SWITCHlan Trouble Tickets

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Ticket 20200305_1

Ticket Number: 20200305_1Ticket State: CLOSED
Ticket Opened: 2020-03-05 11:58Ticket Closed: 2020-03-09 10:12
Ticket Description: IPv4 Routing issues to CloudFlare

Problem Description:

Several sites have reported issues reaching the DNS servers of
Cloudflare, a very large Content Distribution Network; this caused
problems for users trying to use the many Web sites there.

It seems that the major ISP of Madagascar has "leaked" some IPv4
routes to CenturyLink (formerly Level 3), which is one of SWITCH's
transit providers. Since we connect to CenturyLink in Geneva, the
problems mostly concerned customers in the Western part of

Also, customers with IPv6-enabled DNS servers were probably
unaffected, because the issue concerned IPv4 only, and only/mostly
routing the Cloudflare's name servers.


From 2020-03-05 10:30 until 2020-03-05 11:27
Impact: partial loss of connectivity
Service: network access


2020-03-09 10:22
Updated impact, in particular the start time.

Updated description with more precise description of impact extent.

2020-03-05 15:08
The situation has been stable since we adjusted the route filters to
avoid the problematic paths. We will discuss internally how to
minimize the impact of such route leaks on customer traffic in the

2020-03-05 11:27
We have adapted some route filters so that we use alternative
paths. Connectivity to all of Cloudflare should be as good as (or even
better than) usual from everywhere on the SWITCHlan backbone.

All times are in local Swiss time CET / CEST.
For all questions about this ticket, please send mail to noc@switch.ch
or call +41 44 268 15 30.