Manual:Interface/HWMPplus

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Prerequisites for this article: you understand what WDS is and why to use it

Overview

HWMP+ is a MikroTik specific layer-2 routing protocol for wireless mesh networks. It is based on Hybrid Wireless Mesh Protocol (HWMP) from IEEE 802.11s draft standard. It can be used instead of (Rapid) Spanning Tree protocols in mesh setups to ensure loop-free optimal routing.

The HWMP+ protocol however is not compatible with HWMP from the proposed IEEE 802.11s standard.

Note that the distribution system you use for your network need not to be Wireless Distribution System (WDS). HWMP+ mesh routing supports not only WDS interfaces, but also Ethernet interfaces inside the mesh. So you can use simple Ethernet based distribution system, or you can combine both WDS and Ethernet links!

Configuration

/interface mesh

Configure mesh interface.

admin-mac (MAC address, default: 00:00:00:00:00:00) -- administratively assigned MAC address, used when auto-mac setting is disabled

arp (disabled | enabled | proxy-arp | reply-only; default: enabled) - address resolution protocol setting

auto-mac (boolean, default: no) -- if disabled, then value from admin-mac will be used as the MAC address of the mesh interface; else address of some port will be used if ports are present

hwmp-default-hoplimit (integer: 1..255) -- maximum hop count for generated routing protocol packets; after a HWMP+ packet is forwarded "hoplimit" times, it is dropped

hwmp-prep-lifetime (time, default: 5m) -- lifetime for routes created from received PREP or PREQ messages

hwmp-preq-destination-only (boolean, default: yes) -- whether only destination can respond to HWMP+ PREQ message

hwmp-preq-reply-and-forward (boolean, default: yes) -- whether intermediate nodes should forward HWMP+ PREQ message after responding to it. Useful only when hwmp-preq-destination-only is disabled

hwmp-preq-retries (integer, default: 2) -- how much times to retry route discovery to a specific MAC address before the address is considered unreachable

hwmp-preq-waiting-time (time, default: 4s) -- how long to wait for a response to the first PREQ message. Note that for subsequent PREQs the waiting time is increased exponentially

hwmp-rann-interval (time, default: 10s) -- how often to send out HWMP+ RANN messages

hwmp-rann-lifetime (time, default: 1s) -- lifetime for routes created from received RANN messages

hwmp-rann-propagation-delay (number, default: 50) -- how long to wait before propagating a RANN message. Value in centiseconds (100cs = 1sec)

mesh-portal (boolean, default: no) -- whether this interface is a portal in the mesh network

mtu (number, default: 1500) -- maximum transmit units

name (string) -- interface name

reoptimize-paths (boolean, default: no) -- whether to send out periodic PREQ messages asking for known MAC addresses. Turing on this setting is useful if network topology is often changing. Note that if no reply is received to a reoptimization PREQ, the existing path is kept anyway (until it timeouts itself)

/interface mesh port

Configure mesh interface ports.

hello-interval (time, default: 10s) -- maximum interval between sending out HWMP+ Hello messages. Used only for Ethernet type ports

interface (interface name) -- interface name, which is to be included in a mesh

mesh (interface name) -- mesh interface this port belongs to

path-cost (integer: 0..65535; default: 10) -- path cost to the interface, used by routing protocol to determine the 'best' path

port-type (WDS | auto | ethernet | wireless) -- port type to use

  • auto - port type is determined automatically based on the underlying interface's type
  • WDS - a Wireless Distribution System interface, kind of point-to-point wireless link. Remote MAC address is known from wireless connection data
  • ethernet - Remote MAC addresses are learned either from HWMP+ Hello messages or from source MAC addresses in received or forwarded traffic
  • wireless - Remote MAC addresses are known from wireless connection data

port-type-used (read-only, wireless | WDS | ethernet-mesh | ethernet-bridge | ethernet-mixed) -- port type and state actually used

/interface mesh fdb

Read-only status of the mesh interface Forwarding Database (FDB).

mac-address (MAC address) -- MAC address corresponding for this FDB entry

seqnum (integer) -- sequence number used in routing protocol to avoid loops

type (local | outsider | direct | mesh | neighbor | larval | unknown) -- type of this FDB entry

