[Bloat] came across an unexpected side-effect of bufferbloat

Bill Ver Steeg (versteb) versteb at cisco.com
Mon Aug 3 10:11:33 EDT 2015

It is even worse than that - On some really crappy low end devices, applications do not get a taste of the CPU if there is a packet to be sent. If there is always a packet to be sent, the SNMP daemon and/or some DOCSIS/DSL/FTTx tasks (and other application level tasks that need to interact with the control plane) don't run. Eventually something weird happens, like a memory leak or a dead-man timer and  the box reboots. Clearly, this is sub-optimal. 

Fortunately, Darwinian pressures have made this type of device less prevalent in the marketplace. You can still run into some really poor CPE in the wild, though.

Bill VerSteeg

-----Original Message-----
From: bloat-bounces at lists.bufferbloat.net [mailto:bloat-bounces at lists.bufferbloat.net] On Behalf Of Steinar H. Gunderson
Sent: Monday, August 03, 2015 10:01 AM
To: bloat at lists.bufferbloat.net
Subject: Re: [Bloat] came across an unexpected side-effect of bufferbloat

On Mon, Aug 03, 2015 at 11:53:40PM +1000, jb wrote:
> While researching a little I came across a message on the Amazon 
> support forums that said after 3 hours of uploading to Amazon, their 
> cable modem would crash and reboot. The reason was that the SNMP the 
> cable modem needed to stay healthy was timing out (due to the 
> excessive latency induced by the continuous uploading). The author didn't know it was bufferbloat, of course.

FWIW, you don't need bufferbloat for this to fail. A classic thing with switches (typically underbuffered rather than overbuffered!) is that when you run the links full, the OSPF packets get dropped and eventually your link flaps because the other side thinks you're down.

This is one of the reasons why most L3 switches (well, anything that's advanced enough to do OSPF or the likes in the first place :-) ) have QoS at
all: You need to protect your administrative traffic.

/* Steinar */
Homepage: http://www.sesse.net/
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