284 Cisco LAN Switching Configuration Handbook
Table B-2 Assigned ICMP Type Numbers, Codes, Descriptions, and Associated RFCs
Type Code Name Reference
39 SKIP
40 Photuris
0Reserved
1 Unknown Security Parameters Index
2 Valid Security Parameters, but Authentication Failed
3 Valid Security Parameters, but Decryption Failed
41 to 255 Reserved
B-3: Well-known IP Port Numbers
Transport layer protocols identify higher-layer traffic with 16-bit fields called port num-
bers. A connection between two devices uses a source and a destination port, both con-
tained within the protocol data unit. The User Datagram Protocol (UDP) header format
is shown in Figure B-4 with the source and destination port fields shaded. The UDP
checksum is optional for IPv4. Figure B-5 shows Transmission Control Protocol (TCP)
header format with the source and destination port fields shaded.
0123
UDP source port UDP destination port
UDP message length UDP checksum
Data …
Figure B-4 UDP Datagram Format Showing Port Fields
0123
TCP source port TCP destination port
Sequence number
Acknowledgment number
Hdr len Reserved Code bits Window
Checksum Urgent pointer
Options (if necessary) Padding
Data
Data ...
Figure B-5 TCP Segment Format Showing Port Fields
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