fix: default linux vrf device mtu for latest linux kernels #1824
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Default mtu for vrf is set to 65536. The value was changed in recent linux kernels to 65535 (ETH_MAX_MTU) + size of IPv6 header (40 octets) resulting in mtu 65575. Latest kernel sets this value by default. I don't know the exact kernel version where the change has taken place, but it was somewhere between 5.11.0-27-generic to 5.11.0-37-generic (tested empirically). More info here: https://www.spinics.net/lists/stable/msg476226.html The patch causes that both values are considered as default in case the new MTU is undefined. Signed-off-by: Vladimir Lavor <vlavor@cisco.com>
ondrej-fabry
approved these changes
Nov 11, 2021
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Default mtu for vrf is set to 65536. The value was changed in recent linux kernels
to 65535 (ETH_MAX_MTU) + size of IPv6 header (40 octets) resulting in mtu 65575.
The latest kernel sets this value by default.
I don't know the exact kernel version where the change has taken place, but it was
somewhere between 5.11.0-27-generic to 5.11.0-37-generic (tested empirically).
More info here: https://www.spinics.net/lists/stable/msg476226.html
Without the patch, resync modifies MTU (from linux-default to agent-default) without
change in the data. The patch causes that both values are considered as default in case
the new MTU is undefined.
Added simple example to localclient-linux testing vrf device.
Signed-off-by: Vladimir Lavor vlavor@cisco.com