Appendix G. RFC Excerpts

Chapter 13 refers to specific TCP/IP headers that are documented here. This is not an exhaustive list of headers; only the headers used in the troubleshooting examples in Chapter 13 are covered:

  • IP Datagram Header, as defined in RFC 791, Internet Protocol

  • TCP Segment Header, as defined in RFC 793, Transmission Control Protocol

  • ICMP Parameter Problem Message Header, as defined in RFC 792, Internet Control Message Protocol

Each header is presented using an excerpt from the RFC that defines the header. These are not exact quotes; the excerpts have been slightly edited to better fit this text. However, the importance of using primary sources for troubleshooting protocol problems is still emphasized. These headers are provided here to help you follow the examples in Chapter 13. For real troubleshooting, use the real RFCs. You can obtain your own copies of the RFCs by following the instructions at the end of this appendix.

IP Datagram Header

This description is taken from pages 11 to 15 of RFC 791, Internet Protocol.

Internet Header Format 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |Version| IHL |Type of Service| Total Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Identification |Flags| Fragment Offset | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Time to Live | Protocol | Header Checksum | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ...

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