Cisco Catalyst 2900XL switch allows a remote attacker to create a denial of service via an empty UDP packet sent to port 161 (SNMP) when SNMP is disabled.
https://exchange.xforce.ibmcloud.com/vulnerabilities/6515
https://euvd.enisa.europa.eu/vulnerability/EUVD-2001-0558
http://archives.neohapsis.com/archives/bugtraq/2001-05/0040.html