ICMP Address Mask Request

Address Mask Request is an ICMP query message, normally sent by a host to a router in order to obtain an appropriate subnet mask.

Message Format:

00

01

02

03

04

05

06

07

08

09

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

31

Type = 17

Code = 0

Header Checksum

Identifier

Sequence Number

Address Mask

• Type must be set to 17.
• Code must be set to 0.
• The Address Mask can be set to 0.

Recipients should reply to this message with an Address Mask Reply message.

ICMP Address Mask Request may be used as a part of reconnaissance attack to gather information on the target network, therefore ICMP Address Mask Reply is disabled by default on Cisco IOS [1].

See also

• ICMP Address Mask Reply

References

• RFC 950