DNS_EVENT_BAD_PACKET_LENGTH (Event ID 5501) on Windows Server 2022

[Holli69]

Hi,

when we update the MX Firmware from 19.1.12 to stable Firmware 19.2.7, we get DNS_EVENT_BAD_PACKET_LENGTH (Event ID 5501) and the oversized DNS packets (EDNS0) are thrown away.

Had anyone the same issue in the past or yet and a solution for this behaviour ?

If we switched back again to 19.1.12, everything is okay without Event ID 5501.

So something changed between this 2 versions. Maybe, it's because of the IKEv2/Diffie Hellmann stronger encryption ?

[Tony-Sydney-AU]

Hi @Holli69 ,

That's an interesting behaviour. I haven't seen EDNS0 sent from MX in a very long time.

We would need more details from you and perhaps this would be better handled over a support case.

In the meantime, can you clarify the following:

1) is your Windows server querying a DNS server behind a VPN tunnel?

2) If DNS is behind a VPN tunnel, is it another MX or is it a non-Meraki VPN?

3) Does this event happens to any / all DNS queries?

Looking forward to your input on this.