Vice

0Now ICMP error messages are themselves actually encapsulated in an IP datagram. It is a rather funky looking packet actually, and tends to be confusing to those just starting to learn about ICMP. Fear not though, for we will cover various types of ICMP error messages at the packet level. The first four bytes of an ICMP error message always have the same format. What follows though can vary as it is dependent upon the error condition being reported. That being said the ICMP echo request, echo reply packet is different as it relates to the header itself. The ping packet as ICMP echo request/echo are also known as, have a header size of eight bytes vice four. This is because other specific information is required. More on that ICMP quirk to follow later on. On that note let’s see the layout of the first four bytes that remain the same.02br
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101 byte 1 byte 2 bytes12br
11i10___________________12i12br
10| Type | Code |Checksum |12br
10-------------------------------- 12br
10So we can see that there are four bytes in an ICMP error message that remain constant. If you check the 15010 that I recommended you download, you will see a representation like the one above. Please remember that it is found under “Additional Resources” at the bottom of the page.12br
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11font10You should be an expert in networking or rather you should have some knowledge of networking to understand the above jargon. I don't expect everybody to know those things.11b10 I know these things as I work with them. 12b12font12br
10My sole question is on the following sentence.12br
11font10The ping packet as ICMP echo request/echo are also known as, have a header size of eight bytes vice four.12font12br
11b10What is 'vice four'? The word 'vice' is incongruous with the rest of the words. For me, simply, it has no meaning here. Do you have any idea?12b12br
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10[ I don't know much about IPv6. I know everything about IPv4.] 12br
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10 0230hrefhttp://www.sans.org/resources/cTCP/IP and tcpdump flyer