From 4a163b016333e58fee9d6ec6b53a09e0160b3213 Mon Sep 17 00:00:00 2001 From: Christian Breunig Date: Wed, 22 Nov 2023 10:52:40 +0100 Subject: vxlan: T5759: change default MTU from 1450 -> 1500 bytes 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: 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: 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: 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. --- src/migration-scripts/interfaces/31-to-32 | 4 ++++ 1 file changed, 4 insertions(+) (limited to 'src/migration-scripts') diff --git a/src/migration-scripts/interfaces/31-to-32 b/src/migration-scripts/interfaces/31-to-32 index ca3d19320..0fc27b70a 100755 --- a/src/migration-scripts/interfaces/31-to-32 +++ b/src/migration-scripts/interfaces/31-to-32 @@ -15,6 +15,7 @@ # along with this program. If not, see . # # T5671: change port to IANA assigned default port +# T5759: change default MTU 1450 -> 1500 from sys import argv from sys import exit @@ -43,6 +44,9 @@ for vxlan in config.list_nodes(base): if not config.exists(base + [vxlan, 'port']): config.set(base + [vxlan, 'port'], value='8472') + if not config.exists(base + [vxlan, 'mtu']): + config.set(base + [vxlan, 'mtu'], value='1450') + try: with open(file_name, 'w') as f: f.write(config.to_string()) -- cgit v1.2.3