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Interface MTU change on AWS instances supporting Jumbo packets #2443
Between Container Linux releases, the default interface MTU used on AWS instances supporting Jumbo packets has changed/regressed from 9001 to 1500. This causes connectivity problems between pods across node boundaries. CNI providers don't expect the MTU to change over time node-by-node. It also means Jumbo packets aren't being used. I received pages shortly after the OS auto-update occurred.
Container Linux Version
Launch an EC2 instance that supports Jumbo packets. A
Now try with stable 1745.3.1 or 1745.4.0. The MTU has changed to 1500, as though Jumbo frame support isn't available.
This was referenced
May 27, 2018
I'm not too familiar with such network details, but I guess that AWS is pushing the MTU parameter via DHCP and
Can you please:
Seems like a good guess. It looks like its attempting to set the MTU and now failing. On 1688.5.3,
and on 1745.4.0,
I haven't found anything notable or different in the run locations.
Thanks. I'm observing this on latest alpha too, and it seems to have started with the systemd-v238 bump (unrelated to kernel version). I forwarded this to systemd/systemd#9102 with some additional details, but I failed to locate where the real issue is. Waiting for some more insights from upstream.
Thanks for fixing this. I've been chasing load balancer PMTU problems and tracked it back to this. I saw this issue when updating to
I am guessing that while T2 and other instance types support jumbo frames, T2 instances perhaps default to 1500 whereas the others default to 9001 (before DHCP overrides that).