CentOS 5 Server :: Port Configuration - Being Blocked - Iptables And Connection
Jul 4, 2009
I have a fresh installation of CentOS 5 I'm using for a server, and I'm having issues with port configuration. I have iptables running, and it started with no /etc/sysconfig/iptables file. I added a few basic rules (port 53, port 10000 for webmin), saved the file, and restarted the service. I tried connecting to webmin, scanned ports, and traffic was blocked. I set iptables to allow all traffic and restarted the service, and it still showed basically every port as being blocked. It seems port 80 and port 22 work for some reason, even when I tell iptables to block all ports.
I'm not sure what's going on here. Iptables is reading the /etc/sysconfig/iptables file, and if I use lynx localhost:someport it responds as it should according to the file. However, if I try connecting by IP, it's like there's some other firewall or something running that does whatever it's configured to do.....
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Mar 25, 2010
I have a mail server on which I would like to block port 25 on my eth0 for everyone except our external spam filter. the problem is that I want our users to be able to connect via port 10025 which is forwarded to port 25, which then is blocked...
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Jan 20, 2010
I get today a server with CentOS.. and someone told me to block access to port 22 for all IP's except my.. so I did
Code:
iptables -A INPUT -p tcp -s my_ip --dport 22 -j ACCEPT
and after
[code]...
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Oct 11, 2010
Strange issue here when trying to verify firewall on Server 8.04. No ftp service running at all on server, but both nmap and netcat report port 21 as being open, even though it isn't.I am 100% sure that port 21 is not actually accessible and iptables rules are fine. Trying to connect to the port fails, yet nmap and netcat seem to report a "false positive"?Have also checked on a number of other servers I'm running, and this "false positive" seems to apply to all of them.
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Aug 1, 2011
I have 2 servers..
let say server A and server B
On server A open ssh is configured and is running on port 2298. So from my machine I can login there using ssh on port 2298
But when I login to server B and from there I try to connect to server A I cannot.
ssh: connect to host <ipaddress here> port 2298: Connection refused
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Oct 21, 2010
VERY new to linux, erm but I have an issue that needs solving!I recently moved to university, where their network blocks sftp port 22, this means that I cannot connect to my FTP server which is running a version of linux.Now I've got this ftp server connected to a seedbox and it was created using the following walk through..Code:I have written this guide for a friend, but I though it would be useful for others as well.
There are several guides floating around, but I found that most always cock up in some way. This one is tried and tested to work on Debian Etch (on an OVH rps, but should apply to most servers).If there is a new stable release of rtorrent/libtorrent then I will update this guide to show you how to update it (without reinstalling the whole server).
At the bottom there are also instructions to install ftp access & some network monitoring software.Basically, I would really like someone to be able to construct the commands on how to change the listen port for sftp connection on linux or add another port to the list that Linux would use so that I could put in through putty.
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Apr 27, 2011
I'm trying to open up some ports to connect via vnc to a server running Centos 5.5. I've edited /etc/sysconfig/iptables everything *looks* fine, but I still can't seem to get access to the port I've opened (I added some newlines for clarity between commands):
[Code]....
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May 17, 2010
Last night I installed all the updates that were available for CentOS. Today, I discovered that all connections to port 25 (Sendmail) are being blocked except connections coming from localhost.
I tried disabling the firewall to see if anything would change but it is still blocked.
If it is not the firewall doing the blocking, what else might it be?
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Jul 10, 2011
Recently I discovered that we were accidentally running a POP server (port 110), when we only should have been running the encrypted version thereof (port 995). This wouldn't have been a problem if the port was blocked in the first place.Isn't the default iptables setup on CentOS to block unspecified ports? Specifically, this line from /etc/sysconfig/iptables
-A RH-Firewall-1-INPUT -j REJECT --reject-with icmp-host-prohibited
Right? Well, this doesn't seem to be working for me. I added some rules to allow additional ports and commented out a couple (crucially port 110), but for some reason, port 110 is open.Here is /etc/sysconfig/iptables and the output of iptables -L below that:
# cat /etc/sysconfig/iptables
# Firewall configuration written by system-config-securitylevel
# Manual customization of this file is not recommended.
*filter
:INPUT ACCEPT [0:0]
[code]....
Why isn't "-A RH-Firewall-1-INPUT -j REJECT --reject-with icmp-host-prohibited" doing what I think it should be doing?
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Jan 28, 2011
I have Linux server (centos) in my company , Network is shared through this linux squid proxy server to Windows client .
