On Wed, 22 Feb 2006 09:42:49 +0100 Jørgen Hovland <jorgen@xxxxxxxxxx> wrote: > > ----- Original Message ----- > From: "Stephen Hemminger" <shemminger@xxxxxxxx> > > > > On Tue, 21 Feb 2006 21:50:00 +0100 > > Jørgen Hovland <jorgen@xxxxxxxxxx> wrote: > > > >> Hi > >> > >> Is there a way to either: > >> Find the real ifindex/ifname a mac-address is bound to > >> or > >> Find the real ifindex/ifname of an incoming packet > >> ? > >> > >> I am writing a dhcp server and need to know what real interface the dhcp > >> request packet came from. An acceptable solution would be to get the > >> interface by the mac-address, but that can be faked so I would rather get > >> the interface by knowing where the data actually came from. Data is IP, > >> UDP broadcast. > >> I _could_ use raw sockets. The problem is when I do that, the program is > >> using ~8% cpu on a 3.2ghz xeon64 just reading packets without doing > >> anything due to the amount of traffic passing through the box (~200mbit > >> and increasing) so that doesn't look like a good idea. > > > > Why should the app care. If forwarding database is working correctly, the > > source mac > > of the incoming packet will be in the list and any response to it will go > > out that interface. > > > > Well there is no guarantee that the source mac isn't faked. Additionally, > the hardware address of the dhcp client is put inside a dhcp-packet, which > also can be faked. So I am stuck with two hardware addresses that I am > suppposed to believe are correct but have no information about where I > originally received them from. > I can live with this (I guess all the other dhcp servers do that too), but I > can't find a way to map a hardware address to a physical interface when > using bridgemode. I need to know this because the dhcp server will be > limiting the amount of leases you can get per interface (eg max 5 ips per > interface). It will also be assigning static IP-addresses based on what > interface the dhcp packet came from. I will also be using iptables to only > permit the IP+MAC traffic to/from the real physical interface so if you > don't use dhcp at all times, the traffic won't be permitted. > > > > > >> brctl showmacs returns a list of port numbers, but they dont make much > >> sense to me. They do not seem to be in the same order I added the > >> interfaces? Is there a mapping here? > >> > >> Example, > >> jorgen@ams41:/$ /tmp/brctl showmacs test0 > >> port no mac addr is local? ageing timer > >> 2 00:04:e2:a8:3b:d7 no 0.24 > >> 1 00:08:a1:85:39:fd no 17.31 > >> 133 00:0d:88:a3:61:4a no 9.90 > >> 1 00:14:22:b0:cd:e0 yes 0.00 > >> 133 00:16:c7:f5:8f:e2 no 0.48 > >> > >> Port 133 is the 901'th interface (0x385) I added to bridge test0. What > >> does 133 point to? The ifindex of this physical interface is 912 (0x390) > >> (retrieved with SIOCGIFINDEX). > > > > Arbitrary index assigned by bridge for STP usage. Slots get reused as > > ports are deleted and added. > > So there is no way to get the physical interface from a mac address? You can read the forwarding database (see brctl sources for how). But the value can change as result of traffic.
