diff --git a/doc/glossary/glossary-terms.xml b/doc/glossary/glossary-terms.xml
index 592142629b..e0e3fc6df6 100644
--- a/doc/glossary/glossary-terms.xml
+++ b/doc/glossary/glossary-terms.xml
@@ -3455,9 +3455,9 @@
- Generic Routing Encapsulation (GRE)
+ generic routing encapsulation (GRE)
- Generic Routing Encapsulation (GRE)
+ networks
Protocol that encapsulates a wide variety of network
@@ -4361,6 +4361,18 @@
+
+ internet protocol (IP)
+
+ networks
+
+
+
+ Principal communications protocol in the internet protocol
+ suite for relaying datagrams across network boundaries.
+
+
+
Internet Service Provider (ISP)
@@ -4578,6 +4590,18 @@
+
+ jumbo frames
+
+ networks
+
+
+
+ Feature in modern Ethernet networks that supports frames up to
+ approximately 9000 bytes.
+
+
+
Juno
@@ -4921,6 +4945,18 @@
+
+ maximum transmission unit (MTU)
+
+ networks
+
+
+
+ Maximum frame or packet size for a particular network
+ medium. Typically 1500 bytes for Ethernet networks.
+
+
+
melange
@@ -5924,6 +5960,18 @@
+
+ path MTU discovery (PMTUD)
+
+ networks
+
+
+
+ Mechanism in IP networks to detect end-to-end MTU and adjust
+ packet size accordingly.
+
+
+
pause
diff --git a/doc/install-guide/section_neutron-ml2-network-node.xml b/doc/install-guide/section_neutron-ml2-network-node.xml
index af1419e4c4..fecd858cbf 100644
--- a/doc/install-guide/section_neutron-ml2-network-node.xml
+++ b/doc/install-guide/section_neutron-ml2-network-node.xml
@@ -248,6 +248,62 @@ use_namespaces = True
file.
+
+ Tunneling protocols such as
+ generic routing encapsulation (GRE)
+ include additional packet headers that increase overhead and
+ decrease space available for the payload or user data. Without
+ knowledge of the virtual network infrastructure, instances attempt
+ to send packets using the default Ethernet
+ maximum transmission unit (MTU) of 1500 bytes.
+ Internet protocol (IP) networks contain the
+ path MTU discovery (PMTUD) mechanism to detect
+ end-to-end MTU and adjust packet size accordingly. However, some
+ operating systems and networks block or otherwise lack support for
+ PMTUD causing performance degradation or connectivity failure.
+ Ideally, you can prevent these problems by enabling
+ jumbo frames on the physical network that
+ contains your tenant virtual networks. Jumbo frames support MTUs
+ up to approximately 9000 bytes which negates the impact of GRE
+ overhead on virtual networks. However, many network devices lack
+ support for jumbo frames and OpenStack administrators often lack
+ control of network infrastructure. Given the latter complications,
+ you can also prevent MTU problems by reducing the instance MTU to
+ account for GRE overhead. Determining the proper MTU value often
+ takes experimentation, but 1454 bytes works in most environments.
+ You can configure the DHCP server that assigns
+ IP addresses to your instances to also adjust the MTU.
+
+ Some cloud images such as CirrOS ignore the DHCP MTU
+ option.
+
+
+
+ Edit the /etc/neutron/dhcp_agent.ini
+ file and add the following keys to the
+ [DEFAULT] section:
+ [DEFAULT]
+...
+dnsmasq_config_file = /etc/neutron/dnsmasq-neutron.conf
+
+
+ Run the following command:
+ # openstack-config --set /etc/neutron/dhcp_agent.ini DEFAULT \
+ dnsmasq_config_file /etc/neutron/dnsmasq-neutron.conf
+
+
+ Create and edit the
+ /etc/neutron/dnsmasq-neutron.conf file and
+ add the following keys:
+ dhcp-option-force=26,1454
+
+
+ Kill any existing
+ dnsmasq processes:
+ # killall dnsmasq
+
+
+
To configure the metadata agent