How to open port 995 and 587 for Windows client because Outlook are not working in Windows Client ...
How to open this port for Windows Client.
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Aug 5, 2009
If I forward port 80 to port 3128 for squid with an iptable rule, does port 3128 have to be open on the firewall or is this all routed behind the firewall?
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Jul 15, 2011
i want if a port (exp. 1001) have 20 connections that the next new connection forword to an other port (exp. 1002).
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Feb 2, 2010
I am configuring an internal only IMAP server for archival emails. I am absolutely baffled why my connection is being refused. UFW is disabled and IPTABLES has a rule to allow all connections on 143 and 993. When I telnet this response is given:
Code:
telnet localhost 143
Trying 127.0.0.1...
telnet: Unable to connect to remote host: Connection refused
Even nmap shows the port closed. Here is my iptables rule:
HTML Code:
-A ufw-user-input -p udp -m udp --dport 143 -j ACCEPT
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Jan 11, 2011
I am at a loss how to prevent Denial of Service attacks to port 25 and not block legitimate connections from 2 Barracuda 800(s) and block smart phones such as iPhones/Blackberrys/iPhones that use the server smtp.server.com for email.
Presently for port 25
RH-Firewall-1-INPUT -p tcp -m state --state NEW -m tcp --dport 25 -j ACCEPT
The 2 Barracuda 800(s) make port 25 connections all the time, plus users with smart_phones have the incoming server type:
IMAP
pop.server.com
smtp.server.com
Is there a way to keep Denial of Service attacks from happening with iptables rules without causing blocking to the Barracuda(s) that make constant port 25 connections & smart phones that poll? I was thinking if I allowed the Barracuda(s) in these lines
-s (barracuda)24.xx.xx.xx -d (emailserver)24.00.xx.xx -p tcp -m tcp --dport 25 -m state --state NEW -j ACCEPT
Where the source would be the Barracuda going to the email server. It would be allowed, then I am left with how to allow other connections like Smart_Phones that connect via Port 25. I am thinking if I put rules in place doing connection counts in a minute it would result in errors connecting to the server and people would start complaining. Plus any limiting may result in blocking real traffic. Then would I need to allow the ISP range in the above example to accept port 25, I am still left with how to drop a flood/denial of service attack.
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Jul 14, 2010
I've recently turned an older PC into a linux box for the purpose of creating an online server with ftp and ssh capability and file sharing. I've installed Kubuntu 9.10 and I'm trying to ssh to the computer from outside the network.I've install the openssh-client and openssh-server and I've created a static ip address, which works fine. I cannot ssh to the machine from outside the isp using either the direct ip address or hostname. The machine is connected to the internet via a Linksys Wireless G router, and I've edited the configuration settings to keep port 22 open for connect in the port server utility.
I've checked the ssh_config and sshd_config settings and port 22 is the default connection port, which is supposed to be open. I've run ifconfig and everything looks fine. I can connect to the computer using a machine connected to the same router, but other computers cannot access it. I want it to be visible to everyone.
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Dec 24, 2010
I'm trying to open port 119. I already have a few ports open. I've used webmin to open both incoming and outgoing ports. iptables --list --numeric gives me:
Code:
...
ACCEPT tcp -- 0.0.0.0/0 0.0.0.0/0 tcp dpt:10000
[code]....
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Jun 6, 2010
I am new to iptables. The setup tool on a VPS doesn't work. So, I am learning to insert rules. I have inserted so many and some of them show as duplicates now.
1- I want to know how to remove the duplicates. Is there a file that these rules are store in so I can go in and easily edit it?
2- Is there any other utility that handles firewall in Linux that I am unaware of? or is the iptables the ultimate door guard? This is a plain install of CentOS.
3- Since I believe I opened port 5090 but I think it still might be blocked, could SELINUX be the problem? How can I get my way around setting it to permissive or disable if I don't have access to "setup" command?
4- What is the order of iptables reading? does rule #1 supersede all other rules? or does the last rule supersede all rules prior to it?
5- Do the rules below make a fairly safe system? (except for the duplicates which should be remove) I understand that a safe system is dependent also on the applications that are allowed in this category and I am not talking about those. I am talking about dropping all other inquiries and in general is this how iptables are setup? This is what I currently have:
[root@tel ~]# service iptables status
Table: filter
Chain INPUT (policy ACCEPT)
num target prot opt source destination
[Code]...
