ia_netbroadcast

[Andre Oppermann]

Pawel Jakub Dawidek wrote:
> 
> Hi.
> 
> Do we still need ia_netboradcast field? It is calculated depending on
> old-fashion classes (A, B, C). Is it used still?
> I wonder if ia_broadaddr isn't sufficient today.

Yes, it should be sufficient and the ia_netbroadcast field doesn't serve
any special purpose anymore since it wrong most of the time anyway.  The
only problem you could run into is Windoze stuff.  They still use it
extensively and will broadcast their NetBIOS stuff always on the classful
netmask.  I don't know how much Samba and such depend on this.  You'll
have to check.

> IP              netmask         ia_broadaddr    ia_netbroadcast
> 10.0.0.101      255.0.0.0       10.255.255.255  10.255.255.255
> 1.0.0.2         255.255.255.252 1.0.0.3         1.255.255.255
> 2.0.0.1         255.255.0.0     2.0.255.255     2.255.255.255
> 
> I'm planing to work on removing O(n) from interface aliases search.
> Now every incoming packet have to be compared with every single
> broadcast from every single alias. When I tested something and
> there were ~10000 aliases on interface it worked really slow.

There are two ways I see to optimize this.  One is to use a hash for
the broadcast addresses too as with the IP address.  The second is to
go only into this loop if the packet was actually received on an
link level broadcast address (M_BCAST flag in mbuf packet header).
However this might work only for ieee802-type interfaces.

> This slowdown probably exists in more places. It exists in NetBSD and
> OpenBSD as well.

-- 
Andre


[patch to netinet/ip_fastfwd.c but same to ip_input.c]

        /*
         * Or is it for a local IP broadcast address on this host?
         */
        if ((m->m_flags & M_BCAST) &&
            (m->m_pkthdr.rcvif->if_flags & IFF_BROADCAST)) {
                TAILQ_FOREACH(ifa, &m->m_pkthdr.rcvif->if_addrhead, ifa_link) {
                        if (ifa->ifa_addr->sa_family != AF_INET)
                                continue;
                        ia = ifatoia(ifa);
                        if (ia->ia_netbroadcast.s_addr == ip->ip_dst.s_addr)
                                return 0;
                        if (satosin(&ia->ia_broadaddr)->sin_addr.s_addr ==
                            ip->ip_dst.s_addr)
                                return 0;
                }
        }