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Found an odd behavior on Linux and the VyOS CLI implementation. If adding VXLAN
interfaces using iproute2 the MTU differs depending on the creation syntax:
ip -4 link add vxlan100 type vxlan dstport 4789 external df unset tos inherit \
ttl 16 nolearning vnifilter local 172.16.33.201
ip -4 link add vxlan200 type vxlan id 200 dstport 4789 local 172.16.33.201 dev eth0
ip -6 link add vxlan300 type vxlan id 300 dstport 4789 local 2001:db8:1::1 dev eth0
132: vxlan300: <BROADCAST,MULTICAST> mtu 1430 qdisc noop state DOWN group default qlen 1000
link/ether 4e:fb:e3:f5:d9:59 brd ff:ff:ff:ff:ff:ff
133: vxlan200: <BROADCAST,MULTICAST> mtu 1450 qdisc noop state DOWN group default qlen 1000
link/ether 0e:4e:f4:76:59:3f brd ff:ff:ff:ff:ff:ff
134: vxlan100: <BROADCAST,MULTICAST> mtu 1500 qdisc noop state DOWN group default qlen 1000
link/ether ba:b6:b7:0c:b1:37 brd ff:ff:ff:ff:ff:ff
VyOS always sets a default MTU of 1450 bytes which is correct for IPv4 p2p links
or multicast, but invalid for IPv6 p2p. Also this will break EVPN deployments
as ethernet bridges with MTU < 1500 bytes are less fun.
Increase default MTU to 1500 bytes. Migrate old configurations to use 1450
bytes if not specified otherwise on the CLI.
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As we have a bunch of options under "paramteres" already and "external" is
clearly one of them it should be migrated under that node as well.
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Currently VyOS VXLAN implementation uses the Linux assigned port 8472 that
predates the IANA assignment. As Most other vendors use the IANA assigned port,
follow this guideline and use the new default port 4789.
Existing configuration not defining an explicit port number will be migrated
to the old default port number of 8472, keeping existing configurations work!
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