firewall HowTo - Linux / Unix Q & A from nixCraft

HowTo: Linux Limit A Specific User’s Shell Account Network Bandwidth Using Bash Shell and Trickle

last updated September 18, 2015 in BASH Shell, Linux, Networking, UNIX

I am using a bash shell under Ubuntu Linux operating system. Sometime I need to restrict my own Internet bandwidth for all my shell applications such as ftp, sftp, wget, curl and friends. How do I limit the network speed under bash without setting up a complicated firewall and tc rules as described here?

Verify: Keepalived IP Failover Working Or Not With tcpdump Command

last updated July 1, 2010 in Networking

I‘ve installed keepalived IP failover software as described here. But how do I verify it is working or not?

BSD PF Firewall Block FTP Bruteforce Attacks

last updated August 13, 2009 in Anti Spam, FreeBSD, Networking, OpenBSD, PF Firewall, Security, UNIX

I see lots of failed FTP login attempts in my log file. How do I stop FTP bruteforce attack? What should I do to solve this problem under FreeBSD 7.x server operating systems?

FreeBSD / OpeBSD Running in KVM Does Not Accept FTP Traffic

last updated May 6, 2017 in Linux KVM

I‘ve setup FreeBSD and OpenBSD under KVM. Everything works great except ftp protocol. I’ve no firewall installed inside FreeBSD and OpenBSD. How do I configure Linux host KVM firewall to allow ftp traffic?

Reset PF Firewall Automatically While Testing Configuration With Remote Server Over SSH Session

last updated April 11, 2014 in FreeBSD, Networking, OpenBSD, PF Firewall, Security, UNIX

I would like to tell my BSD based PF firewall to flush out the current configuration every 2 minutes. This will help me, when I’m testing a new rules and configuration options. Some time I find myself locked out of my own remote server. How do I reset PF firewall automatically without issuing hard reboot?

FreeBSD Jail Access Private Network Via NAT and PF

last updated May 6, 2017 in FreeBSD, FreeBSD Jails (VPS), PF Firewall

I‘ve FreeBSD 7.x server with 3 jails are configured to run a mail, web and MySQL services. My FreeBSD box has two network interfaces. First, interface is connected to LAN and other is directly connected to the Internet via public IP. My DNS servers are hosted on private network (LAN). FreeBSD 7.x jail only support one interface and one IP address. How do I configure jail (FreeBSD vps) to access my DNS servers hosted inside my LAN using PF firewall?

Iptables: Unblock / Delete an IP Address Listed in IPtables Tables

last updated February 15, 2011 in BASH Shell, CentOS, Debian / Ubuntu, Iptables, Linux, Security, Suse, Troubleshooting, Ubuntu Linux

Q. I am a brand new user of a Linux iptables and I can’t find how to instruct my iptables to delete or unblock an IP address listed in iptables firewall. I’m using Debian Linux version. Can you help please?