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+```{eval-rst}
+.. meta::
+   :description: The Babel routing protocol provides robust and efficient
+                 routing for wired and wireless mesh networks.
+   :keywords: babel, routing, protocol, wireless, mesh, network, metric,
+              ipv4, ipv6
+```
+
+(babel)=
+
+# Babel
+
+The Babel protocol provides robust and efficient routing for both wired and
+wireless mesh networks. By default, Babel uses hop-count metrics on wired links
+and a variant of Expected Transmission Count (ETX) on wireless links.
+Administrators can configure Babel to account for radio diversity,
+automatically compute link latency, and include that latency in the routing
+metric. {rfc}`8966` defines the Babel protocol.
+
+Babel is a dual-stack protocol. A single Babel instance routes both IPv4 and
+IPv6 traffic simultaneously.
+
+## General configuration
+
+VyOS does not require a specific command to start the Babel process. The system
+automatically starts the routing process when you configure the first
+Babel-enabled interface.
+
+```{cfgcmd} set protocols babel interface \<interface\>
+
+**Enable Babel routing on the specified interface.**
+
+The system immediately begins sending and receiving Babel packets on this
+interface.
+```
+
+## Optional configuration
+
+```{cfgcmd} set protocols babel parameters diversity
+
+**Enable radio-frequency diversity routing for the Babel process.**
+
+Enabling this feature is highly recommended for networks with many
+wireless nodes.
+
+:::{note}
+When you enable diversity routing, you should also configure the
+``diversity-factor`` and ``channel`` parameters.
+:::
+```
+
+```{cfgcmd} set protocols babel parameters diversity-factor \<1-256\>
+
+**Configure the multiplicative factor for diversity routing, in units of
+1/256.**
+
+Lower multiplicative factors give greater weight to diversity in route
+selection. The default value is 256, which disables diversity routing.
+On nodes with multiple independent radios, configure a value of 128 or less.
+```
+
+```{cfgcmd} set protocols babel parameters resend-delay \<20-655340\>
+
+**Configure the delay in milliseconds before the system resends an
+important request or update.**
+
+The default value is 2000 ms.
+```
+
+```{cfgcmd} set protocols babel parameters smoothing-half-life \<0-65534\>
+
+**Configure the time constant, in seconds, for the smoothing algorithm used
+to implement hysteresis.**
+
+Higher values reduce route oscillation but slightly increase convergence
+time. A value of 0 disables hysteresis and is suitable for wired networks.
+The default is 4 seconds.
+```
+
+## Interfaces configuration
+
+```{cfgcmd} set protocols babel interface \<interface\> type \<auto|wired|wireless\>
+
+**Configure the network type for the Babel-enabled interface.**
+
+Choose from the following:
+
+* ``auto``: Babel automatically detects if an interface is wired or
+  wireless.
+* ``wired``: Babel enables optimizations for wired interfaces.
+* ``wireless``: Babel disables optimizations suitable only for wired
+  interfaces. Specifying wireless is always correct, but may cause slower
+  convergence and increased routing traffic.
+```
+
+```{cfgcmd} set protocols babel interface \<interface\> split-horizon \<default|disable|enable\>
+
+**Configure the split-horizon routing behavior for the specified
+interface.**
+
+Use one of the following options:
+
+* ``default``: Babel automatically enables split-horizon on wired
+  interfaces and disables it on wireless interfaces.
+* ``enable``: Babel enables split-horizon on the interface. This
+  optimization should be used only on symmetric, transitive (wired)
+  networks.
+* ``disable``: Babel disables split-horizon on the interface. Disabling
+  split-horizon is always safe and correct.
+```
+
+```{cfgcmd} set protocols babel interface \<interface\> hello-interval \<20-655340\>
+
+**Configure the interval, in milliseconds, between scheduled hello messages
+on the specified interface.**
+
+On wired links, Babel detects link failures within two hello intervals.
+On wireless links, link quality is reestimated at each interval. The
+default is 4000 ms.
+```
+
+```{cfgcmd} set protocols babel interface \<interface\> update-interval \<20-655340\>
+
+**Configure the interval, in milliseconds, between scheduled routing
+updates on the specified interface.**
+
+Because Babel uses triggered updates extensively, you can increase this
+value on reliable links with minimal packet loss. The default is 20000 ms.
+```
+
+```{cfgcmd} set protocols babel interface \<interface\> rxcost \<1-65534\>
+
+**Configure the base receive cost for the specified interface.**
+
+Babel applies this value based on the configured network type:
+
+* ``wired``: The value is the routing cost advertised to neighboring
+  routers.
+* ``wireless``: The value is a multiplier used to compute the ETX
+  (Expected Transmission Count) reception cost.
+
+The default value is 256.
+```
+
+```{cfgcmd} set protocols babel interface \<interface\> rtt-decay \<1-256\>
+
+**Configure the decay factor for the exponential moving average of RTT
+samples, in units of 1/256.**
+
+Higher values discard older samples faster. The default value is 42.
