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5212 phones have an invalid DHCP option 124 - new Cisco gear incompatible

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handwritten:
This is an odd one. We use DHCP relay on a Cisco 9500 core switch. We recently upgraded from 16.something to 17.3.4, and now all the DHCP Discover messages from 5212 phones are getting dropped by the core. The core gives us an error "DHCPD: Invalid option 124 information. Dropping DHCP message". I confirmed with a packet capture that the option 124 'V-I Vendor Class' in Discover messages from those phones is 4 bytes long, where the standard is 5 bytes or longer. Wireshark flags this as an error. This seems to be the bug ('caveat') that Cisco acknowledges here: https://bst.cloudapps.cisco.com/bugsearch/bug/CSCvt34738. We have not tried the proposed workaround because it's not relevant for our environment. We're currently stumped.

ralph:
Maybe the easiest thing to do might be to put the phone in teleworker mode.
Boot the device holding the 7 key and point it to your primary controller.

Ralph

handwritten:
That's an interesting idea. As a workaround we spun up another DHCP server (with non-overlapping scope) on the voice VLAN itself so that no 'Helper Address' is required on the core.

Ronan:
Hello, I'm having the same issue with a client still using old phones (and in MCD 6.0).

He's asking if putting the phones in SIP mode could help, any ideas about that ? He's probably anticipating that Mitel will say it's fixed in 9.0 or 10.0 or whatever but doesn't have the budget to upgrade.

lundah:

--- Quote from: Ronan on April 16, 2024, 03:52:44 AM ---Hello, I'm having the same issue with a client still using old phones (and in MCD 6.0).

He's asking if putting the phones in SIP mode could help, any ideas about that ? He's probably anticipating that Mitel will say it's fixed in 9.0 or 10.0 or whatever but doesn't have the budget to upgrade.

--- End quote ---

Sounds like it's a Cisco issue and not a Mitel issue, so I don't see how upgrading the Mitel will help.

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