ICMP Operation (4 bytes)

Protocol: ICMP ICMP PCI

Field: operation

Length: 4 bytes

Contents: additional information referring to the ICMP code.

Some ICMP option type leave this field free; some other (e.g. 'parameter problem') will use it.

ICMP operation codes depending on ICMP type values:

TYPE = 0/8 - Echo Reply/Request

Bytes 1+2: Identifier

The source station transmits a process identifier which is returned by the receiving

Bytes 2+4: Sequence Number

The source station transmits sequence numbers being incremented from frame to frame; this sequence number is returned by the receiving station.

TYPE = 4 - Redirect

Bytes 1-4: Router Address

The next router's address that can reach the destination network.

TYPE = 12 - Parameter Problem

Byte 1: Pointer

The pointer indicates the problem type, e.g. (list not complete):

1 = error in the "Type of Service" field

20 = error in the "Type Code" of the first IP option

TYPE = 13/14 - Timestamp Request/Reply

Bytes 1+2: Identifier

The source station transmits a process identifier which is returned by the receiving station.

Bytes 3+4: Sequence Number

The source station transmits sequence numbers being incremented from frame to frame; this sequence number is returned by the receiving station.

TYPE = 15/16 - Information Request/Reply

Bytes 1+2: Identifier

The source station transmits a process identifier which is returned by the receiving station.

Bytes 3+4: Sequence Number

The source station transmits sequence numbers being incremented from frame to frame; this sequence number is returned by the receiving station.