ICMP type 38, Domain Name reply
Description Glossary RFCs Publications Obsolete RFCs

Description:

Protocol suite: TCP/IP.
Protocol type:Transport layer control protocol.
Base protocol: ICMP, Internet Control Message Protocol.
Related ICMP message: Domain Name request.
Host implementation: Mandatory.
Router implementation:Mandatory.
Links: IANA: ICMP parameters.

RFC 1788, page 5:

The IP Source in a Reply MUST be the same as the IP Destination of the corresponding Request message.

MAC header IP header ICMP message 38

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 Code ICMP header checksum
Identifier Sequence number
Time-to-live
Names :::

Type. 8 bits. Set to 38.

Code. 8 bits. Set to 0.

ICMP Header Checksum. 16 bits.
The 16-bit one's complement of the one's complement sum of the ICMP message, starting with the ICMP Type field. When the checksum is computed, the checksum field should first be set to 0. When the data packet is transmitted, the checksum is computed and inserted into this field. When the data packet is received, the checksum is again computed and verified against the checksum field. If the two checksums do not match then an error has occurred.

Identifier. 16 bits.
Copied from the request.

Sequence number. 16 bits.
Copied from the request.

Time-to-Live. 32 bits, signed 2s complement.
The number of seconds that the name may be cached.

Names. Variable length.
Zero or more Fully Qualified Domain Names. The length of this field is determined from the total length of the datagram. When no names are known, the field is eliminated and the reply is sent as an authoritative indication that no name is known. When more than one name is known, all such names should be listed. Any name which cannot entirely fit within the Reply MTU is not sent in the reply.

Glossary:

RFCs:

[RFC 1788] ICMP Domain Name Messages.

Publications:

Obsolete RFCs:

Description Glossary RFCs Publications Obsolete RFCs