[asterisk-dev] Asterisk scalability

[John Todd]

On Feb 20, 2009, at 12:00 PM, Kevin P. Fleming wrote:

> John Todd wrote:
>
>> Hypothetical: My big router receives a 10gpbs ethernet from "the
>> Internet".  Then, that router has three 1gbps interfaces that feed
>> into my Asterisk box (which has three NICs.)  Thus, all of the  
>> traffic
>> appears to come from the MAC address on the distant side of the  
>> 10gbps
>> link.  I could generate the traffic from a zillion different
>> endpoints, so hopefully UDP port hashing would work.  Would this work
>> appropriately for spreading load on 802.3ad?
>
> If your 'big router' has three NICs connected to you, it will have  
> three
> MAC addresses for those NICs, and that's what you will see on your
> incoming packets, not the MAC address of the router on the other side.
>
> If your 'big router' is actually a switch (which I think is what you
> really meant), then your logic is correct.


I had assumed we were talking about seeing MAC addresses from the  
perspective of the device doing the load sharing on packets that were  
inbound from the Internet towards the Asterisk server.  That is the  
device that would have to "share" those packets across the three NICs  
of the Asterisk server, and therefore would have to come up with some  
algorithm to distribute evenly (or at least predictably) the traffic  
to the three interfaces.  Return traffic from the Asterisk server to  
the router/switch is the problem of the Asterisk box, but it looks  
like there are lots of knobs to turn on on the open-source side of the  
world with 802.3ad implementations that make that possible.

However, I'm speaking out of turn.  If others here think that 802.3ad  
works well and can "share" load across multiple NICs that are on a  
single host (versus just doing failover) then I'll believe them, but I  
haven't heard a "Yes absolutely it can be done" reply.  I strongly  
suspect that it does in fact work, but I've just never set it up to  
learn about the devil in the details.  It seems like 802.3ad would be  
a good way to share load across multiple NICs to reduce IRQ contention  
on the PCI backplane with high packet counts, and it also seems pretty  
universally supported by most mid-to-high end router/switch gear as  
well as Linux/BSD kernels.  It has the added benefit of reducing some  
single wiring points of failure, but introduces complexity.

Who has tried it?  Speak up!  Your experiences make you the one-eyed  
man in this land of the blind.

JT


---
John Todd                       email:jtodd at digium.com
Digium, Inc. | Asterisk Open Source Community Director
445 Jan Davis Drive NW -  Huntsville AL 35806  -   USA
direct: +1-256-428-6083         http://www.digium.com/