Signed-off-by: Han Zhou <[email protected]>
---
ovn-architecture.7.xml | 50 ++++++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 50 insertions(+)
diff --git a/ovn-architecture.7.xml b/ovn-architecture.7.xml
index 3340770..1f8aa2b 100644
--- a/ovn-architecture.7.xml
+++ b/ovn-architecture.7.xml
@@ -1733,6 +1733,56 @@
http://docs.openvswitch.org/en/latest/topics/high-availability.
</p>
+ <h3>Restrictions of Distributed Gateway Ports</h3>
+
+ <p>
+ Distributed gateway ports are used to connect to an external network, which
+ can be a physical network modeled by a logical switch with a localnet port,
+ and can also be a logical switch that interconnects different OVN
+ deployments (see <code>OVN Deployments Interconnection</code>). Usually
+ there can be many logical routers connected to the same external logical
+ switch, as shown in below diagram.
+ </p>
+
+ <pre fixed="yes">
+ +--LS-EXT-+
+ | | |
+ | | |
+ LR1 ... LRn
+ </pre>
+
+ <p>
+ In this diagram, there are n logical routers connected to a logical switch
+ LS-EXT, each with a distributed gateway port, so that traffic sent to
+ external world is redirected to the gateway chassis that is assigned to the
+ distributed gateway port of respective logical router.
+ </p>
+
+ <p>
+ In the logical topology, nothing can prevent an user to add a route between
+ the logical routers via the connected distributed gateway ports on LS-EXT.
+ However, the route works only if the LS-EXT is a physical network (modeled
+ by a logical switch with a localnet port). In that case the packet will
+ be delivered between the gateway chassises through the localnet port via
+ physical network. If the LS-EXT is a regular logical switch (backed by
+ tunneling only, as in the use case of OVN interconnection), then the packet
+ will be dropped on the source gateway chassis. The limitation is due the
+ fact that distributed gateway ports are tied to physical location, and
+ without physical network connection, we will end up with either dropping
+ the packet or transferring it over the tunnels which could cause bigger
+ problems such as broadcast packets being redirect repeatedly by different
+ gateway chassises.
+ </p>
+
+ <p>
+ With the limitation in mind, if a user do want the direct connectivity
+ between the logical routers, it is better to create an internal logical
+ switch connected to the logical routers with regular logical router ports,
+ which are completely distributed and the packets don't have to leave
+ a chassis unless necessary, which is more optimal than routing via the
+ distributed gateway ports.
+ </p>
+
<h3>ARP request and ND NS packet processing</h3>
<p>
--
2.1.0
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