DHCP relay on IOS XE 17.3.3 not relaying certain packets
We recently upgraded a 9200L-48T and a 9300-48T-A switch to this version, and immediately had troubles with MITEL phones, models 5220 and 5224, which were no longer able to communicate via the DHCP relay on SVIs on their VLAN.
Specifically, option 124 on these phones is set at a 4-byte length (which apparently goes against a DHCP standard?? If so, the RFC does not mention it), and Cisco now drops these packets and won’t relay them ("DHCPD: Invalid option 124 information. Dropping DHCP message"). The string for option 124 in hex appears as “7c 04 00 00 04 03” (translates to option 124, 4 byte length, Enterprise ID 1027), whereas on a working set of a different model for instance, appears as “7c 05 00 00 04 03 00” (translates to option 124, 5 byte length, Enterprise ID 1027).
Can someone clarify why there is now a 5-byte requirement for the Enterprise ID in Option 124, even if it's just padded with an octet of 0?
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