NET0949 - Cisco Express Fowarding (CEF) not enabled on supported devices

Information

Cisco Express Forwarding (CEF) must be enabled on all supported Cisco Layer 3 IP devices.

The Cisco Express Forwarding (CEF) switching mode replaces the traditional Cisco routing cache with a data structure that mirrors the entire system routing table. Because there is no need to build cache entries when traffic starts arriving for new destinations, CEF behaves more predictably when presented with large volumes of traffic addressed to many destinations such as a SYN flood attacks. Because many SYN flood attacks use randomized source addresses to which the hosts under attack will reply to, there can be a substantial amount of traffic for a large number of destinations that the router will have to handle. Consequently, routers configured for CEF will perform better under SYN floods directed at hosts inside the network than routers using the traditional cache.

Solution

1. If the Cisco Layer 3 IP device not enabled by default, enable Distributed CEF Mode globally.

Router(config)# ip cef distributed

2. If Distributed CEF Mode is not supported, enable Centralized CEF Mode globally.

Router(config)# ip cef

3. If CEF is not supported in any capacity on the device, this finding is N/A.

See Also

https://iasecontent.disa.mil/stigs/zip/U_Network_Infrastructure_Router_L3_Switch_V8R29_STIG.zip

Item Details

Category: CONFIGURATION MANAGEMENT

References: 800-53|CM-7, CAT|II, CSCv6|9.1, Rule-ID|SV-5645r4_rule, STIG-ID|NET0949, Vuln-ID|V-5645

Plugin: Cisco

Control ID: 6b42992defcf22d4516de2a2b6e26c8c96e4c9dd7c75c4874ff853299e6b23ce