> Infact i have never seen a single switch blade with more than 48 ports
> but even that is beside the point. The point really is the desiugn
I had a cisco with two FrameRelay 'ports' on it. I added 200 PVC
'devices' to the cisco setup. Last time I'll mention it, so remember it!
> I will argue that you _can not_ write a generic search algorithm for all
> these protocols. Unfortunately if you enforce one then the device search
> algorithm will have to be the same across the board.
I see no need to even have a generic search algorithm, each protocol
(ATM, FR, VLAN) can do whatever makes the most sense for it.
> It goes without any arguement that we have a very good worst case estimate
> today, given the practical limits. You try adding all those thousands of
> VLANs as devices and i can _guarantee you_ that you are not optimizing for
> the common case.
Ok, the question is where is the lookup 'hit' you are talking about.
Where is this searching that is slowing everything down? Don't just
say there is a hit, show me the specific code or logic where this hit takes
For incomming pkts, the packet is detected in eth.c, as it comes off
of the hardware. I can immediately hash to find the VLAN device.
Constant time, worst case, O(n), where n is the number of physical ethernet
ports, and this is only when configured to allow 4096 VLANs PER Ethernet device,
which is fairly non-standard.
After that, the packet goes on up the stack, as if it were from any other
So, I see no performance hit going up the stack, regardless of how many
devices you have...
Now, going down the stack, I know less about. However, it's something like:
send on a socket, which then looks at the routing to determine the interface
then send it out that device. Where is the lookup/search problem here? Surely
IP stack is not so dumb that it must do a linear search on the net_device
That would blow your performance to hell even if you only have 5-10 interfaces.
So, please either provide some concrete examples where having more devices
hurt performance, or quit arguing about it.
> I like Lennert and Gleb's because they dont use devices for the
> abstraction rather they attach themselves to the device. You dont.
I'm not sure you are correct here, Gleb, Lennert? Either way, my VLANs
are **logically** attached to devices, even if they don't have pointers
linked off of the ethernet device.
> You could use the aliasing interface if you wanted to add extra IP
> addresses (one per VLAN).
Maybe I want to add 20 IP aliases to a VLAN?
> I dont understand the DHCP problem. What has an app got to do with
> what happens at layer 2?
I do, DHCP uses packet filters and uses hard-coded offsets into the
raw packet. The 4 extra bytes throw it off by 4, and so it never things
it gets a packet on the right port. See the patch on my web site if you
want to learn more.
Ben Greear (greearb@xxxxxxxxxxxxxxx) http://www.candelatech.com
Author of ScryMUD: scry.wanfear.com 4444 (Released under GPL)