2. Specify a suitable name for the service, for example MySQL
3. Now enter:
• Type: TCP
• Source: 0-65535
• Destination: 3306
4. Click OK
3.3.3. ICMP Services
Another type of custom service that can be created is an ICMP Service.
The Internet Control Message Protocol (ICMP) is a protocol that is integrated with IP for error
reporting and transmitting control information. For example, the ICMP Ping feature uses ICMP to
test Internet connectivity.
ICMP Types and Codes
ICMP messages are delivered in IP packets, and includes a Message Type that specifies the format
of the ICMP message and a Code that is used to further qualify the message. For example, the
message type Destination Unreachable uses the Code parameter to specify the exact reason for
the error.
Either all ICMP message types can be accepted by a service (there are 256 possible types) or it is
possible to filter the types.
Specifying Codes
If a type is selected then the codes for that type can be specified in the same way that port
numbers are specified. For example, if the Destination Unreachable type is selected with the
comma delimited code list 0,1,2,3 then this will filter Network unreachable, Host unreachable,
Protocol unreachable and Port unreachable.
When a message type is selected but no code values are given then all codes for that type is
assumed.
ICMP Message Types
The message types that can be selected are as follows:
Echo Request Sent by PING to a destination in order to check connectivity.
Destination Unreachable The source is told that a problem has occurred when
delivering a packet. There are codes from 0 to 5 for this type:
• Code 0: Net Unreachable
• Code 1: Host Unreachable
• Code 2: Protocol Unreachable
Chapter 3: Fundamentals
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