[Outages-discussion] [outages] UK wide DSL broadband outages

[Paul Lettington]

On Fri, Oct 21 2011 08:10:02 -0500, Frank Bulk wrote:
> Why did a 15-minute outage cause subtended customers to be out for much
> longer than that?

Because BT's RADIUS servers which look at the realm of the login and route the
session to the correct ISP are unable to cope with the load of all the ADSL
users in the country continually reconnecting during an outage like this.

So when BT can't connect the end user to the ISP they accept the end user's
session themselves with a RFC1918 IP address for exactly an hour and not
connected to the internet, to stop them trying to log in.

In today's outage, even though connectivity from BT to the ISPs had returned
within 15 minutes, users who didn't reboot their routers or force a new login
were stuck on the holding sessions until the hour expired. Also the sudden load
of reconnections exactly an hour after the outage started meant that BT's
RADIUS servers still couldn't cope, and put most of the customers back on a
holding session for a second hour.

-- 
Paul.