A firewall is a program that controls the incoming and outgoing network traffic on a system. Use this tag for all questions related to firewall configuration and operation.

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Open UDP Ports; Can I Close Them?

I'm trying to secure my internet browsing. I just reinstalled Xubuntu 14.04 and GUFW firewall. I have 8 UDP ports open. I don't understand why. The software I currently have open are Firefox, GUFW, ...
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What port uses my backportpackage or bzr?

I am working in a company what uses Ubuntu Precise on the desktops behind a proxy. The Proxy is available in /etc/environment and set as: http_proxy, https_proxy, ftp_proxy, no proxy and their ...
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How to use both syn proxy and connlimit rules with iptables?

I want to write both syn proxy and connlimit rules. I want to send packets to syn proxy first because of performance issue. Here is rule sample. I use bridge interfaces but I dont think it is ...
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kernel security and IDS Firewall + AV together or not?

I try to hardening my server. For doing so, I got a general question: Should I install kernel security patches like selinux and an Anti-Virus with Intrusion Detection Firewall? Does it make sense to ...
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How to setup reverse FTP in RHEL?

Researched: http://www.thecave.info/export-proxy-username-password-linux/ http://stackoverflow.com/questions/5334110/text-based-ftp-client-settings-behind-a-proxy ...
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26 views

Which port to open for Google HangOut Video Conference

We need to open the necessary ports for Google Hangout VIDEO Conferencing in our firewall. Unfortunately my netmon trace shows Port 51355 and 51336 to be active; which is not at all what the Google ...
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21 views

How to send all packets passing my firewall device to logging server?

I want to send all packets that pass my firewall device to logging server to inspect contents of passing packets on my logging server. It seems like my device doesn't support that feature explicitly ...
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250 views

Changed SSH port without allowing it through firewall, locked out now - what to do?

I have a VPS where I changed the SSH port from the default 22. Unfortunately I forgot to allow the new port through the firewall. I don't have physical access to the server, and my host does not seem ...
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firewall-cmd forward rules for interface with multiple ips

I'm looking for a way with firewall-cmd or another command to do the following. An incoming public interface has multiple ip addresses bound to it. How can I forward ports only for one of the ip ...
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37 views

iptables: using “conntrack” and “recent” modules to block unsolicited packets

When I only allow RELATED and ESTABLISHED packets, and DROP everything else, my firewall rules work perfectly and I have no problems: ### VARIANT A -A INPUT -i wlan0 -m conntrack --ctstate ...
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what is dhcpv6-client service in firewalld, and can i safely remove it?

In a CentOS 7 server, I type in firewall-cmd --list-all, and it gives me the following: public (default, active) interfaces: enp3s0 sources: services: dhcpv6-client https ssh ports: ...
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blocking all but specific ips from specific services in CentOS 7

In a CentOS 7 web server that needs to remain totally closed to the public, I need to block all ip addresses and then only allow specified ip addresses to access specified services. How can I ...
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52 views

Block all but specified range of ip's input to an specific port [duplicate]

In a CentOS 7 web server, how do I configure firewalld to block all but a specific list of ip addresses from making successful http or https requests? I know that I can use httpd.conf to restrict by ...
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46 views

how to make firewall changes permanent via firewall-cmd?

I am trying to open some ports in CentOS 7. I am able to open a port with the following command: firewall-cmd --direct --add-rule ipv4 filter IN_public_allow 0 -m tcp -p tcp --dport 7199 -j ACCEPT ...
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17 views

libvirtd and filtered ports

I am new to virt-manager. After having configured a virtual network (new interface virbr0) with 2 VMs that should be able to communicate, I discovered that most ports are filtered. For example, the ...
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53 views

Linux Bridge Network with Static IP Addresses and Firewall

any and all help is appreciated. I am trying to set up my Network Map Can you give me advice in setting up my interface file? If I set a static IP on my PLC on the same gateway, I shouldn't need to ...
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37 views

iptables INPUT command

On a machine called ubuntu1, this is the iptables command: sudo iptables -A INPUT -p icmp -j DROP on the other computer (xp1) I can not ping the ubuntu1.So this is OK. But On ubuntu1 can ping xp1. ...
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Initial iptable rule and knockd operation in vps

Today I launched a vps with Debian 7 x64 and started playing around with it. I installed xampp as well as knock daemon to get my hands dirty. So, all I wanted to do was to actually block all requests ...
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iptables is ignoring rules?

