COMMAND
Cisco
SYSTEMS AFFECTED
Catalyst 5000 Series 802.1x
PROBLEM
Following is based on a Cisco Security Advisory. When an 802.1x
frame is received by an affected Catalyst 5000 series switch on a
STP blocked port it is forwarded in that VLAN instead of being
dropped. This causes a performance impacting 802.1x frames
network storm in that part of the network, which is made up of
the affected Catalyst 5000 series switches. This network storm
only subsides when the source of the 802.1x frames is removed or
one of the workarounds in the workaround section is applied.
This vulnerability can be exploited to produce a denial of service
(DoS) attack.
This vulnerability is described in Cisco bug id CSCdt62732.
Cisco Catalyst 5000 series switches based on any of the following
EARL (Encoded Address Recognition Logic) hardware revisions:
* EARL 1
* EARL 1+
* EARL 1++
and running any of the following switch software revisions:
* 4.5 (11) or earlier
* 5.5 (6) or earlier
* 6.1 (2) or earlier
are affected by this vulnerability. This series includes the
Catalyst models 5000, 5002, 5500, 5505, 5509, 2901, 2902 and 2926
switches. To determine your hardware and software revision type
sh mod on the console prompt of the switch.
When an 802.1x (IEEE standard for port based network access
control) frame is received by an affected Catalyst 5000 series
switch on a STP (Spanning Tree Protocol) blocked port it is
forwarded in that VLAN (Virtual Local Area Network) instead of
being dropped. This causes a performance impacting 802.1x frames
network storm in that part of the network, which is made up of
the affected Catalyst 5000 series switches. This network storm
only subsides when the source of the 802.1x frames is removed or
one of the workarounds in the workaround section is applied.
When an affected Catalyst 5000 series switch network receives an
802.1x frame it causes an 802.1x frames network storm. This
network storm degrades the performance of the network. Slower
ports on the affected Catalyst 5000 series switches may stop
passing user data. The affected Catalyst 5000 series switches
may not respond to any management inquiries via SNMP, Telnet or
HTTP. However, management via the console port on the switches
is still possible and can be used to apply the workarounds.
SOLUTION
Catalyst 5000 series switches based on EARL 2 or later hardware
revisions are not affected by this vulnerability. Catalyst 5000
series switches regardless of the EARL hardware revision, running
the following switch software revisions
* 4.5 (12) or later - expected general availability before 2001, May 1
* 5.5 (7) or later
* 6.1 (3) or later
are not affected by this vulnerability. Software upgrade can be
performed via the console interface.
No other Cisco product is currently known to be affected by this
vulnerability. This includes the Catalyst 6000, 4000, 3500XL,
2900XL and 2948G switches.
The following workarounds will prevent the 802.1x frames from
causing an 802.1x frames network storm in an affected Catalyst
5000 series switch network. These workarounds can also be
applied to a network experiencing an 802.1x frames network storm.
1. Configure permanent MAC address entries for the entire reserved
STP range 01-80-c2-00-00-02 to 01-80-c2-00-00-0f to be directed
out an unused port for each VLAN on each affected switch in the
network.
The commands to configure are given below.
set cam permanent 01-80-c2-00-00-02 <mod#>/<port#> <VLAN>
set cam permanent 01-80-c2-00-00-03 <mod#>/<port#> <VLAN>
set cam permanent 01-80-c2-00-00-04 <mod#>/<port#> <VLAN>
set cam permanent 01-80-c2-00-00-05 <mod#>/<port#> <VLAN>
set cam permanent 01-80-c2-00-00-06 <mod#>/<port#> <VLAN>
set cam permanent 01-80-c2-00-00-07 <mod#>/<port#> <VLAN>
set cam permanent 01-80-c2-00-00-08 <mod#>/<port#> <VLAN>
set cam permanent 01-80-c2-00-00-09 <mod#>/<port#> <VLAN>
set cam permanent 01-80-c2-00-00-0a <mod#>/<port#> <VLAN>
set cam permanent 01-80-c2-00-00-0b <mod#>/<port#> <VLAN>
set cam permanent 01-80-c2-00-00-0c <mod#>/<port#> <VLAN>
set cam permanent 01-80-c2-00-00-0d <mod#>/<port#> <VLAN>
set cam permanent 01-80-c2-00-00-0e <mod#>/<port#> <VLAN>
set cam permanent 01-80-c2-00-00-0f <mod#>/<port#> <VLAN>
2. Break the STP loop by either
a) Disabling the redundant (STP blocked ports) or
b) Disconnecting the cable from these ports
Remove all the sources of 802.1x frames before re-enabling the
ports or reconnecting the cables.
3. Power down the Catalyst 5000 switch(es) that create the
spanning-tree loop (any switch with STP blocked ports). Remove
all the sources of 802.1x frames before powering up the
switches.
Microsoft Windows XP attempts 802.1x authentication during its
boot-up phase. Following these configuration steps for Microsoft
Windows XP can disable this:
1. Click on the associated Local Area Connection under Network
Connections
2. Click on the Authentication Tab at the top right.
3. Uncheck "Network Access Control using IEEE 802.1x"