From 4a163b016333e58fee9d6ec6b53a09e0160b3213 Mon Sep 17 00:00:00 2001
From: Christian Breunig <christian@breunig.cc>
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: <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.
---
src/migration-scripts/interfaces/31-to-32 | 4 ++++
1 file changed, 4 insertions(+)
(limited to 'src')
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 <http://www.gnu.org/licenses/>.
#
# 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())
--
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