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 and physdev match confusion

I'd like to be able to prevent a network bridge from generating certain types of traffic from some of its interfaces. If I understand iptables correctly, packets generate by a device appear on the ...
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What ports are essential and should generally be allowed on a Linux system?

I'm running a desktop computer, but one with high threat risk. I've blocked all ports using a firewall except: HTTP, HTTPS, DNS, one port for torrent client. Do any common processes in distros ...
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How can I protect my computer when the only way to access the internet is though a compromised internet connection?

I access the network through a connection which is most likely compromised by a MITM attack. I can't do much about it. What steps should I take to lessen the influence of this attack. I'm especially ...
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196 views

cntlm: the request was denied

I have configured CNTLM server between users and Windows TMG firewall. CNTLM configured with "allow all" - no any ACL or something like it: Gateway yes # # Useful in Gateway mode to allow/restrict ...
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1answer
481 views

iptables Port Forwarding — no service with the port

I have setup a network as in the image below: Firewall (FW) running CentOS 6 has two physical interfaces with subinterfaces: eth0:2 — 10.100.1.78/25 eth0:3 — 10.100.1.79/25 eth3 — 192.168.0.21/24 ...
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How to Block SSH Brute Force via Iptables and How does it work?

I'm planning to add the following rules to iptables to stop ssh brute force attack which are common these days. -A INPUT -i eth0.103 -p tcp -m tcp --dport 4522 -m state --state NEW -m recent --set ...
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2answers
4k views

FTP and iptables. Connection fails but ports are open

I installed proftp on my machine. With iptables disabled I can connect to the machine, using ftp-client or telnet. With iptables connection fails - telnet says "Connection failed" # works telnet ...
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38 views

Unable to apt-get after editing firewall settings

I am currently testing out the Tomcat on apache from turnkey Linux and I am unable to run any apt-get commands. The problem started when I edited the firewall settings from the webmin. How can I get ...
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1answer
7k views

Fedora 19: can't disable the firewall

I've installed a server (WSO2 ESB) in my laptop. When I run it, going to the browser and typing the console address https://10.13.6.75:9443/carbon, it works normally, but if I try it on another ...
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1answer
5k views

Is it better to set -j REJECT or -j DROP in iptables?

There's an example of iptables rules on archlinux wiki: # Generated by iptables-save v1.4.18 on Sun Mar 17 14:21:12 2013 *filter :INPUT DROP [0:0] :FORWARD DROP [0:0] :OUTPUT ACCEPT [0:0] :TCP - ...
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1answer
898 views

Understanding the iptables rules created by FirewallD [closed]

I am having a hard time trying to figure out what the iptables rules generated by FirewallD say. Focusing on the "public" input zone, I have the following rules: *filter :INPUT ACCEPT [0:0] :FORWARD ...
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46 views

How to send packets coming from a second router on a particular port back to the router, using iptables not a route

I have a Linux server which runs a particular service listening on a single TCP port. The Linux server connects to the internet using a PPP connection and also acts as router for a local network using ...
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1answer
192 views

Does negative vs positive matching impact firewall performance?

I am curious if using negative vs. positive matching impacts the performance of the netfilter stack. e.g. is iptables -I INPUT -p tcp -s 192.168.0.0/16 -j DROP equivalent to iptables -I INPUT -p tcp ...
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63 views

Shorewall “ERROR: Ordinary users may not start the /etc/shorewall configuration” in Cygwin

I am using Cygwin on Windows 7 and I have installed Shorewall 4.5.21.5. When I try to start shorewall in Cygwin, it gives me error: $ shorewall start ERROR: Ordinary users may not start the ...
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1answer
266 views

nc both fails and succeeds

Platform: RHEL 5.10 netcat Version: 1.84-10.fc6 I was trying to figure out if my inability to ssh was TCP-level and usually I use nc for this. This time, however, I got something unexpected. ...
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1answer
346 views

No internet even with iptables ACCEPT all

I was trying to setup the firewall settings, and probably did something wrong. I don't have internet now unless I stop iptables service I tried flushing,and accepting everything sudo iptables -F ...
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1answer
831 views

iptables couldn't load target allow

I am using the command below to allow all traffic from hosts on my internal network but it says "iptables v1.4.18: Couldn't load target `ALLOW':No such file or directory". What is the problem here? ...
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1answer
505 views

Archlinux not configured with iptables

I have been trying to set up iptables on my archlinux server, however when I run iptables -nvL I receive the error iptables v1.4.20: can't initialize iptables table 'filter': Table does not exist ...
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1answer
206 views

How do you do NAT port redirection with PF?

