30 lines
1.6 KiB
YAML
30 lines
1.6 KiB
YAML
---
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prelude: >
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The ML2 plug-in supports calculating the MTU for instances
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using overlay networks by subtracting the overlay protocol
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overhead from the value of 'path_mtu', ideally the physical
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(underlying) network MTU, and providing the smaller value to
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instances via DHCP. Prior to Mitaka, 'path_mtu' defaults to
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0 which disables this feature. In Mitaka, 'path_mtu' defaults
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to 1500, a typical MTU for physical networks, to improve the
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"out of box" experience for typical deployments.
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features:
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- In Mitaka, the combination of 'path_mtu' defaulting to 1500 and
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'advertise_mtu' defaulting to True provides a value of MTU accounting
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for any overlay protocol overhead on the network to instances using
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DHCP. For example, an instance attaching to a VXLAN network receives
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a 1450 MTU from DHCP accounting for 50 bytes of overhead from the
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VXLAN overlay protocol if using IPv4 endpoints.
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issues:
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- The combination of 'path_mtu' and 'advertise_mtu' only adjusts the
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MTU for instances rather than all virtual network components between
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instances and provider/public networks. In particular, setting
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'path_mtu' to a value greater than 1500 can cause packet loss even
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if the physical network supports it. Also, the calculation does not
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consider additional overhead from IPv6 endpoints.
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upgrade:
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- Operators using the ML2 plug-in with 'path_mtu' defaulting to 0 may need
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to perform a database migration to update the MTU for existing networks
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and possibly disable existing workarounds for MTU problems such as
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increasing the physical network MTU to 1550.
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