I've found some strange traffic through tcpdump (traffic is ongoing always): 13:00:13.203754 IP 1.2.3.4.1028 > 188.113.188.16.56881: UDP, length 103 13:00:13.204396 IP 1.2.3.4.1028 > ...
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163 views

CentOS 7 Firewalld zone configuration for private web application

I have read all the man pages related to firewalld and also explored all of the files that come pre-installed in firewalld before it is configured. How can I configure the zones of the firewall to ...
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28 views

OpenVPN on Ubuntu VM

I am trying to create a VLAN Network from my home network for a web-dev platform. I am running Ubuntu servers in VirtualBox on a Windows 7 machine. I am running an Ubuntu DHCP/OpenVPN/Shorewall ...
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26 views

Iptable forward interfaces for gateway machine

I have two Ethernet interface being configured to use as system gateway ex: eth1: 10.10.1.0 eth2: 10.10.2.0 I want to forward all the packets which are coming to the 10.10.2.0 gateway contacting ...
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71 views

Assp won't start

I tried to install ASSP (Anti-Spam SMTP Proxy Server),but when I try to start it I get the following: $ perl assp.pl Perl version 5.012003 (5.12.3) is at least recommended to run ASSP 2.4.3 (14313) ...
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75 views

viewing firewalld logs via remote login to CentOS 7 server

I have firewalld installed in a remote CentOS server. When I log into the server over the internet as root, I type the following command to access the firewalld logs: journalctl ...
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139 views

Network firewall on CentOS, host cannot be resolved?

I have a centos machine and I am trying install some dependencies using yum. When I do this I keep getting a message saying the host cannot be resolved. I was told the previous person that used the ...
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38 views

Application specific DNS problem?

I'm working on a live stream transcoder application using nginx + ffmpeg. Everything works fine when I use avconv to transcode, but if I use ffmpeg, I get this error: [tcp @ 0xb4e9da0] Failed to ...
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60 views

Allow wifi connections only to a local service, don't route to the wired ethernet

I have a Raspberry Pi running Linux (Raspbian) which is connected to my corporate Internet over an Ethernet cable. The RPi also has a wifi adaptor plugged into a USB port. I've been following along ...
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203 views

log files in CentOS 7 [closed]

In CentOS 7, how can I locate and view all the system logs that tell me who tried to enter the system, who got in, what processes they contacted, what they accomplished, etc. I want to be able to ...
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2answers
113 views

outgoing SMTP 25 port blocked by ISP?

I just setup postfix but I just realized my ISP outgoing blocks port 25 (SMTP). How do I send email outside? I can see my mail queue is filling up. Any suggestion?
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iptables: can't open tcp port

I'm running a Raspberry PI B+: Linux pi 3.12.28+ #709 PREEMPT Mon Sep 8 15:28:00 BST 2014 armv6l GNU/Linux The Raspberry is connect via lan (dhcp. ip: 192.168.78.29) to the local network. I'm trying ...
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44 views

Port randomly closing (iptables)

I'm running CentOS 6.5 on a VPS and one of the services I have running is murmur/mumble (A voip application). The issue I'm having is that the port clients connect on will be open when I initially ...
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Linux firewall techniques: MySql-Account

I'm having a discussion with a software developer in my nears. He is using MySql direct connections for a software. There is no PHP/SSH/whatever-Bridge involved for the communication, neither at ...
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Dovecot/Postfix mail server replies to [SYN] with [RST, ACK] when user attempts to connect (POP3). Likely iptables?