In Linux, you can do NAT port redirection with a command like this: iptables -t nat -A PREROUTING -i eth0 -p tcp --dport 80 -j REDIRECT --to-port 8000 What is the equivalent with BSD's PF?
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1answer
331 views

iptables - why the stun, turn ports are not working to allow end points to access the server?

I have this iptables where all working except tcp/udp port 3478 and 5349. $ cat /etc/sysconfig/iptables # Generated by iptables-save v1.4.7 on Thu Nov 21 10:21:41 2013 *filter :FORWARD ACCEPT [0:0] ...
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2answers
642 views

Do I need a special firewall on a personal computer

I am relatively new to Linux and was wondering about security issues. Most people agree that a virus-scanner is not useful on a linux system, but what about a firewall? I am using Debian wheezy stable ...
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1answer
38 views

Ubuntu blocks access to services when not logged in

I'm not really sure what's going on here. I have the following: A fresh install of Ubuntu 12.04 LTS. Jira 6.1.2 installed as per instructions from Atlassian. Confluence 3.5.13 installed as per ...
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destination IP mangle table

I have machine with 2 interfaces: eth1 connected to internet (ip xx.xx.xx.xx) eth0 connected to my laptop (ip yy.yy.yy.yy) I add those lines to the firewall file in order to manage the bandwidth ...
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fail2ban log parsing too slow on Raspberry Pi - options?

I'm running fail2ban on a Raspberry Pi at 950MHz which I cannot overclock further. The Pi is occasionally subject to SYN floods on particular ports. I've set up iptables to throttle the rate of SYNs ...
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560 views

How does KVM set its own netfilter rules?

I've been poking around with KVM VM's on Centos 6.4 and after some hair pulling and copious amounts of trying to break my desk with my head due to not having an internet connection on my VM's, I found ...
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2answers
861 views

Open a port CentOS

I'm new in CentOS and I'm trying to create a little script in Python, something like: $ python -m SimpleHTTPServer If I try to access port 8000 in my web browser, I don't get access, however if I ...
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1answer
589 views

Rsync over ssh tunnel - using gateway server

Environment: ---------- ---------- /| ------------ | Work | | Gateway| | | | cluster | |Station |--------------------------------| ...
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1answer
48 views

Reach service on VM with private address

I have this configuration: source: https://www.lucidchart.com/publicSegments/view/5256a1e5-afb0-4c7a-96fa-35750a00527d/image.png Basically, I have to reach a service which is running on the virtual ...
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174 views

Firewall config prevents hibernate connecting to postgres in CentOS6.3

I have an operating environment in CentOS 6.3 that has tomcat7 and postgres9.2 installed. There is just one web application deployed in tomcat that tries to establish a connection from localhost to ...
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1answer
221 views

What are the pros and cons to editing iptables configuration file vs adding rules via the iptables command

I am working with a product on CentOS that occasionally needs to automatically add and remove rules from the iptables configuration. For example, during an update, we want to explicitly refuse ...
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1answer
493 views

how to investigate Firewall blocked outbound TCP

CentOS webserver with CSF (Config Server Firewall) running. Blocking all outbound / Inbound traffic except listed ports 80 81 22 21 etc. for web, mail & FTP services etc. I'm use to seeing heaps ...
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571 views

FreeBSD ipfw keepstate vs setup keep-state

A lot of examples where people are using keep-state with setup together. For example: ipfw add 1 allow tcp from any to me 22 setup keep-state Because of setup, this rule will allow only SYN ...
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11k views

UFW: Allow traffic only from a domain with dynamic IP address

I run a VPS which I would like to secure using UFW, allowing connections only to port 80. However, in order to be able to administer it remotely, I need to keep port 22 open and make it reachable from ...
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464 views

Isolate a hosts networking with iptables

I want to isolate a host on my home intranet using iptables on my linux router. So say for instance, I have a host that has the IP of 10.0.1.50 and I want it to be able to talk to the rest of the ...
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FreeBSD pf firewall, new connections severly delayed when nating

I have a newly setup fbsd 9.1 with pf, which itself doesn't experience any slowness when for example downloading a debian iso from my local debian repo (ftp.se.debian.org). Any machine behind it, ...
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Full network logging via linux firewall ( iptables )?

