groups of port numbers as "services", for ease of configuration.

If you want to open the port temporarily for test purposes, the "netcat" utility (package name nc) can do it:

To open port 6162 for an incoming TCP connections:

nc -kl 6162

Or if you want to open the port for UDP packets:

nc -kul 6162

Once the command is stopped (with a Ctrl+C or a kill command), the port will automatically close again as there will no longer be a process present to handle any incoming data. Any data sent to the port over the network connection will be emitted to standard output; if you don't want that, you can append >/dev/null to the nc command lines.

Note: the port TCP/6162 is the default port for Veeam Data Mover, however the fact that your system indicates a service name of patrol-coll suggests some other software might (once have) be(en) configured to use that port. (Perhaps a statistics collector of BMC Patrol monitoring software?)

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