From c7e1de09e1fd221ab9d5880165baaa3f34678c35 Mon Sep 17 00:00:00 2001 From: Slawek Kaplonski Date: Wed, 16 Jun 2021 14:03:33 +0200 Subject: [PATCH] [Docs] Add info about vlan transparent networks' MTU MTU configured inside instances which are connected to the networks with enabled transparent vlan needs to have MTU set to 4 bytes less than it is provided by DHCP to make space for additional vlan header. This is required only if instance will have some vlan tagged interfaces configured. Closes-bug: #1906318 Change-Id: Ia6691cbe35a1e874857ec94660ac4b1850586305 --- doc/source/admin/config-mtu.rst | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/doc/source/admin/config-mtu.rst b/doc/source/admin/config-mtu.rst index 73955d56389..4207809e46d 100644 --- a/doc/source/admin/config-mtu.rst +++ b/doc/source/admin/config-mtu.rst @@ -129,3 +129,12 @@ while the L3 agent provides an appropriate MTU value to instances using IPv6. IPv6 uses RA via the L3 agent because the DHCP agent only supports IPv4. Instances using IPv4 and IPv6 should obtain the same MTU value regardless of method. + +Networks with enabled vlan transparency +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +In case of networks with enabled vlan transparency, if additional vlan tag is +configured inside guest VM, MTU has to be lowered by 4 bytes to make space for +additional vlan tag in the packet's header. +For example, if network's MTU is set to ``1500``, value configured for the +interfaces in the guest vm should be manually set to ``1496`` or less bytes.