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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Iptables restrict all, allow multiple specified users to destination port

This great answer tells me how to prohibit all users from connecting to remote host on specified (in this case 25) port, except one user: iptables -I OUTPUT -m owner ! --uid-owner postfix -m tcp -p ...
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1answer
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Outgoing firewall application similar to Little Snitch for Mac

Is there a Linux application similar to Little Snitch? Little Snitch is an outgoing firewall that temporarily blocks outgoing network requests until the user decides whether to allow the connection or ...
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preventing DoS attack in Apache webserver

This is the version of apache we're using - httpd-2.2.15-39.el6.centos.x86_64 We recently had our website down due to DoS attack and hence started exploring iptables, and how to use it to prevent DoS ...
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1answer
989 views

Corosync & Pacemaker IPTables Rules

When using Corosync with two rings via multi-cast addresses 226.94.1.1 (Port 5405) & 226.94.1.2 (Port 5406) what iptables rules are required to allow two nodes to communicate optimally without ...
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1answer
13 views

UFW app based filtering

is there any filtering in ufw which works sort-of like win firewall? basically allowing me not only to create ip/port/proto based rules, but also to bind such limitations to specific executables ...
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1answer
4k views

Installing pfSense firewall on an SSD

I was looking at creating a home firewall running pfSense (as I could not get IPCop to boot properly on my hardware). Doing a little research, however, I have some concerns with installing it onto an ...
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3answers
233 views

How to stop outbound ftp from being established. centos/ rhel

What is the method to block a machine from establishing connection to an outside ftp server. Both ftp and sftp. inet, iptables, shutdown service?
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2answers
46 views

Domain only for web server

I have a domain which I want to point to my server. But I don't want to allow other people to use this domain to reach the server, only specific ports on the server (web server, so port 80). So if ...
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1answer
56 views

How would I limit connections to certain services, to be only accesed via a connection coming from a sub-domains?

I have a personall machine running Ubuntu 14.04.4 LTS. I use it to host a Teamspeak and a Minecraft server and also a website. I am trying to make sub-domains to only point to the right services. So ...
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22 views

Iptables ports not open

I was set up iptables, I made some forward rules, but the ports are not open for remote acess for exemple. If I'm in the same network of firewall, the Forward rules work well. But if I try to access ...
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86 views

Which iptables chain does a new stream created by TEE go to?

Where do packets go after being created by the TEE target? I am working on mirroring some traffic that needs to go to multiple computers on my network. So what happens to both streams after using ...
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1answer
43 views

iptables configuration

I'm trying to setup iptables, the forward rules are workin fine, but the output rules are making problems. I Can't access internet from the hosts beheind the firewall neither the firewall server can ...
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WLAN with multiple unique users

Following use case: There are 6 holiday apartments which all use the same WLAN. After a preceding law case due to illegal downloads every apartment needs to be monitored for eventually following ...
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1answer
31 views

Block countries based on IP in firewall

I would like to restrict visibility of my server from outside my country. I am connecting to my personal server always from one or two countries. Is there a way to block all the IPs coming from all ...
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1answer
38 views

Shorewall 4-interface setup

I am trying to use shorewall on Arch to manage a setup with 2 local networks and 2 ISP connections. Ultimately I want traffic from local network 1 (192.168.1.0/24 interface enp5s0) to use ISP 1 (76. .....
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2answers
2k views

NAT and source IP filtering in PF, using OpenBSD >= 4.7

I just read a book about PF (The Book Of PF, No Starch), but there's one question not answered by it. If I have a gateway machine using two interfaces, $int_if and $ext_if, and I NAT the packages ...
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0answers
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Why “echo f” in the case of clearing conntrack table doesn't work on debian?

Many people don't clear the conntrack table when they want to reload their firewall rules. When you have some ESTABLISHED connections, all the sessions won't be affected when you add a rule that ...
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What are the most restrictive external firewall / DNS listening port settings I can have for my DNS server (internal clients only)

This question relates specifically to hardening the configuration of DNS, firewalls and at the limit, ntp. (not proxys, http access,vpn's or other services). This is about the externally-facing side ...
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1answer
46 views

Add route from internal network to external network

I am using a box running Arch as my router and firewall (with shorewall). Recently, I tried to add another network onto the system, which failed horribly. After putting everything back where it was ...
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1answer
573 views

How would I go about getting UPnP working on a Slackware server/firewall?

I'm a long time fan of Slackware and I've always had a machine serving as my main server/firewall with the latest version installed. I have it now but I'm struggling to find information on how to ...
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1answer
872 views

How does KVM set its own netfilter rules?

I've been poking around with KVM VM's on Centos 6.4 not having an internet connection on my VM's, I found something curious: Upon booting the machine, iptables has rules in the FORWARD chain to allow ...
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3answers
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iptables: allow certain ips and block all other connection

How do I allow certain ips and block all other connection in iptables?
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DD WRT restrict access but exclude subdomain

I know it's possible to restrict access to some websites in Access restrictions section. I'd like to know if it possible to exclude from restriction subdomain of a site. For example: http://...
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1answer
101 views