+```
+
+```{cfgcmd} set protocols babel interface \<interface\> rtt-min \<1-65535\>
+
+**Configure the minimum RTT, in milliseconds, at which the cost to a
+neighbor begins to increase.**
+
+The additional cost is linear in (rtt - rtt-min). The default value is 10 ms.
+```
+
+```{cfgcmd} set protocols babel interface \<interface\> rtt-max \<1-65535\>
+
+**Configure the maximum RTT, in milliseconds, above which the cost to a
+neighbor stops increasing.**
+
+The default value is 120 ms.
+```
+
+```{cfgcmd} set protocols babel interface \<interface\> max-rtt-penalty \<0-65535\>
+
+**Configure the maximum cost added to a neighbor when RTT meets or exceeds
+rtt-max.**
+
+Setting this value to 0 disables RTT-based costs. The default value is 150.
+```
+
+```{cfgcmd} set protocols babel interface \<interface\> enable-timestamps
+
+**Configure adding timestamps to each Hello and IHU message to calculate
+RTT values.**
+
+Enabling timestamps is recommended for tunnel interfaces.
+```
+
+```{cfgcmd} set protocols babel interface \<interface\> channel \<1-254|interfering|noninterfering\>
+
+**Configure the channel identifier that diversity routing uses for the
+specified interface.**
+
+Interfaces interfere with each other based on the assigned channel
+identifier:
+
+* ``1–254``: The interface interferes with interfaces sharing the same
+  channel number and with interfaces configured as ``interfering``.
+* ``interfering``: The interface interferes with all others except those
+  configured as ``noninterfering``.
+* ``noninterfering``: The interface interferes only with itself.
+```
+
+## Redistribution configuration
+
+```{cfgcmd} set protocols babel redistribute \<ipv4|ipv6\> \<route source\>
+
+**Configure the redistribution of routing information from the specified
+route source into the Babel process.**
+
+The following route sources are available:
+
+* **ipv4:** ``bgp``, ``connected``, ``eigrp``, ``isis``, ``kernel``,
+  ``nhrp``, ``ospf``, ``rip``, ``static``
+* **ipv6:** ``bgp``, ``connected``, ``eigrp``, ``isis``, ``kernel``,
+  ``nhrp``, ``ospfv3``, ``ripng``, ``static``
+```
+
+```{cfgcmd} set protocols babel distribute-list \<ipv4|ipv6\> access-list \<in|out\> \<number\>
+
+**Configure global Babel route filtering using an access list.**
+
+Specify the direction in which the access list is applied:
+
+* ``in``: Filters incoming routes.
+* ``out``: Filters outgoing routes.
+```
+
+```{cfgcmd} set protocols babel distribute-list \<ipv4|ipv6\> interface \<interface\> access-list \<in|out\> \<number\>
+
+**Configure Babel route filtering on the specified interface using an
+access list.**
+
+Specify the direction in which the access list is applied:
+
+* ``in``: Filters incoming routes.
+* ``out``: Filters outgoing routes.
+```
+
+```{cfgcmd} set protocols babel distribute-list \<ipv4|ipv6\> prefix-list \<in|out\> \<name\>
+
+**Configure global Babel route filtering using a prefix list.**
+
+Specify the direction in which the prefix list is applied:
+
+* ``in``: Filters incoming routes.
+* ``out``: Filters outgoing routes.
+```
+
+```{cfgcmd} set protocols babel distribute-list \<ipv4|ipv6\> interface \<interface\> prefix-list \<in|out\> \<name\>
+
+**Configure Babel route filtering on the specified interface using a
+prefix list.**
+
+Specify the direction in which the prefix list is applied:
+
+* ``in``: Filters incoming routes.
+* ``out``: Filters outgoing routes.
+```
+
+## Configuration example
+
+### Basic two-node babel network
+
+**Goal:** The following example connects two routers (Node 1 and Node 2) via
+their eth0 interfaces and uses the Babel routing protocol to advertise
+(redistribute) each router's locally configured networks (represented by
+loopback addresses) to one another.
+
+**Node 1:**
+
+```none
+# Configure the loopback (local networks) and physical (eth0) addresses
+set interfaces loopback lo address 10.1.1.1/32
+set interfaces loopback lo address fd12:3456:dead:beef::1/128
+set interfaces ethernet eth0 address 192.168.1.1/24
+
+# Enable Babel on the physical link
+set protocols babel interface eth0 type wired
+
+# Instruct Babel to advertise (redistribute) the locally configured networks
+set protocols babel redistribute ipv4 connected
+set protocols babel redistribute ipv6 connected
+```
+
+**Node 2:**
+
+```none
+# Configure the loopback (local networks) and physical (eth0) addresses
+set interfaces loopback lo address 10.2.2.2/32
+set interfaces loopback lo address fd12:3456:beef:dead::2/128
+set interfaces ethernet eth0 address 192.168.1.2/24
+
+# Enable Babel on the physical link
+set protocols babel interface eth0 type wired
+
+# Tell Babel to advertise (redistribute) the locally configured networks
+set protocols babel redistribute ipv4 connected
+set protocols babel redistribute ipv6 connected
+```