  • local -- MAC address belongs to the local router itself
  • outsider -- MAC address belongs to a device external to the mesh network
  • direct -- MAC address belongs to a wireless client on an interface that is in the mesh network
  • mesh -- MAC address belongs to a device reachable over the mesh network; it can be either internal or external to the mesh network
  • neighbor -- MAC address belongs to a mesh router that is direct neighbor to this router
  • larval -- MAC address belongs to an unknown device that is reachable over the mesh network
  • unknown -- MAC address belongs to an unknown device

mesh (interface name) -- the mesh interface this FDB entry belongs to

on-interface (interface name) -- mesh port used for traffic forwarding, kind of a next-hop value

lifetime (time) -- time remaining to live if this entry is not used for traffic forwarding

age (time) -- age of this FDB entry

metric (integer) -- metric value used by routing protocol to determine the 'best' path

Additional wireless configuration

Use wds-default-cost and wds-cost-range wireless interface parameters for controlling the metric that is used in the routing protocol. The WDS cost will be used as path-cost for ports dynamically added to the mesh interface.

Example (there will be images soon)

    B
  /   \
 /     \
A       C
 \     /
  \   /
    D

This example uses static WDS links that are dynamically added as mesh ports when they become active. Two different frequencies are used: one for AP interconnections, and one for client connections to APs, so the AP must have at least two wireless interfaces.

Repeat this configuration on all APs:

/interface mesh add disabled=no
/interface mesh port add interface=wlan1 mesh=mesh1
/interface mesh port add interface=wlan2 mesh=mesh1
# interface used for AP interconnections 
/interface wireless set wlan1 disabled=no ssid=mesh frequency=2437 band=2.4ghz-b/g mode=ap-bridge wds-mode=static-mesh wds-default-bridge=mesh1
# interface used for client connections
/interface wireless set wlan2 disabled=no ssid=mesh-clients frequency=5180 band=5ghz mode=ap-bridge 
# a static WDS interface for each AP you want to connect to
/interface wireless wds add disabled=no master-interface=wlan1 name=<descriptive name of remote end> wds-address=<MAC address of remote end>

In real world setups you also should take care of securing the wireless connections, using /interface wireless security-profile. For simplicity that configuration it's not shown here.

Results on router A (there is one client is connected to wlan2):

[admin@A] > /interface mesh pr
Flags: X - disabled, R - running
 0  R name="mesh1" mtu=1500 arp=enabled mac-address=00:0C:42:0C:B5:A4 auto-mac=yes
      admin-mac=00:00:00:00:00:00 mesh-portal=no hwmp-default-hoplimit=32
      hwmp-preq-waiting-time=4s hwmp-preq-retries=2 hwmp-preq-destination-only=yes
      hwmp-preq-reply-and-forward=yes hwmp-prep-lifetime=5m hwmp-rann-interval=10s
      hwmp-rann-propagation-delay=1s hwmp-rann-lifetime=22s
[admin@A] > interface mesh port p detail
Flags: X - disabled, I - inactive, D - dynamic
 0    interface=wlan1 mesh=mesh1 path-cost=10 hello-interval=10s port-type=auto port-type-used=wireless
 1    interface=wlan2 mesh=mesh1 path-cost=10 hello-interval=10s port-type=auto port-type-used=wireless
 2  D interface=router_B mesh=mesh1 path-cost=105 hello-interval=10s port-type=auto port-type-used=WDS
 3  D interface=router_D mesh=mesh1 path-cost=76 hello-interval=10s port-type=auto port-type-used=WDS
[admin@A] /interface mesh> fdb print
Flags: A - active, R - root
   MESH        TYPE     MAC-ADDRESS       ON-INTERFACE       LIFETIME     AGE
A  mesh1       local    00:0C:42:00:00:AA                                 3m17s
A  mesh1       neighbor 00:0C:42:00:00:BB router_B                        1m2s
A  mesh1       neighbor 00:0C:42:00:00:DD router_D                        3m16s
A  mesh1       direct   00:0C:42:0C:7A:2B wlan2                           2m56s
A  mesh1       local    00:0C:42:0C:B5:A4                                 2m56s
[admin@A] /interface mesh> fdb print detail
Flags: A - active, R - root
 A  mac-address=00:0C:42:00:00:AA type=local age=3m21s mesh=mesh1 metric=0
     seqnum=4294967196
 A  mac-address=00:0C:42:00:00:BB type=neighbor on-interface=router_B age=1m6s
    mesh=mesh1 metric=132 seqnum=4294967196
 A  mac-address=00:0C:42:00:00:DD type=neighbor on-interface=router_D age=3m20s
     mesh=mesh1 metric=79 seqnum=4294967196
 A  mac-address=00:0C:42:0C:7A:2B type=direct on-interface=wlan2 age=3m mesh=mesh1
     metric=10 seqnum=0
 A  mac-address=00:0C:42:0C:B5:A4 type=local age=3m mesh=mesh1 metric=0 seqnum=0

