Talk:News/2025 Cloud VPS VXLAN IPv6 migration

MTU on new network

One difference that took me a while to figure out is that VMs on this new network get network interfaces with an MTU of 1450:

$ ip addr show ens3 | grep mtu
2: ens3: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1450 qdisc fq_codel state UP group default qlen 1000

Note that the old "legacy" network used mtu=1500.

Since for my use case I create multiple docker containers that try to reach the internet, I was getting subtle network failures due to docker creating network interfaces that defaulted to the typical mtu=1500. Sharing this for if it is worth adding to the FAQ section here.

More info at https://phabricator.wikimedia.org/T408019#11380117. XCollazo-WMF (talk) 21:11, 17 November 2025 (UTC)

You independently rediscovered phab:T408543. -- BryanDavis (talk) 21:32, 17 November 2025 (UTC)