Cisco Catalyst 2000 Configuration Handbook page 305

284 Cisco LAN Switching Configuration Handbook
Table B-2 Assigned ICMP Type Numbers, Codes, Descriptions, and Associated RFCs
Type Code
39
40
0
1
2
3
41 to 255
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.
0
Figure B-4 UDP Datagram Format Showing Port Fields
0
Hdr len
Figure B-5 TCP Segment Format Showing Port Fields
Name
SKIP
Photuris
Reserved
Unknown Security Parameters Index
Valid Security Parameters, but Authentication Failed
Valid Security Parameters, but Decryption Failed
Reserved
1
UDP source port
UDP message length
1
TCP source port
Acknowledgment number
Reserved Code bits
Checksum
Options (if necessary)
2
Data ...
2
Sequence number
Data
Data ...
Reference
3
UDP destination port
UDP checksum
3
TCP destination port
Window
Urgent pointer
Padding