Problem: CPUHOG Messages During Adjacency Formation-Cause: Router Is Not Running Packet-Pacing Code

Problem: CPUHOG Messages During Adjacency Formation ‚ Cause: Router Is Not Running Packet-Pacing Code

When OSPF forms an adjacency, it floods all its link-state packets to its neighbor. This flooding sometimes takes a lot of CPU. Also, releases of Cisco IOS Software before 12.0T did not support packet pacing, which means that a router will try to send data as fast as it can over a link. If a link is slow or the router on the other side is slow in responding, this results in retransmission of the LSA and eventually leads to CPUHOG messages. Packet pacing adds a pacing interval between the LS updates. Instead of flooding everything at once, its sends the packet with a gap of a few milliseconds in between. Figure 9-87 shows the flowchart to follow to solve this problem.

Figure 9-87. Problem-Resolution Flowchart

Debugs and Verification

CPUHOG messages can be seen on a console of a router during adjacency formation and later can be checked with the show log command. Example 9-242 shows the log messages on a router showing CPUHOG.

Example 9-242 Log Messages Showing CPUHOG by OSPF Router

 R1#  show log   %SYS-3-CPUHOG: Task ran for 2424 msec (15/15), process = OSPF Router  %SYS-3-CPUHOG: Task ran for 2340 msec (10/9), process = OSPF Router %SYS-3-CPUHOG: Task ran for 2264 msec (0/0), process = OSPF Router 

Solution

Packet pacing introduces a delay of 33 ms between packets and 66 ms between retransmissions. This pacing interval reduces the CPUHOG messages, and the adjacency is formed more quickly. This feature is on by default in Cisco IOS Software Release 12.0T and later. This feature is not available in the Cisco IOS Software releases earlier than 12.0T. If you are running Cisco IOS Software code earlier than Release 12.0T and you are seeing CPUHOG messages during adjacency formation, upgrade to at least Cisco IOS Software Release 12.0T or higher code to solve this problem through packet pacing.