Re: A question about linux/net/ipv4/ipcomp.c

[Herbert Xu]

Igor V. Liferenko <[EMAIL PROTECTED]> wrote:
>
> Would you please say why it's 60, and not 52?

The header length / 4 must fit within a single hexadecimal
digit.  Therefore the maximum is 15 * 4 = 60.

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A question about linux/net/ipv4/ipcomp.c

[Igor V. Liferenko]

Hello, everyone.

I'm having fun reading RFC's and looking through linux source code for
implementation examples.

What I'm not able to understand is this piece of code :

union {
struct iphdriph;
charbuf[60];
} tmp_iph;

and corresponding RFC 791 statement : "The maximal internet header is
60 octets."

Would you please say why it's 60, and not 52?

Well, what I came up with is this :

RFC791: "The option-length octet counts the option-type octet and the
option-length octet as well as the option-data octets". [i.e.
options' total length may be up to 2^8/8 octets (32)]. Then, header
lenght without options is 20 octets. So, a maximum header length is
32+20=52 octets. RFC791: "Internet Header Length is the length of the
internet header in 32 bit words..." 52 octets is 52*8 bits and it's a
multiple of 32.

Thanks in advance
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