socket(,,protocol): when htons?

when do I need to call htons on the 3rd argument to socket()?
it appears that 0 is the most common argument,
but I often see examples like
socket(,,htons(ETH_P_ALL));
and
socket(,,IPPROTO_TCP);
so, what is the rule?
what CPP #define's can be passed to socket() as the protocol?
which ones need htons()?

the next question is, of course,
how portable the answer to the previous question is?
(i.e., what are the proper protocol argument to socket() on *BSD &c)

thanks!

--
Sam Steingold (http://www.podval.org/~sds) running w2k
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Sam Steingold wrote:

> when do I need to call htons on the 3rd argument to socket()?

Never. That third argument is almost never needed, and since they are predefined
in the OS specific headers the values should already be in the proper format.

> it appears that 0 is the most common argument,
> but I often see examples like
> socket(,,htons(ETH_P_ALL));
> and
> socket(,,IPPROTO_TCP);
> so, what is the rule?
> what CPP #define's can be passed to socket() as the protocol?
> which ones need htons()?
>
> the next question is, of course,
> how portable the answer to the previous question is?
> (i.e., what are the proper protocol argument to socket() on *BSD &c)

If you are only using the TCP/IP protocol and need full portability then only
use '0' for the third argument.

--
Phil Frisbie, Jr.
Hawk Software
http://www.hawksoft.com

> * Phil Frisbie, Jr. <(E-Mail Removed)> [2005-10-11 19:51:46 +0000]:
>
> Sam Steingold wrote:
>
>> when do I need to call htons on the 3rd argument to socket()?
>
> Never. That third argument is almost never needed, and since they are
> predefined in the OS specific headers the values should already be in
> the proper format.

then why does googling for htons(ETH_P_ALL) returns 847 pages?
mostly in this context:
socket(PF_PACKET, SOCK_RAW, htons(ETH_P_ALL));

>> it appears that 0 is the most common argument,
>> but I often see examples like
>> socket(,,htons(ETH_P_ALL));
>> and
>> socket(,,IPPROTO_TCP);
>> so, what is the rule?
>> what CPP #define's can be passed to socket() as the protocol?
>> which ones need htons()?
>> the next question is, of course,
>> how portable the answer to the previous question is?
>> (i.e., what are the proper protocol argument to socket() on *BSD &c)
>
> If you are only using the TCP/IP protocol and need full portability
> then only use '0' for the third argument.

what if I need UDP and need full portability?

thanks for your help!

--
Sam Steingold (http://www.podval.org/~sds) running w2k
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Sam Steingold wrote:

>>* Phil Frisbie, Jr. <(E-Mail Removed)> [2005-10-11 19:51:46 +0000]:
>>
>>Sam Steingold wrote:
>>
>>
>>>when do I need to call htons on the 3rd argument to socket()?
>>
>>Never. That third argument is almost never needed, and since they are
>>predefined in the OS specific headers the values should already be in
>>the proper format.
>
> then why does googling for htons(ETH_P_ALL) returns 847 pages?
> mostly in this context:
> socket(PF_PACKET, SOCK_RAW, htons(ETH_P_ALL));

OK, raw sockets is another story, and it it is not really a protocol.

>>>it appears that 0 is the most common argument,
>>>but I often see examples like
>>> socket(,,htons(ETH_P_ALL));
>>>and
>>> socket(,,IPPROTO_TCP);
>>>so, what is the rule?
>>>what CPP #define's can be passed to socket() as the protocol?
>>>which ones need htons()?
>>>the next question is, of course,
>>>how portable the answer to the previous question is?
>>>(i.e., what are the proper protocol argument to socket() on *BSD &c)
>>
>>If you are only using the TCP/IP protocol and need full portability
>>then only use '0' for the third argument.
>
> what if I need UDP and need full portability?

TCP/IP includes both TCP and UDP sockets. Just use '0'.

--
Phil Frisbie, Jr.
Hawk Software
http://www.hawksoft.com

> * Phil Frisbie, Jr. <(E-Mail Removed)> [2005-10-12 16:21:19 +0000]:
> Sam Steingold wrote:
>>>* Phil Frisbie, Jr. <(E-Mail Removed)> [2005-10-11 19:51:46 +0000]:
>>>Sam Steingold wrote:
>>>
>>>>when do I need to call htons on the 3rd argument to socket()?
>>>
>>>Never. That third argument is almost never needed, and since they are
>>>predefined in the OS specific headers the values should already be in
>>>the proper format.
>> then why does googling for htons(ETH_P_ALL) returns 847 pages?
>> mostly in this context:
>> socket(PF_PACKET, SOCK_RAW, htons(ETH_P_ALL));
>
> OK, raw sockets is another story, and it it is not really a protocol.

call it whatever you like :-)
when does the 3rd argument go through htons?
when the second argument is SOCK_RAW?

>>>>it appears that 0 is the most common argument,
>>>>but I often see examples like
>>>> socket(,,htons(ETH_P_ALL));
>>>>and
>>>> socket(,,IPPROTO_TCP);
>>>>so, what is the rule?
>>>>what CPP #define's can be passed to socket() as the protocol?
>>>>which ones need htons()?
>>>>the next question is, of course,
>>>>how portable the answer to the previous question is?
>>>>(i.e., what are the proper protocol argument to socket() on *BSD &c)
>>>
>>>If you are only using the TCP/IP protocol and need full portability
>>>then only use '0' for the third argument.
>> what if I need UDP and need full portability?
>
> TCP/IP includes both TCP and UDP sockets. Just use '0'.

this works (to get ICMP packets):
socket(AF_INET,SOCK_RAW,1)
this does not:
socket(AF_INET,SOCK_RAW,0)

Thanks.

--
Sam Steingold (http://www.podval.org/~sds) running w2k
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