doc: add some documentation about bgp evpn netns support

a linux configuration gives some explanation on how to set up an evpn
overlay in network namespaces.

Signed-off-by: Philippe Guibert <philippe.guibert@6wind.com>

diff --git a/doc/user/bgp.rst b/doc/user/bgp.rst
index 84be461cce8b9591817037e33e8a1fa258f637e9..7c86cac11c3970ab44cdf05fbbc6f7cf13555d17 100644 (file)
--- a/doc/user/bgp.rst
+++ b/doc/user/bgp.rst
@@ -2391,6 +2391,27 @@ the same behavior of using same next-hop and RMAC values.
 Enables or disables advertise-pip feature, specifiy system-IP and/or system-MAC
 parameters.
 
+Support with VRF network namespace backend
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+It is possible to separate overlay networks contained in VXLAN interfaces from
+underlay networks by using VRFs. VRF-lite and VRF-netns backends can be used for
+that. In the latter case, this is necessary to set both bridge and vxlan interface
+on the same network namespace, as below example illustrates:
+
+.. code-block:: shell
+
+   # linux shell
+   ip netns add vrf1
+   ip link add name vxlan101 type vxlan id 101 dstport 4789 dev eth0 local 10.1.1.1
+   ip link set dev vxlan101 netns vrf1
+   ip netns exec vrf1 ip link set dev lo up
+   ip netns exec vrf1 brctl addbr bridge101
+   ip netns exec vrf1 brctl addif bridge101 vxlan101
+
+This makes possible to separate not only layer 3 networks like VRF-lite networks.
+Also, VRF netns based make possible to separate layer 2 networks on separate VRF
+instances.
+
 .. _bgp-cisco-compatibility:
 
 Cisco Compatibility