Wednesday, January 30, 2019

EDNS0 large UDP packets

Hello everyone.

Since we deployed a Huawei switch, our users started noticing that the internal Windows DNS server was really slow and timing out with certain frequency.

Apparently the problem is related to EDNS0 that allows larger (> 512 bytes) UDP packets. We disabled this feature and it immediately fixed the issues we were facing.

Microsoft recommendation is to review the network and make sure that all devices is allowing such packets. I'm not sure how can I accomplish that with the Huawei switch. Could be a MTU issue? Everything is using 1500.

We don't have any switch configuration related to MTU or large UDP packets. The DNS server is running on VMware.

Does anyone have any experience that could help me to solve this problem?

Thanks!



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