Switch dropping DHCP packets due to high packet rate.

MVP
MVP
Problem:

There is a rate-limit applied on DHCP packets when DHCP-snooping is enabled. Hence when DHCP packets are received at too high a rate, some may be dropped by the switch.



Diagnostics:

"show logging" would show the error related to DHCP rate limit when DHCP-Snooping is enabled. 

 

W 04/05/18 09:08:01 02698 dhcp-snoop: ST2-CMDR: backplane: DHCP packets are

            dropped at port 2/A1 due to high packet rate.

 

"show running-configuration" would show the configuration related to DHCP-Snooping.

 

interface Trk1
   dhcp-snooping trust
   exit

dhcp-snooping
dhcp-snooping vlan 1-4094


Solution

 

When DHCP snooping is enabled, a rule to snoop DHCP packets will be applied at the CPU and this will rate limit the packets to 100 packets per second. Any DHCP packets exceeding 100 PPS will be dropped by the switch. This is fixed value and cannot be configured. Ideally, DHCP discover messages are retransmitted by all types of clients multiple times, so a packet that is dropped would reappear/retransmitted by clientsand will go through DHCP process successfully .

Version history
Revision #:
1 of 1
Last update:
a month ago
Updated by:
 
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