leblanc
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ipv4 packet structure
I heard that the ipv4 header range from 20 to 60 bytes. I google around but could not validate that fact. Any ideas?
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Okay.
"60 bytes": No.
"Length—A 4-bit field containing the length of the IP header in 32-bit increments. The minimum length of an IP header is 20 bytes, or five 32-bit increments. The maximum length of an IP header is 24 bytes, or six 32-bit increments. Therefore, the header length field should contain either 5 or 6."
< http://www.ciscopress.com/articles/article.asp?p=348253&seqNum=4 >
"60 bytes": No.
"Length—A 4-bit field containing the length of the IP header in 32-bit increments. The minimum length of an IP header is 20 bytes, or five 32-bit increments. The maximum length of an IP header is 24 bytes, or six 32-bit increments. Therefore, the header length field should contain either 5 or 6."
< http://www.ciscopress.com/articles/article.asp?p=348253&seqNum=4 >
ASKER
Now I am confused. Can somebody explain the explanation below:
"
Internet Header Length (IHL)
The second field (4 bits) is the Internet Header Length (IHL), which is the number of 32-bit words in the header. Since an IPv4 header may contain a variable number of options, this field specifies the size of the header (this also coincides with the offset to the data). The minimum value for this field is 5 (RFC 791), which is a length of 5×32 = 160 bits = 20 bytes. Being a 4-bit value, the maximum length is 15 words (15×32 bits) or 480 bits = 60 bytes. "
http://en.wikipedia.org/wiki/IPv4#Packet_structure
"
Internet Header Length (IHL)
The second field (4 bits) is the Internet Header Length (IHL), which is the number of 32-bit words in the header. Since an IPv4 header may contain a variable number of options, this field specifies the size of the header (this also coincides with the offset to the data). The minimum value for this field is 5 (RFC 791), which is a length of 5×32 = 160 bits = 20 bytes. Being a 4-bit value, the maximum length is 15 words (15×32 bits) or 480 bits = 60 bytes. "
http://en.wikipedia.org/wiki/IPv4#Packet_structure
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