Updated notice on Cisco and land.c

This is an update to the previous notice. I originally planned just to have
this updated on the Web site and to post a pointer to the updated Web page,
but the Web posting seems to be taking a really long time, and I don't want
to delay the notice any longer. This version will eventually (probably by the
time most of you read this) be posted at


That URL will be updated with future versions. We probably won't send the
whole text out again.

Important differences between this notice and the last one:

   o There are definitely versions of classis Cisco IOS software that are
     badly affected by the land.c attack.

   o The notice contains detailed information about which IOS versions are

   o Catalyst 5000s, and probably other Catalyst switches, are affected.

   o Various editing and advice changes... nothing really substantive.

        -- John B.


Field Notice:
TCP loopback DoS Attack (land.c) and Cisco Devices

November 22, 1997, 08:00 AM US/Pacific, Revision 2