doc/user/nhrpd.rst

   1 .. _NHRP:
   2
   3 ****
   4 NHRP
   5 ****
   6
   7 *nhrpd* is a daemon to support Next Hop Routing Protocol (NHRP).
   8 NHRP is described in RFC2332.
   9
  10 NHRP is used to improve the efficiency of routing computer network
  11 traffic over Non-Broadcast, Multiple Access (NBMA) Networks. NHRP provides
  12 an ARP-like solution that allows a system to dynamically learn the NBMA
  13 address of the other systems that are part of that network, allowing
  14 these systems to directly communicate without requiring traffic to use
  15 an intermediate hop.
  16
  17 Cisco Dynamic Multipoint VPN (DMVPN) is based on NHRP, and
  18 |PACKAGE_NAME| nhrpd implements this scenario.
  19
  20 .. _Routing_Design:
  21
  22 Routing Design
  23 ==============
  24
  25 nhrpd never handles routing of prefixes itself. You need to run some
  26 real routing protocol (e.g. BGP) to advertise routes over the tunnels.
  27 What nhrpd does it establishes 'shortcut routes' that optimizes the
  28 routing protocol to avoid going through extra nodes in NBMA GRE mesh.
  29
  30 nhrpd does route NHRP domain addresses individually using per-host prefixes.
  31 This is similar to Cisco FlexVPN; but in contrast to opennhrp which uses
  32 a generic subnet route.
  33
  34 To create NBMA GRE tunnel you might use the following (linux terminal
  35 commands):
  36 ::
  37
  38    ip tunnel add gre1 mode gre key 42 ttl 64
  39    ip addr add 10.255.255.2/32 dev gre1
  40    ip link set gre1 up
  41
  42
  43 Note that the IP-address is assigned as host prefix to gre1. nhrpd will
  44 automatically create additional host routes pointing to gre1 when
  45 a connection with these hosts is established.
  46
  47 The gre1 subnet prefix should be announced by routing protocol from the
  48 hub nodes (e.g. BGP 'network' announce). This allows the routing protocol
  49 to decide which is the closest hub and determine the relay hub on prefix
  50 basis when direct tunnel is not established.
  51
  52 nhrpd will redistribute directly connected neighbors to zebra. Within
  53 hub nodes, these routes should be internally redistributed using some
  54 routing protocol (e.g. iBGP) to allow hubs to be able to relay all traffic.
  55
  56 This can be achieved in hubs with the following bgp configuration (network
  57 command defines the GRE subnet):
  58 ::
  59
  60   router bgp 65555
  61    address-family ipv4 unicast
  62      network 172.16.0.0/16
  63      redistribute nhrp
  64    exit-address-family
  65
  66
  67 .. _Configuring_NHRP:
  68
  69 Configuring NHRP
  70 ================
  71
  72 FIXME
  73
  74 .. _Hub_Functionality:
  75
  76 Hub Functionality
  77 =================
  78
  79 In addition to routing nhrp redistributed host prefixes, the hub nodes
  80 are also responsible to send NHRP Traffic Indication messages that
  81 trigger creation of the shortcut tunnels.
  82
  83 nhrpd sends Traffic Indication messages based on network traffic captured
  84 using NFLOG. Typically you want to send Traffic Indications for network
  85 traffic that is routed from gre1 back to gre1 in rate limited manner.
  86 This can be achieved with the following iptables rule.
  87
  88 ::
  89
  90   iptables -A FORWARD -i gre1 -o gre1 \\
  91         -m hashlimit --hashlimit-upto 4/minute --hashlimit-burst 1 \\
  92         --hashlimit-mode srcip,dstip --hashlimit-srcmask 24 --hashlimit-dstmask 24 \\
  93         --hashlimit-name loglimit-0 -j NFLOG --nflog-group 1 --nflog-range 128
  94
  95
  96 You can fine tune the src/dstmask according to the prefix lengths you
  97 announce internal, add additional IP range matches, or rate limitation
  98 if needed. However, the above should be good in most cases.
  99
 100 This kernel NFLOG target's nflog-group is configured in global nhrp config
 101 with:
 102 ::
 103
 104   nhrp nflog-group 1
 105
 106
 107 To start sending these traffic notices out from hubs, use the nhrp
 108 per-interface directive:
 109 ::
 110
 111   interface gre1
 112    ip nhrp redirect
 113
 114
 115 .. _Integration_with_IKE:
 116
 117 Integration with IKE
 118 ====================
 119
 120 nhrpd needs tight integration with IKE daemon for various reasons.
 121 Currently only strongSwan is supported as IKE daemon.
 122
 123 nhrpd connects to strongSwan using VICI protocol based on UNIX socket
 124 (hardcoded now as /var/run/charon.vici).
 125
 126 strongSwan currently needs few patches applied. Please check out the
 127 `http://git.alpinelinux.org/cgit/user/tteras/strongswan/log/?h=tteras-release,release <http://git.alpinelinux.org/cgit/user/tteras/strongswan/log/?h=tteras-release,release>`_
 128 and
 129 `http://git.alpinelinux.org/cgit/user/tteras/strongswan/log/?h=tteras,working tree <http://git.alpinelinux.org/cgit/user/tteras/strongswan/log/?h=tteras,working tree>`_
 130 git repositories for the patches.
 131
 132 .. _NHRP_Events:
 133
 134 NHRP Events
 135 ===========
 136
 137 FIXME
 138
 139 Configuration Example
 140 =====================
 141
 142 FIXME
 143