Advanced Policy Firewall: allow_hosts.rules doesn't work

I'm trying to open ports for Nimsoft. In allow_hosts.rules I opened ports for private network: tcp:in:d=48000_48020:s=10.0.0.0/8 tcp:out:d=48000_48020:d=10.0.0.0/8 During starting apf I see that ...
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1answer
29 views

iptables connection mark not balance

The following is my network topology: + + | | | | | | | +-----------...
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1answer
95 views

how to find out which chain in iptables in listing

Suppose I have the following two entries line of iptables: iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE iptables -A INPUT -s 192.168.1.0/24 -j DROP So, I have POSTROUTING and INPUT chains. ...
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1answer
395 views

pfsense: No more processes

Sometimes my pfsense (1.2.3-RELEASE) goes crazy: every nat rules go down the web interface reply me with many errors (Warning: shell_exec(): Unable to execute...) my ssh daemon refuse to open a new ...
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1answer
101 views

iptables rule explanation

I was looking to update iptables in our webserver which would prevent DoS attack to an extent. 1) Related to web traffic, below are the iptables rules i found. iptables -I INPUT -p tcp --dport 80 -...
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1answer
979 views

Opening port 80 but remain secure

I have a standard installation of Ubuntu 10.04, and have installed the LAMP stack so I can do some web development locally. On my router I have opened port 80 so I can develop with external services ...
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33 views

Unable to access http server when ufw is running, on Raspbian?

I have a Raspberry Pi running Raspbian, with Apache2 for the web server. Some recent change seems to have broken my ability to access my web server, when ufw is running. The server simply doesn't ...
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1answer
29 views

Understanding Iptables rules to prevent DDoS

Following IPTables rules exist on my system as some preventive measures against DDoS attacks -A INPUT -s 255.0.0.0/8 -j LOG --log-prefix "Spoofed source IP" -A INPUT -s 255.0.0.0/8 -j DROP -A INPUT -...
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Why fail2ban doesn't put some IP address in jail

This is several days ago, I observed some IP addresses was't banned by fail2ban, and continued to brute force attack on different port of ssh. This an extract of my logwatch: undef: 22 times a [...
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1answer
53 views

How do I make sure the iptables is closed?

I want to disable iptables completely. I followed the instruction like /etc/init.d/iptables close it said there No such file or directory [root@dataapp02 tmp]# service iptables stop Redirecting ...
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IPtables installation question

I am new to installing iptables and have an excellent book called "Linux Firewalls: Attack Detection and Response" by Michael Rash. I have a few questions before I begin. I want to make an ...
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2answers
80 views

Packet flow in a virtual bridge with two interfaces, centos 7

I am struggling to create a bridge firewall with iptables since I cannot find/catch packets flowing through a bridge with two interfaces in centos7. No ip addresses are configured on interfaces or the ...
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1answer
111 views

What ports need to be open on a firewall to access the internet?

Let's say as the example that I have a firewall that blocks ALL ports from all sources/destinations. What ports would I need to open to be able to successfully run: ping google.com ...and are ...
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47 views

Access to the internet from a firewalled server

I'm trying to set up a test Docker platform at work. I need pull images, but can't do so because the test server does not have direct internet access (firewalled). There is another server that can ...
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12 views

pcfl - Allow ssh for an specific IP

I'm working with pfctl on Mac OS X. Im trying to make a policy/anchor what blocks SSH for ALL ips, minus specific ip. I try this: pass in on fxp0 proto tcp from any to any port < 22 flags S/SA ...
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1answer
1k 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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3answers
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iptables: block all inbound traffic over a certain port number

It is possible using iptables (on Debian) to block all inbound connections for all the ports with a port number over (as an example) 16000. Like this (using 16000 as reference): The port 15999 is ...
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2answers
1k views

Socket Connection Refused (raspbian) but ports are open for connections

I'd like to establish a connection between my client and raspbian. Within my network, I can connect to my service at any time without any problems. Now I want to connect to my service via the ...
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1answer
158 views

ufw allow ssh - and then connection gets lost

I'm trying to set up a debian server in the cloud, over SSH. I log in using a key. After the initial startup I want to set UFW: apt-get install ufw ufw allow ssh ufw enable This is how I've done ...
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1answer
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What does the “Incoming” option refer to in ufw?

I am configuring a firewall on my Linux Mint 17.2 to maximize security, mainly to put my mind at rest that no one will be able to do anything malicious. In gufw, there are options for allowing or ...
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1answer
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connlimit counters start over after iptables restored

I have a connlimit rule in iptables that allow only 5 connection to port 80. iptables -A FORWARD -p tcp -m tcp --syn --dport 80 -m connlimit --connlimit-above 5 --connlimit-saddr -j DROP This ...
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2answers
4k views

iptables based redirect captive portal style

What is a iptables set of rules that will force hosts connected to a access point, that try to access any website (port 80 of any ip or hostname) to be redirected to another device on the network (...
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4answers
20k views

What prevents a machine from responding to pings?

I have a CentOS release 5.4 linux box on Amazon EC2 that I'm trying to set up to be monitored via Nagios. The machine is in the same security group as the nagios server, but it seems to be ...
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How to firewall qemu/kvm guest in host machine?

I have a qemu guest with following network topology: Internet <-> eth1.96[bridge]tap96 <-> eth0[guest] I need to allow access to guest machine only from one specific /24 network and I ...
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531 views

Block outgoing connections to certain IP using PF

Can someone give me a hint on how to setup a basic deny rule whenever any TCP request is sent to a specific IP address? I am using the PF packet filter. Any help?
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63 views

Iptables rules doesn't work as expected

I need to block access to my server from the outside of my private network. I need to allow pings from my server out only to my private network and answer pings initiated from my private network as ...
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How to block access to “private” host-only network from VirtualBox nat interface (separate host-only networks)?

Scenario: 1 VirtualBox host with many vms. Different host-only networks are configured for different vm categories: Some vms are "private", others are "standard" vms. Most of these vms, including some ...