(usagi-users 03692) Re: Router Alert Query

[Remi Denis-Courmont <rdenis@xxxxxxxxxxxxxxxx>]

Selon Gayatri Bulla <gayatri.bulla@xxxxxxxxx>:

> I have a query related to Router Alert Option.
> In ip6_ra_control() function in ipv6_sockglue.c file, you are checking
> this:
>
> if (sk->type != SOCK_RAW || sk->num != IPPROTO_RAW)
>   return -EINVAL;
>
> I dint get the importance of sk->num != IPPROTO_RAW check.....
> Why are you checking the local port to be IPPROTO_RAW, what i feel is it
> should parse and handle all raw packets and not just IPPROTO_RAW packets.

It's not the port number, it's the socket protocol. If the protocol is not
raw, the application expects the layer 4 header (and upper layer payloads),
so there is no way it could receive a router alert option (which lies between
the IPv6 header and the actual layer 4 header) within the received data...

If you want to see Router Alert on non-IPPROTO_RAW sockets, I guess the
correct way consists of enabling the HOPOPTS socket option and use recvmsg(),
but then, you will receive all packets, not just the ones with Router Alert.

-- 
Remi Denis-Courmont
http://www.simphalempin.com/home/