doc: add BGP VRF use case

This commit brings some information about BGP VRF case with peering
using multiple VRF instances.

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

diff --git a/doc/user/bgp.rst b/doc/user/bgp.rst
index 70b4e51cbec84671dd5134bd926caab8a280b3c4..bc3116d8c288f81b3ddc8310b0ebd2e2c8a2cd2f 100644 (file)
--- a/doc/user/bgp.rst
+++ b/doc/user/bgp.rst
@@ -1547,6 +1547,15 @@ BPGD supports multiple VRF instances via the *router bgp* command:
 VRFNAME is matched against VRFs configured in the kernel. When no *vrf VRFNAME*
 is specified, the BGP protocol process belongs to the default VRF.
 
+With VRF, you can isolate networking information. Having BGP VRF allows you to
+have several BGP instances on the same system process. This solution solves
+scalabiliy issues where the network administrator had previously to run separately
+several BGP processes on each namespace. Now, not only BGP VRF solves this, but
+also this method applies to both kind of VRFs backend: default VRF from Linux kernel
+or network namespaces. Also, having separate BGP instances does not imply that the
+AS number has to be different. For internal purposes, it is possible to do iBGP
+peering from two differents network namespaces.
+
 BGP routes may be leaked (i.e., copied) between a unicast VRF RIB and the VPN
 safi RIB of the default VRF (leaking is also permitted between the unicast RIB
 of the default VRF and VPN).  A shortcut syntax is also available for