Currently I'm trying to troubleshoot an e-mail server that will allow users to send e-mail, but not log in to the server (POP3) or receive e-mail using their Outlook clients. Previously this was ...
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iptables fowarding rules

I have an iptables rule in the FORWARD section that looks like this: 17 0 0 CONFIRMED tcp -- * * 0.0.0.0/0 172.16.30.240 tcp spt:587 dpt:587 ctorigdst ...
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OpenVPN and routing problem on OpenWRT

My home topology: router1 (192.168.1.1) - D-Link dsl2540u server with static IP available from Internet (ADSL via ppoe). 4 LAN ports. router2 (192.168.1.2) - D-Link DIR-300 with OpenWRT. Plays ...
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74 views

Isolate subnets on the same interface

I need to isolate Subnets on a linux machine CentOS that act as gateway. I have the following scenario. CentOS eth0 pub ip addres eth0.1 192.168.1.1 eth0.2 192.168.2.1 Now eth0.1 and eth0.2 can ...
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55 views

Allowing web server communication in Linux firewall

I have a unique situation. Let's say my webserver ( e.g. 10.0.0.2) is connected to eth0 of my firewall (gw 10.0.0.1). A local network (192.168.0.0/24) is also connected to eth1 (192.168.0.1/24) of my ...
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How to set up a stateful firewall on an am335x Starter Kit board?

In the past, I have used the following script to set up a stateful firewall (on a normal x64 Ubuntu machine) without issue: iptables -P INPUT DROP iptables -P FORWARD DROP iptables -N TCP iptables -N ...
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114 views

Iptables and --tcp-flags

If I have the following rule in the nat-table in the prerouting chain: 0 0 REDIRECT tcp -- eth5 any anywhere anywhere tcp flags:FIN,SYN,RST,ACK/SYN redir ports ...
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213 views

pf blocks all in/out traffic instead of just the one port I wanted to block

I need to block one incoming port with pf. I'm new to pf, and I can't figure out what I'm doing wrong here. Here is my entire rule file, made to block incoming port 22: set block-policy drop pass in ...
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48 views

Securing NFS in a multihomed environment

In a virtualised environment (VirtualBox with host-only networking) I want to share a folder on the host with the guest via NFS. I think that to achieve this, I should bind the NFS listening port to ...
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Are there any loopholes in IP restricting sshd?

Say that i want to only allow username/password logins on my private network, but restrict all external sources on to key/cert login. I would do something like this: RSAAuthentication yes ...
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1answer
150 views

Why doesn't Postfix reject a specific client's connection attempts?

My SMTP server is being probed. It looks like a brute force attach on SASL, where they're going through a password dictionary. Having seen thousands of these lines in the log files Sep 18 14:09:52 ...
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Does -o and -i make sense when the target host is already connected to the interface specified?

iptables -A FORWARD -s 192.168.20.7 -d 10.10.48.3 -p tcp --dport 25 -o eth1 -j ACCEPT iptables -A FORWARD -s 10.10.48.3 -d 192.168.20.7 -p tcp --sport 25 -i eth1 -j ACCEPT Tuning the firewall of my ...
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How to disable domain service at port 53 on WAN side in OpenWRT?

nmap on the WAN IP shows PORT STATE SERVICE 53/tcp open domain after basic configuration on a fresh OpenWRT (version Chaos Calmer) system. But the service should not be visible from WAN, but ...
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Why doesn't ufw enforce firewall rules for traffic coming from Virtualbox VM

I've been running Linux Mint 17 on my laptop for a while and thought I had it locked down to not allow any incoming traffic through "Firewall Configuration" (ufw GUI)—I have also validated this from ...
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psad: do not block access to HTTP

I want to block intruders via psad, but HTTP and HTTPS should not be blocked. For example, if someone is scanning my dedicated server via nmap, psad should block him for 2 hours, but he should still ...
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204 views

Configure firewalld for OpenVPN (server-bridge) in Fedora 20

I've installed an OpenVPN server on Fedora 20 (server-bridge), but I cannot get it to work. I'm almost sure that It's a firewall issue. I'm trying to connect from an OSX client, but I can connect ...
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2k views

Redhat / Centos 7 Firewalld best practice for pptp or L2TP/IPsec rules

Having a quick look at Centos 7, and though I'd spin up a VPN daemon or 3, but immediately discovered the usual packages aren't yet in the core repositories, so had to dig around and found the ...
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curl timeout troubleshooting

I tried to curl popular websites e.g. curl google.com or curl google.com:80 and there is always a timeout error. Some troubleshooting steps performed: Able to curl localhost with response Able to ...