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The Cisco perimeter switch must be configured to block all packets with any IP options.


Finding ID Version Rule ID IA Controls Severity
V-221015 CISC-RT-000350 SV-221015r856410_rule Medium
Packets with IP options are not fast switched and henceforth must be punted to the switch processor. Hackers who initiate denial-of-service (DoS) attacks on switches commonly send large streams of packets with IP options. Dropping the packets with IP options reduces the load of IP options packets on the switch. The end result is a reduction in the effects of the DoS attack on the switch and on downstream switches.
Cisco IOS XE Switch RTR Security Technical Implementation Guide 2023-09-13


Check Text ( C-22730r408839_chk )
Review the switch configuration to determine if it will block all packets with IP options.

ip access-list extended EXTERNAL_ACL
permit tcp any any established
deny ip any any option any-options
permit …

deny ip any any log-input

If the switch is not configured to drop all packets with IP options, this is a finding.
Fix Text (F-22719r408840_fix)
Configure the switch to drop all packets with IP options.

SW1(config)#ip access-list extended EXTERNAL_ACL
SW1(config-ext-nacl)#15 deny ip any any option any-options