From 2bb62b43bf8b3d95e199b111d8f6de01890c0536 Mon Sep 17 00:00:00 2001
From: Brian Haley <bhaley@redhat.com>
Date: Fri, 6 Nov 2020 17:34:53 -0500
Subject: [PATCH] Decrease MTU to account for IPv6 header

(MTU - 50) only supports VxLAN over IPv4, decrease it
to support IPv6 as well, which is 20 bytes larger.

Change-Id: I0cf258770f628c1b4fb590bd274b5433fbcc1450
---
 playbooks/pre.yaml | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/playbooks/pre.yaml b/playbooks/pre.yaml
index ff97a1f501..68cb1d8c7a 100644
--- a/playbooks/pre.yaml
+++ b/playbooks/pre.yaml
@@ -19,12 +19,13 @@
           {% endfor -%}
           {{- mtus|min -}}
     - name: Calculate external_bridge_mtu
-      # 50 bytes is overhead for vxlan (which is greater than GRE
+      # 30 bytes is overhead for vxlan (which is greater than GRE
       # allowing us to use either overlay option with this MTU.
+      # 40 bytes is overhead for IPv6, which will also support an IPv4 overlay.
       # TODO(andreaf) This should work, but it may have to be reconcilied with
       # the MTU setting used by the multinode setup roles in multinode pre.yaml
       set_fact:
-        external_bridge_mtu: "{{ local_mtu | int - 50 }}"
+        external_bridge_mtu: "{{ local_mtu | int - 30 - 40 }}"
   roles:
     - configure-swap
     - setup-stack-user