packet checksum

[wezyap]

how is the packet checksum and packet header checksum calculated for the tcp handshake packets, what is the matematichal formula?

[Thorn]

how is the packet checksum and packet header checksum calculated for the tcp handshake packets, what is the matematichal formula?

Have you ever heard of Google?

[wezyap]

well....

well, what all those pages from that search tells me that the packets have a checksums inside them, but not how those is calculated... and seting the checksum to zero would make the reciver discard it, right?

[TheCotMan]

well, what all those pages from that search tells me that the packets have a checksums inside them, but not how those is calculated... and seting the checksum to zero would make the reciver discard it, right?

Like things that are Open "Standards" for the internet, there are usually documents that describe them.
TCP, IP, UDP, ICMP? questions about these? Check the RFC.

rfc793

[chop]
Checksum: 16 bits
The checksum field is the 16 bit one's complement of the one's complement sum of all 16 bit words in the header and text. If a segment contains an odd number of header and text octets to be checksummed, the last octet is padded on the right with zeros to form a 16 bit word for checksum purposes. The pad is not transmitted as part of the segment. While computing the checksum, the checksum field itself is replaced with zeros.
...[chop]

If the RFC does not answer the question you have about a given protocol, then there are books that are more verbose.

Be careful when following RFC. Newer RFC can obselete older ones, or alter definitions or enhance them.

[wezyap]

thanks

thanks for the information TheCotMan. I realy apprisiated it.

[wezyap]

books

have read the rfc793 document, and now I am thinking about buy some books on this subject, and I surfed amazon.com and found The Protocols (TCP/IP Illustrated, Volume 1) and The Implementation (TCP/IP Illustrated, Volume 2) , and I wondered if someone have read them and would recomand them? and if so why/why not? and witch one of them have the most in-depth information about this tread's subject (checksum in tcp/ip packets), and is they up to date?

[TheCotMan]

have read the rfc793 document, and now I am thinking about buy some books on this subject, and I surfed amazon.com and found The Protocols (TCP/IP Illustrated, Volume 1) and The Implementation (TCP/IP Illustrated, Volume 2) , and I wondered if someone have read them and would recomand them? and if so why/why not? and witch one of them have the most in-depth information about this tread's subject (checksum in tcp/ip packets), and is they up to date?

For IPv4, TCP/IP Illustrated Vol I is pretty good. Since there has been little change with TCP/IP, IPv4 (except for additions of other protocols over IP for routing, etc.) it is still a good book for IPv4.

There is disagreement on Volume 2. Some people criticize the suggested methods for implementing TCP/IP WRT embedded devices, and OS with optimization for [speed|memory|resources|whatever].

It has been a while since I looked at Vol 2 or Vol 3, but Vol 2 was good as food for thought the last time I looked at it. (6 or 7 years ago)

I bought Vol 2 to better guess fundamental assumptions made by at least one coder on implementing TCP/IP suite of protocols, and see if I could find security issues that might be shared by other implementors who used closed source models.

There are several books on IPv6, but I have not found one that met my search criteria for estimating "a good book."

I like the style of Stevens with TCP/IP Illustrated an his other books. I also like Djitskra's style of writing. I strongly dislike the writing style of Tannenbaum.

[wezyap]

thanks

thanks again TheCotMan, I trust your review and order them.

[TheCotMan]

thanks again TheCotMan, I trust your review and order them.

Go to a bookstore and randomly select a few pages from each volume, and see if you like the style before you buy it.

Maybe you won't like Steven's style.