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Apr 12, 2010
I installed Ubuntu 9.10 and tomcat 6 java servlet container. I am trying to run the tomcat server on port 80, so I edited tomcat's configuration file (server.xml) and changed the default port from "8080" to "80". I launched tomcat server, went to my browser and entered:[url], but it says can not find server/location. Then I edit the server.xml and revert back to port "8080" and then enter: [url] and everything works fine. So my guess is some other service is taking up port 80, but I would think not, since I just installed Ubuntu and made sure apache isn't installed or running.
So I went to "System" --> "Administration", then choose "Network Tools". I then executed Netstat and did not see anything taking up port 80, but I do see port 8080 taken (assuming it is the tomcat server). Then I also did a Port Scan and entered my IP number. Again, I don't see port 80 taken, but do see 8080 being used.
I had a winxp laptop computer behind home wireless and was running tomcat 6 server fine with it, but it over-heated and died recently. So I got a used laptop and just installed Ubuntu 9.10. I have not changed my wireless router settings. It is the same as before. So I have ruled out my home's hardware/network equipment.
So here now I sit, wondering what is up?
For security reasons, is port 80 initially blocked by Ubuntu for some reason? Is there something I have to do beforehand to free up port 80?
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Dec 1, 2015
I'm trying to use these cookie cutter rules that I found. But every time I use them, after a few seconds my wifi connection goes dead. The exception was the first time I used then. Which lasted me a couple of minutes.
By dead I mean I can no longer open a webpage or ping google.
iptables -N LOGGING
iptables -A INPUT -j LOGGING
iptables -A OUTPUT -j LOGGING
iptables -A LOGGING -m limit --limit 2/min -j LOG --log-prefix "IPTables-Dropped: " --log-level 4
iptables -A LOGGING -j DROP
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Mar 26, 2010
I have the following setup and Im trying to forward all incoming connection on port 1194 on eth2 which is the external network to ip 192.168.10.100, but seems its not working.
Current config:
# Generated by iptables-save v1.3.8 on Sun Nov 16 00:00:54 2008
*nat
:PREROUTING ACCEPT [26751696:2175544875]
:POSTROUTING ACCEPT [339911:19096812]
[code]....
plus im adding the prerouting:
iptables -t nat -A PREROUTING -i eth2 -p tcp --dport 1194 -j DNAT --to-destination 192.168.10.100
This configuration doesnt work. I also I have tried:
iptables -D PREROUTING -t nat -p tcp -d XX.XX.XX.XX --dport 1194 -m state --state NEW,ESTABLISHED,RELATED -j DNAT --to 192.168.10.100:1194
and the same its not working. Connecting thru telnet to the domain: telnet mydomain.org 1194 doesnt work, but within the server, running telnet 192.168.10.100 1194 it works.
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Jul 12, 2011
i've got a software that uses a specific tcp port e.g 11111. i want to redirect all the traffic from 11111 to squid port 3128. i'm using the following commands to redirecting:
iptables -t nat -A PREROUTING -p tcp -m tcp -i eth0 --dport 11111 -j DNAT --to 192.168.0.1:3128
iptables -A FORWARD -p tcp -m tcp -i eth0 --dport 11111 -j ACCEPT
my ubuntu server has two interfaces. eth0 is for local network (dhcp assigns ips) and eth1 is for internet. my ubuntu server acts as a gateway and as an authentication server for users.
at squid also i have the following configuration regarding my port:
acl myport port 11111 http_access allow CONNECT myport. my squid installation is not transparent as users need to authenticate in order to access the web.
my application is a windows application and of course is not working. i examined the packets with wireshark and i noticed that when the program tries to access the internet, squid replies with err_invalid_request (the packet contains that data). the program is trying to send some plain text via port 11111 and as far as i can image, somehow squid declines the data. i cant get rid off squid as i want to pass the traffic from squid. what is the problem?
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Mar 9, 2010
I have setup sshd_config for port 3210! I have difficult setup the iptables firewall to allow ssh on port 3210! i always enter this:
iptables -A INPUT -p tcp --dport 3210 -j ACCEPT
iptables -A OUTPUT -p tcp --sport 3210 -j ACCEPT
but after i restart ssh, the system do not allow port 3210... why? do i forget something?
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Nov 9, 2009
I'm using iptables with modules ip_contrack_ftp to be able to use passive ftp. It works well as long as port 21 is being used as listening port. Is there any way to make it work when I configure my ftp server (vsftpd) to listen on an alternative port, lets say 21001 or something? The helper module only seems to be working properly with the standard port, so I was wondering whether there was a way to "tell it" that another port is being used? I mean, of course I make a rule in fw to allow traffic to the alternative port.
