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In some cases, the DHCP relay process may spike up to 99.9% when DHCP snooping is enabled on the VLAN. This will cause ping drops and latency.
diag sys top
dhcprd 1600 R 99.9 1.7 <- CPU showing 99.9%.
Starting from versions 7.4.x and above, FortiSwitch logs will show the top process consuming high CPU. Setting a syslog server will help to monitor the process.
For example:
execute log display
149: 2024-07-23 21:10:40 log_id=0103042920 tz=+1000 type=event subtype=system pri=information vd=root user="cpu_sensor" sample_start="2024-07-23 11:10:34", sample_end="2024-07-23 11:10:40" system_cpu="usr:3,sys:9,nic:4,idle:65,io:0,irq:0,sirq:111" top_processes="[dhcprd]:5.8,[merged_daemons]:3.5,[ctrld]:1.8,[fortilinkd]:1.3,[cu_swtpd]:0.4"msg="CPU usage percentage sample collected."
A similar bug (1021769) is fixed in FortiSwitch version 7.2.8, 7.4.4 and 7.6.0. See the release notes for more information.
If an immediate upgrade is not possible, disable dhcp-snooping on the VLANs temporarily as a workaround.
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