Unless you have been using Firewalld in the last few releases of Fedora, as some out there have, then you probably could probably use a few pointers to get you started on your way to configuring your Linux firewalls the “new-fangled fancy way”. This is especially the case if you plan on moving to RHEL7 anytime soon — as Firewalld is the default there. So put on your big boy (or girl) pants and say goodbye to your old friend IPTABLES.
provides a dynamically managed firewall with support for network “zones” to assign a level of trust to a network and its associated connections and interfaces. It has support for
firewall settings. It supports Ethernet bridges and has a separation of runtime and permanent configuration options. It also has an interface for services or applications to add firewall rules directly”
Wow, how fancy. So how do we use it? Well let’s take a stab at enabling HTTP access to our Fedora21 workstation.
First thing first, lets figure out what our default done is on our workstation.
Rsyslog has replaced Syslog as the default logging daemon in RHEL6. Rsyslog was designed to complete with syslog-ng and has several enhancements over plain old syslog. This includes but is not limited to more granularity with timestamps, direct database logging, TCP support, and relay server names in host fields which makes it easier to track the path a message has taken.
Below we are going to take a look at a few simple rsyslog configuration items.
Configure Rsyslog to Accept Remote Logs.
Within /etc/rsyslog.conf, comment out either the TCP or UDP syslog reception lines below. TCP is more reliable, however UDP is more widely supported.
To send all messages of info priority or higher to a remote host via udp, use the following format. Note that 10.1.224.34 is the remote server that I want to send logs to.
To send the same priorities to the remote host via TCP, use two "@@"
Note that you can specify the port number on which to send by using IP:PORT. When no port is specified the default port of 514 is used.
Note that depending on your configuration you may need to alter your IPtables configuration on your sending and/or receiving server. In my case I needed to allow UDP on port 514 on my remote syslog server. To accomplish this I used system-config-firewall-tui which added the following line to /etc/sysconfig/iptables.
-A INPUT -m state –state NEW -m udp -p udp –dport 514 -j ACCEPT
Which shows up as what you see below in the output of 'iptables -L'
ACCEPT udp – anywhere anywhere state NEW udp dpt:syslog
Testing Your Configuration
Ok lets send a test to our remote syslog server. Note that rsyslog has been restarted on both hosts.
# logger "testing to remote rsyslog server"
Checking the messages file on the remote host we can see that the test message has arrived.
Aug 13 14:55:26 vfatmin02 root: testing to remote rsyslog server
Today on the fatmin we are going to setup an ftp server on RHEL6 that accepts anonymous uploads. We are going to do so with SELinux support and will be making modifications to iptables as well. Sounds fun, right?
First and formost we need to install vsftpd
# yum -y install vsftpd && service vsftpd start && chkconfig vsftpd on
Our anonymous upload directory will be /var/ftp/anon, and we need to change group ownership to the ftp group and then change permissions so that the members of that group can write to it. Note that no one other than root can read or execute anything under /var/ftp/anon.
Your mother and I were talking last night about how important it is to properly configure Iptables, and how despite that fact, many just choose to disable it. So today we are going to discuss iptables.
By far the easiest way to setup a simple firewall using Iptables is to use system-config-firewall, or system-config-firewall-tui. I prefer this method as iptables can be a bit confusing on the command line and in its config file (/etc/sysconfig/iptables) is not exactly user friendly. At the very least you can create a basic set of rules and then customize by hand. Lets take a look at the file in its default form on my RHEL 6 box.
But before we do that, lets review a couple of terms that we need to know.
INPUT – are inbound packets
OUTPUT are outbound packets
FORWARD – packets from another machine that the firewall should forward (like to a vm on the host).
ACCEPT – the packet is accepted
DROP – the packet is dropped as if it never existed
REJECT – the packed is rejected and and error message is returned to sender
RULE – the basic building block — tells the firewall what to do with a packet
CHAIN – a list of all rules which will be checked in order from first to last
POLICY – the default action, like accept, drip, reject, forward
Now that you have memorized the list above, here is my /etc/sysconfig/iptables.