How truly enable full network logging via iptables? There is an option --log-prefix to add a tag to log entries. But the log entries don't show all complete packets. What a grand way to enable full ...
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1answer
486 views

IPtables : Limit number of new ssh connections per minute

I need to ensure on my server that maximum new ssh connections per minute are not more then 5. sudo /sbin/iptables -A INPUT -p tcp --syn --dport 22 -m connlimit --connlimit-above 5 -j REJECT Above ...
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915 views

openwrt firewall - block a set of ip addresses from internet access

I'm running OpenWRT Attitude Adjustment r33556 / LuCI Trunk (trunk+svn9325) on my WNDR3800. I would like to configure my firewall to: Only allow a specific range of IP addresses to access internet, ...
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1answer
169 views

Linux GUI to track connections made from/to this computer

Is there a GUI to track any socket connection sent to this computer and which program that initiates it? Also if possible track any incoming connection sent to this computer and which program that ...
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1answer
314 views

Intercept incoming TCP/IP packets on Linux and perform NAT

I want to make a decision of what computer is behind the firewall sending the packet. Imagine I have 2 PCs behind the firewall and I want to, based on (my algorithm), make a decision at the firewall ...
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1answer
2k views

Creating UFW rule to allow application to use dynamic ports

I am currently trying to get a Google Chromecast device to work through my Ubuntu 13.04 based computer. Currently, the Google Chrome extension shows "no devices found" as long as my UFW firewall is ...
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1k views

Missing iptables file on directory /etc/init.d/ (Fedora 17)

Is the iptables file in Fedora 17 moved from /etc/init.d/ to /etc/sysconfig/? I need do some patching to the iptables file to solve the firewall problem (Setting chains to policy ACCEPT: security raw ...
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2answers
435 views

PF and types of NAT(Network Address Translation)

As you know, at least 3 types of NAT are used. Of course i need to two types of them.DNAT and SNAT. DNAT : hiding server behind NAT, SNAT : hiding your client behind NAT. Question: I read a quick ...
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3answers
5k views

what is the required ports to be opened on the firewall?

Currently I'll be installing one AIX server behind a firewall, I just asked to open port 443 to use the SSH protocol to access this UNIX server. I already changed the default ssh port to be 443 ...
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how to list blocked connections events by the firewall?

So, I used firestarter that had logged blocked connections events with some useful details (but it is not being updated and I found somewhat unsafe as any moment we could click to deactivate the ...
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1k views

Looking to build a low powered linux based firewall

I am looking to build a low powered linux based firewall. I need a reliable piece of hardware that has two (2) LAN inputs and a built in wifi. Fanless and low power system. any recommendations? Any ...
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1answer
103 views

Is there any tools which can be used to make ports available from any firewall network?

I have been testing my application which has TCP/UDP ports for peer to peer with the help of server signalling commands for making communication, that works when I have Public IP or Lan IP and not ...
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226 views

what is `firewalld --nofork`

I carelessly killed the following process root 470 1 0 Jun06 ? 00:00:13 /usr/bin/python /usr/sbin/firewalld --nofork Is there any consequence from killing the process? Are there ...
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1answer
85 views

RapidIO packet filtering in Linux

I was wondering if there is support in Linux Kernel for RapidIO packets filtering, something similar to iptables, but based on RapidIO header?
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1answer
408 views

ufw firewall rules for security.debian.org

What is a practical way to manage a whitelist of firewall outgoing connection rules for http://security.debian.org (on a server that blocks all outgoing connections by default)? My understanding is ...