But once it's time to start passive connection, then the iptable module cannot handle it properly. I could solve the problem by making a range of passive ports in the ftp-server configuration and allow the incoming traffic to them, but then using helper modules doesn't make any sense. I just want to allow the traffic to the listening port and then want the ip_contrack_ftp module to take care of the rest. This is what I do today - but only port 21 seems to be working. Is there a way to do this with a non-standard ftp port?
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Jan 17, 2011
I sometimes get my webserver blocked by my mysql server because of "to many connection errors" and have to use flush hosts to solve it, i now wonder if there is any way to increese that connection error value so the webserver wont get blocked ?
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Nov 29, 2010
I connect to the internet at work through an authenticating proxy, and to avoid having to enter the proxy info into every app I use (e.g. firefox, wget, kde, etc) I have set up squid as a local transparent proxy which authenticates and routes all traffic to the work proxy. It has been working fine, but lately I haven't been able to connect to any https sites. I don't think I have changed the configuration, so perhaps it is the result of an upgrade, or something badly configured on my system from the start. I have tried connecting to https sites without squid and iptables and it works fine. My system is Arch linux, and my squid.conf file is: Code:
acl all src all
acl manager proto cache_object
acl localhost src 127.0.0.1/32
acl to_localhost dst 127.0.0.0/8
acl SSL_ports port 443
acl Safe_ports port 80# http
acl Safe_ports port 21# ftp
acl Safe_ports port 443# https
[Code]....
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Jul 22, 2010
https://hostname:8834/ is blocked by iptables ?
I have nessus application is running in the target machine and the url
is https://hostname:8834/ - which is not accessible
But when i login in the target machine via ssh and check that this application and the service is running fine So i think it is blocked by the iptables in the same machine, where the nessus is running
find the iptables status when iptables -L
iptables -L
Chain INPUT (policy ACCEPT)
target prot opt source destination
RH-Firewall-1-INPUT all -- anywhere anywhere
ACCEPT tcp -- anywhere anywhere tcp dpt:nessus1
ACCEPT tcp -- anywhere anywhere tcp dpt:nessus1
[Code].....
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Mar 1, 2010
I have got a laptop running Debian squeeze. I wish to share the wireless connection of the laptop (wlan0) to the ethernet port of the laptop, so that I can share the wireless connection to my desktop PC which is connected to the ethernet port.
[My desktop PC]---Ethernet---[My laptop]---))) WiFi )))---[Public network/ ISP]
I have read the article on Ubuntu community: [url]
I followed the steps, and the /etc/network/interfaces file on my laptop is:
Now the situation is: My laptop can connect to Internet (i.e. ping debian.org from laptop is fine), my desktop PC can connect to my laptop (i.e. ping 192.168.1.1 from desktop PC is fine). However, the desktop PC cannot reach the Internet.
I also read the information on Debian Wiki: [url]
It seems I must install and configure ebtables before sharing my wireless connection to ethernet port. Is it true? (But why the article on Ubuntu community doesn't mention it?) Or I just made some mistakes?
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Dec 23, 2010
I'm trying to limit access to port 8443 on our server to 2 specific IP addresses. For some reason, access is still being allowed even though I drop all packets that aren't from the named IP addresses. The default policy is ACCEPT on the INPUT chain and this is how we want to keep it for various reasons I wont get into here. Here's the output from iptables -vnL
[Code]...
Note the actual IP we are using is masked here with 123.123.123.123. Until I can get everything working properly, we're only allowing access from 1 IP instead of 2. We can add the other one once it all works right. I haven't worked with iptables very much. So I'm quite confused about why packets matching the DROP criteria are still being allowed.
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Oct 20, 2010
LinuxA & LinuxB
linuxA:eth0(10.1.1.1) connected linuxB:eth0 (10.1.1.2)
linuxA:eth1(202.1.20.45) connected internet
[code]....
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Apr 18, 2011
Is there any way to verify if packets being trafficked over a certain port are valid for the service you want to use this port for?
One obvious example that probably clarifies my question:
When I open port 443 (outgoing or incoming) for https/ssl traffic, I don't want this port to be used for say openvpn traffic.
Thus: when someone wants to surf to a website with https, it should be ok but if someone wants to connect to his home openvpn server over that same port, it should be blocked.
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