# Firewall configuration written by system-config-firewall # Manual customization of this file is not recommended. *filter :INPUT ACCEPT [0:0] :FORWARD ACCEPT [0:0] :OUTPUT ACCEPT [0:0] -A INPUT -m state –state ESTABLISHED,RELATED -j ACCEPT -A INPUT -p icmp -j ACCEPT -A INPUT -i lo -j ACCEPT -A INPUT -m state –state NEW -m tcp -p tcp –dport 22 -j ACCEPT -A INPUT -j REJECT –reject-with icmp-host-prohibited -A FORWARD -j REJECT –reject-with icmp-host-prohibited.
Now lets run system-config-firewall tui and enable apache and ftp, plus we want to configure our box to respond to ICMP ping requests. This process is pretty self explanitory once you start.
Once that is done lets view /etc/sysconfig/iptables again.
# Firewall configuration written by system-config-firewall # Manual customization of this file is not recommended. *filter :INPUT ACCEPT [0:0] :FORWARD ACCEPT [0:0] :OUTPUT ACCEPT [0:0] -A INPUT -m state –state ESTABLISHED,RELATED -j ACCEPT -A INPUT -p icmp -m icmp –icmp-type echo-request -j REJECT –reject-with icmp-host-prohibited -A INPUT -p icmp -m icmp –icmp-type echo-reply -j REJECT –reject-with icmp-host-prohibited -A INPUT -p icmp -m icmp –icmp-type destination-unreachable -j REJECT –reject-with icmp-host-prohibited -A INPUT -p icmp -j ACCEPT -A INPUT -i lo -j ACCEPT -A INPUT -m state –state NEW -m tcp -p tcp –dport 22 -j ACCEPT -A INPUT -m state –state NEW -m tcp -p tcp –dport 80 -j ACCEPT -A INPUT -m state –state NEW -m tcp -p tcp –dport 21 -j ACCEPT -A INPUT -m state –state NEW -m tcp -p tcp –dport 443 -j ACCEPT -A INPUT -j REJECT –reject-with icmp-host-prohibited -A FORWARD -j REJECT –reject-with icmp-host-prohibited COMMIT
The iptables command can be used in several different ways.
List the current rules in use, similar to viewing the /etc/sysconfig/iptables file
To set a default policy use iptables -P, in the example below we are setting the default INPUT policy to DROP.
#iptables -P INPUT DROP
Now lets say we want to delete all our existing rules, note that i did not say policy
To add a rule use iptables -a, for example lets say you have a default policy of INPUT DROP but we want to accept all established and related packets. Note that -m must be used when adding rules to a chain as it forces modprobe to load any necessary modules.
#iptables -A INPUT -m state –state ESTABLISHED, RELATED
Now lets say that we want to reject all packets from 192.168.10.10. Note -j specifies the action that the rule is to take — in the case below, REJECT
#iptables -A INPUT -s 192.168.10.10 -j REJECT
Now lets say we want to ACCEPT all ICMP traffic from our local subnet. The -p is protocol
#iptables -A INPUT -p ICMP -s 192.168.1.0/24 -j ACCEPT
Please note that under RHEL you can use following commands to save firewall rules.Make sure that you do this before you restart iptables.
This post is the first in what I suspect will be a semi-long list of post-install hints and tips as I go through and start rebuilding my cluster as Vsphere 4. Hopefully I will learn a lot along the way… like for example the fact the ntp and snmp traffic is not allowed by default by the ESX Firewall.
But before we go there we first need to make sure that our services are starting at boot.
>chkconfig ntp on, … do the same for snmp
Then lets fix the firewall. First lets fix ntp.
esxcfg-firewall -e ntpClient
Then lets verify that all is well with…
esxcfg-firewall -q ntpClient
This command returns…
Service ntpClient is enabled
Ok now lets fix snmp using the same commands above, but specific for snmp.
esxcfg-firewall -e snmp and esxcfg-firewall -q snmpd.
While you are at it add the following to you snmp.conf