doc: add discussion for a handful of nhrp commands

Signed-off-by: Jafar Al-Gharaibeh <jafar@atcorp.com>

doc/user/nhrpd.rst

@@ -4,8 +4,8 @@
 NHRP
 ****
 
-*nhrpd* is an implementation of the :abbr:NHRP `(Next Hop Routing Protocol)`.
+*nhrpd* is an implementation of the :abbr:`NHRP (Next Hop Routing Protocol)`.
-NHRP is described in :rfc`2332`.
+NHRP is described in :rfc:`2332`.
 
 NHRP is used to improve the efficiency of routing computer network traffic over
 :abbr:`NBMA (Non-Broadcast, Multiple Access)` networks. NHRP provides an
@@ -13,6 +13,13 @@ ARP-like solution that allows a system to dynamically learn the NBMA address of
 the other systems that are part of that network, allowing these systems to
 directly communicate without requiring traffic to use an intermediate hop.
 
+NHRP is a client-server protocol. The server side is called the :abbr:`NHS
+(Next Hop Server)` or the hub, while a client is referred to as the :abbr:`NHC
+(Next Hop Client)` or the spoke. When a node is configured as an NHC, it
+registers its address with the NHS which keeps track of all registered spokes.
+An NHC client can then query the addresses of other clients from NHS allowing
+all spokes to communicate directly with each other.
+
 Cisco Dynamic Multipoint VPN (DMVPN) is based on NHRP, and |PACKAGE_NAME| nhrpd
 implements this scenario.
 
@@ -31,7 +38,9 @@ This is similar to Cisco FlexVPN; but in contrast to opennhrp which uses
 a generic subnet route.
 
 To create NBMA GRE tunnel you might use the following (Linux terminal
-commands):::
+commands):
+
+.. code-block:: console
 
    ip tunnel add gre1 mode gre key 42 ttl 64
    ip addr add 10.255.255.2/32 dev gre1
@@ -68,7 +77,58 @@ command defines the GRE subnet):
 Configuring NHRP
 ================
 
-FIXME
+.. index::  ip nhrp holdtime (1-65000)
+.. clicmd:: ip nhrp holdtime (1-65000)
+
+   Holdtime is the number of seconds that have to pass before stopping to
+   advertise an NHRP NBMA address as valid. It also controls how often NHRP
+   registration requests are sent. By default registrations are sent every one
+   third of the holdtime.
+
+.. index::  ip nhrp map A.B.C.D|X:X::X:X A.B.C.D|local
+.. clicmd:: ip nhrp map A.B.C.D|X:X::X:X A.B.C.D|local
+
+   Map an IP address of a station to the station's NBMA address.
+
+.. index::  ip nhrp network-id (1-4294967295)
+.. clicmd:: ip nhrp network-id (1-4294967295)
+
+   Enable NHRP on this interface and set the interface's network ID.  The
+   network ID is used to allow creating multiple nhrp domains on a router when
+   multiple interfaces are configured on the router.  Interfaces configured
+   with the same ID are part of the same logical NBMA network. The ID is a
+   local only parameter and is not sent to other NHRP nodes and so IDs on
+   different nodes do not need to match. When NHRP packets are received on an
+   interface they are assigned to the local NHRP domain for that interface.
+
+.. index::  ip nhrp nhs A.B.C.D nbma A.B.C.D|FQDN
+.. clicmd:: ip nhrp nhs A.B.C.D nbma A.B.C.D|FQDN
+
+   Configure the Next Hop Server address and its NBMA address.
+
+.. index::  ip nhrp nhs dynamic nbma A.B.C.D
+.. clicmd:: ip nhrp nhs dynamic nbma A.B.C.D
+
+   Configure the Next Hop Server to have a dynamic address and set its NBMA
+   address.
+
+.. index::  ip nhrp registration no-unique
+.. clicmd:: ip nhrp registration no-unique
+
+   Allow the client to not set the unique flag in the NHRP packets. This is
+   useful when a station has a dynamic IP address that could change over time.
+
+.. index::  ip nhrp shortcut
+.. clicmd:: ip nhrp shortcut
+
+   Enable shortcut (spoke-to-spoke) tunnels to allow NHC to talk to each others
+   directly after establishing a connection without going through the hub.
+
+.. index::  ip nhrp mtu
+.. clicmd:: ip nhrp mtu
+
+   Configure NHRP advertised MTU.
+
 
 .. _hub-functionality:
 
@@ -92,25 +152,25 @@ This can be achieved with the following iptables rule.
        --hashlimit-name loglimit-0 -j NFLOG --nflog-group 1 --nflog-range 128
 
 
-You can fine tune the src/dstmask according to the prefix lengths you
+You can fine tune the src/dstmask according to the prefix lengths you announce
-announce internal, add additional IP range matches, or rate limitation
+internal, add additional IP range matches, or rate limitation if needed.
-if needed. However, the above should be good in most cases.
+However, the above should be good in most cases.
 
 This kernel NFLOG target's nflog-group is configured in global nhrp config
 with:
 
-.. code-block:: frr
+.. index::  nhrp nflog-group (1-65535)
-
+.. clicmd:: nhrp nflog-group (1-65535)
-   nhrp nflog-group 1
 
 To start sending these traffic notices out from hubs, use the nhrp
 per-interface directive:
 
-.. code-block:: frr
+.. index::  ip nhrp redirect
-
+.. clicmd:: ip nhrp redirect
-   interface gre1
-    ip nhrp redirect
 
+This enable redirect replies on the NHS similar to ICMP redirects except this
+is managed by the nhrp protocol. This setting allows spokes to communicate with
+each others directly.
 
 .. _integration-with-ike:
 
@@ -134,7 +194,10 @@ git repositories for the patches.
 NHRP Events
 ===========
 
-FIXME
+.. index::  nhrp event socket SOCKET
+.. clicmd:: nhrp event socket SOCKET
+
+   Configure the Unix path for the event socket.
 
 Configuration Example
 =====================