----- Original Message -----
From: "Stephen Hemminger" <[EMAIL PROTECTED]>
On Tue, 21 Feb 2006 21:50:00 +0100
Jørgen Hovland <[EMAIL PROTECTED]> 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,
[EMAIL PROTECTED]:/$ /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? Is
there any way at all? Do you plan to add this functionality?
Would you accept a patch if I were to submit any (I can't guarantee anything
atm) ?
As an example, Cisco IOS support mac lookup just fine.
Secondly,
I seem to be unable to add more than around 1024 interfaces to a single
bridge. Is there a way to increase this limit?
Increase BR_PORT_BITS (you can go up to 15) but you will lose priority
bits on the spanning tree.
Also, why? You performance is going to start to fall off with so many
interfaces. Can't you
partition to multiple machines?
Perhaps it would be better to split it into multiple bridges. I was planning
on having 1 bridge per router, and one router will have ~3000 interfaces. I
will reconsider this. Thank you.
Joergen
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