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ping request

Simple Linux and UNIX Shell Script Based System Monitoring With ping Command

You can simply monitor your remote system hosted in some remote IDC. There may be many reasons for which system may out of the network. This simple script is useful to monitor your own small network at home or work.
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Linux Iptables allow or block ICMP ping request

The Internet Control Message Protocol (ICMP) has many messages that are identified by a “type” field. You need to use 0 and 8 ICMP code types.

=> Zero (0) is for echo-reply

=> Eight (8) is for echo-request.

To enable ICMP ping incoming client request use following iptables rule (you need to add following rules to script).

My default firewall policy is blocking everything.

Task: Enable or allow ICMP ping incoming client request

Rule to enable ICMP ping incoming client request ( assuming that default iptables policy is to drop all INPUT and OUTPUT packets)

SERVER_IP="202.54.10.20"
iptables -A INPUT -p icmp --icmp-type 8 -s 0/0 -d $SERVER_IP -m state --state NEW,ESTABLISHED,RELATED -j ACCEPT
iptables -A OUTPUT -p icmp --icmp-type 0 -s $SERVER_IP -d 0/0 -m state --state ESTABLISHED,RELATED -j ACCEPT

Task: Allow or enable outgoing ping request

To enable ICMP ping outgoing request use following iptables rule:

SERVER_IP="202.54.10.20"
iptables -A OUTPUT -p icmp --icmp-type 8 -s $SERVER_IP -d 0/0 -m state --state NEW,ESTABLISHED,RELATED -j ACCEPT
iptables -A INPUT -p icmp --icmp-type 0 -s 0/0 -d $SERVER_IP -m state --state ESTABLISHED,RELATED -j ACCEPT

How do I disable outgoing ICMP request?

Use the following rules:

iptables -A OUTPUT -p icmp --icmp-type echo-request -j DROP

OR

iptables -A OUTPUT -p icmp --icmp-type 8 -j DROP

ICMP echo-request type will be block by above rule.

See ICMP TYPE NUMBERS (type fields). You can also get list of ICMP types, just type following command at shell prompt:
# /sbin/iptables -p icmp -h

Linux Iptables: Block All Incoming Traffic But Allow SSH

This is very common scenario. You want to permit access to a remote machine only by SSH. You would like to block all incoming traffic to your system except ssh connection under Linux.
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