CCNP R&S Question of the Week: CPU Spike

Refer to the following access list:

access-list 100 permit ip any any log

After applying the access list on a Cisco router, the network engineer notices that the router CPU has spiked to 99 percent. Why?

A. A packet that matches access-list with the “log” keyword is Cisco Express Forwarding switched.
B. A packet that matches access-list with the “log” keyword is fast switched.
C. A packet that matches access-list with the “log” keyword is process switched.
D. A large amount of IP traffic is being permitted on the router.

Reveal Answer

Answer: C.

 

Logging-enabled access control lists (ACLs) provide insight into traffic as it traverses the network or is dropped by network devices. Unfortunately, ACL logging can be CPU intensive and can negatively affect other functions of the network device. There are two primary factors that contribute to the CPU load increase from ACL logging: process switching of packets that match log-enabled access control entries (ACEs) and the generation and transmission of log messages themselves.

 

Related Courses
ROUTE – Implementing Cisco IP Routing v2.0
SWITCH – Implementing Cisco IP Switched Networks v2.0
TSHOOT – Troubleshooting and Maintaining Cisco IP Networks v2.0

Related Certification
CCNP Routing and Switching

CCNP R&S Question of the Week Series

• CCNP R&S Question of the Week: IPv6
• CCNP R&S Question of the Week: BGP Attribute
• CCNP R&S Question of the Week: Gateway of Last Resort
• CCNP R&S Question of the Week: Routing Protocols into OSPF
• CCNP R&S Question of the Week: BPDU Guard
• CCNP R&S Question of the Week: Private VLANs
• CCNP R&S Question of the Week: Blocking to Forwarding State
• CCNP R&S Question of the Week: FTP to HTTP
• CCNP R&S Question of the Week: Alerts
• CCNP R&S Question of the Week: Configuration Sequence
• CCNP R&S Question of the Week: TCP Traffic
• CCNP R&S Question of the Week: IPv4 and IPv6
• CCNP R&S Question of the Week: clear ip route
• CCNP R&S Question of the Week: IPv6 Traffic Filter Impact
• CCNP R&S Question of the Week: EtherChannel
• CCNP R&S Question of the Week: Interface FastEthernet0/1
• CCNP R&S Question of the Week: Directly Connected CDP Devices
• CCNP R&S Question of the Week: IPsec Modes
• CCNP R&S Question of the Week: Troubleshooting an EIGRP Problem
• CCNP R&S Question of the Week: CPU Spike

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