Test that ping works:

[admin@A] > /ping 00:0C:42:00:00:CC
00:0C:42:00:00:CC 64 byte ping time=108 ms
00:0C:42:00:00:CC 64 byte ping time=51 ms
00:0C:42:00:00:CC 64 byte ping time=39 ms
00:0C:42:00:00:CC 64 byte ping time=43 ms
4 packets transmitted, 4 packets received, 0% packet loss
round-trip min/avg/max = 39/60.2/108 ms

Also test that ARP resolving works and so does IP level ping:

[admin@A] > /ping 10.4.0.3
10.4.0.3 64 byte ping: ttl=64 time=163 ms
10.4.0.3 64 byte ping: ttl=64 time=46 ms
10.4.0.3 64 byte ping: ttl=64 time=48 ms
3 packets transmitted, 3 packets received, 0% packet loss
round-trip min/avg/max = 46/85.6/163 ms


Advanced topics

We all know that it's easy to make problematic layer-2 bridging or routing setups and hard to debug them. (Compared to layer-3 routing setups.) So there are a few bad configuration examples which could create problems for you. Avoid them!

Problematic example 1: Ethernet switch inside a mesh

a === [switch] === B --- C
         #
         #
         D

A will not be able to communicate reliably with C. The problem manifests itself when D is the designated router for Ethernet; if B takes this role, everything is OK. In short, reason of the problem is MAC address learning on switch.

Consider what happens when router A wants to send something to C. We suppose router A either knowns or floods data to all interfaces. Either way, data arrives at switch. The switch, not knowing anything about destination's MAC address, forwards to data both to B and D.

What happens now:

  1. B receives the packet on a mesh interface. Since the MAC address is not local for B, and B knows that he is not the designated router for Network1, he simply ignores the packet.
  2. D receives the packet on a mesh interface. Since the MAC address is not local for B, and D is the designated router for Network1, he initiates path discovery process to C.

After path discovery is completed, D has information that C is reachable over B. Now D encapsulates the packet and forwards back to Network1. The encapsulated packet forwarded by switch, received and forwarded by B, and received by C. So far everything is good.

Now C is likely to respond to the packet. Since B already knows where A is, he will decapsulate and forward the packet. But now switch will learn that the MAC address of C is reachable through B! That means, next time when something arrives from A addressed to C, the switch will forward data only to B. (And B, of course, will silently ignore the packet).

In contrast, if B took up the role of designated router, everything would be OK, because traffic would not have to cross Network1 twice.

Troubleshooting: either avoid such setup or disable MAC address learning on the switch. Note that it's not possible on many switches.

Problematic example 2: wireless modes

Consider this setup (invalid):

AP -- WDS -- (wlan1) AP/S (wlan2) -- AP

It is not possible to bridge wlan1 and wlan2 on Node2 now. The reason for this is pretty obvious if you understand how WDS works. For WDS communications four address frames are used. This is because for wireless multihop forwarding you need to know both the addresses of intermediate hops, as well as the original sender and final receiver. In contrast, non-WDS 802.11 communication includes only three MAC addresses in a frame. That's why it's not possible to do multihop forwarding in station mode.

Troubleshooting: depends on what you want to achieve:

  1. If you want to Node3 as a repeater either for wireless or Ethernet traffic, configure WDS link between Node2 and Node3, and run mesh routing protocol on all nodes.
  2. In other cases configure wlan2 on Node2 in AP mode, and wlan on Node3 in station mode.