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Linux Netfilter Tutorials

Tutorials, howtos and tips about Linux netfilter/iptables firewall includes examples, configurations, blocking traffic and IP address, opening and closing ports, and much more. ( rss feed )

Apache IPv6 Configuration: Dual Stacked IPv4 & IPv6 Virtual Hosts

How do I configure Apache IPv6 networking under a UNIX / Linux / BSD operating system? How do I configure httpd IPv6 and IPv4 under a RHEL / CentOS / Fedora / Debian / Ubuntu Linux?
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DenyHosts: Remove / Delete an IP address

I‘ve followed your guide and installed denyhosts to protect on my RedHat 5.3 OpenSSH based server. However, I’ve been accidentally blocked out from my home ADSL IP address. I tried removing my blocked IP from /etc/hosts.deny, but it did blocked it again quickly. It appears that DenyHosts keeps track of the attempts somewhere on disk or memory. How do I remove my own home IP address from DenyHosts?
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Linux Iptables Open LDAP Server TCP Ports 389 and 636

The default Iptables configuration under CentOS / Red Hat / RHEL / Fedora Linux does not allow inbound access to LDAP service. How do I update iptables settings to allow access to the LDAP primary TCP #389 and encrypted-only TCP # 636 ports, while keeping all other ports on the server in their default protected state?
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Snmpd Listen to Specific IP Address ( BIND To Selected Interfaces )

How do I force SNMP (Simple Network Management Protocol) network management software to listen on public interfaces under RHEL / RedHat / Fedora / CentOS Linux server?
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Iptables Open VNC Port To Allow Incoming VNC Connections

How do I configure Linux system firewall to allow incoming VNC connections?
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Configure Linux As Bastion Host

What is bastion host? How do I configure bastion host under Linux? How do I create a firewall for a bastion host under any Linux distribution?
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Ubuntu Linux Save / Restore Iptables Rules

I want to make changes to an iptables configuration. How to do I Save and Restore an iptables Configuration in Ubuntu Linux server?
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Ubuntu Linux Add Static IPv6 Address Network Configuration

How do I configure static IPv6 networking under Ubuntu Linux server operating systems? How to enable IPv6 for Ubuntu Linux version 14.04 or 16.04 LTS server?
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Tunneling X Connection Through Intermediate Linux / BSD Gateway

I‘ve ssh gateway behind my NAT firewall. So all users must first login to my gateway host from the internet and then login to other machines on the LAN. This works great for cli based apps. However, few users would like to run x apps from internal LAN hosts and tunnel X display through intermediate ssh gateway and display back output on their local system. For example, from localsystem user makes connection as follows:

ssh -X user@gateway.example.com
ssh -X user@somelan.example.com

X forwarding fails with an error:

Error: Can’t open display:

How do I fix this problem and allow users to use X apps with my intermediate Linux / BSD gateway?
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Linux: Iptables Forward Multiple Ports

How do I forward multiple ports using Linux iptables based firewall?
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