CCNA 3 Labs and Study Guide - BINARYBB.INFO – @jagalbraith

Protocol Value Network Layer Protocol
1 ICMP
6 TCP
17 UDP
88 IGRP
89 OSPF
Instructor Note: Although ICMP is identified by the number 1, it is not an upper-layer protocol, but operates in the
network layer. An ICMP packet is encapsulated with an IP header.
Field J Header Checksum
This field is used to check the integrity of the bits in the header. Because each router decrements the TTL
field, this checksum must be recalculated at each hop on the way to the destination.
Field K Source Address
This field is the 32-bit IP address for the source of the packet.
Field L Destination Address
This field is the 32-bit IP address for the destination of the packet.
Field M Options
IP options can be a number of things. If the options in this field do not extend the full 32 bits of this sixth
32-bit word, then padding is added. The data must begin on a new 32-bit word boundary.
Field N Padding
If necessary, the source will add zeros to the end of the last 32-bit word in the packet header to ensure that
the header always ends on a 32-bit word.
Sources
Chapter 3: EIGRP and Troubleshooting Routing Protocols 193
Check student sources to see if they are legitimate. “RFC 791 Internet Protocol” should be listed. For the
sample answers here, the RFC was used as well as the Cisco Press title Routing TCP/IP, Volume 1, Second
Edition, pp. 7-16. The website http://www.networksorcery.com was also consulted.