Babel
Babel is a modern routing protocol designed to be robust and efficient both in ordinary wired networks and in wireless mesh networks. By default, it uses hop-count on wired networks and a variant of ETX on wireless links, It can be configured to take radio diversity into account and to automatically compute a link’s latency and include it in the metric. It is defined in RFC 8966.
Babel a dual stack protocol. A single Babel instance is able to perform routing for both IPv4 and IPv6.
General Configuration
VyOS does not have a special command to start the Babel process. The Babel process starts when the first Babel enabled interface is configured.
Optional Configuration
This command enables routing using radio frequency diversity. This is highly recommended in networks with many wireless nodes.
Note
If you enable this, you will probably want to set diversity-factor and channel below.
This command sets the multiplicative factor used for diversity routing, in units of 1/256; lower values cause diversity to play a more important role in route selection. The default it 256, which means that diversity plays no role in route selection; you will probably want to set that to 128 or less on nodes with multiple independent radios.
This command specifies the time in milliseconds after which an ‘important’ request or update will be resent. The default is 2000 ms.
This command specifies the time constant, in seconds, of the smoothing algorithm used for implementing hysteresis. Larger values reduce route oscillation at the cost of very slightly increasing convergence time. The value 0 disables hysteresis, and is suitable for wired networks. The default is 4 s.
Interfaces Configuration
This command sets the interface type:
auto – automatically determines the interface type. wired – enables optimisations for wired interfaces. wireless – disables a number of optimisations that are only correct on wired interfaces. Specifying wireless is always correct, but may cause slower convergence and extra routing traffic.
This command specifies whether to perform split-horizon on the interface. Specifying no babel split-horizon is always correct, while babel split-horizon is an optimisation that should only be used on symmetric and transitive (wired) networks.
default – enable split-horizon on wired interfaces, and disable split-horizon on wireless interfaces. enable – enable split-horizon on this interfaces. disable – disable split-horizon on this interfaces.
This command specifies the time in milliseconds between two scheduled hellos. On wired links, Babel notices a link failure within two hello intervals; on wireless links, the link quality value is reestimated at every hello interval. The default is 4000 ms.
This command specifies the time in milliseconds between two scheduled updates. Since Babel makes extensive use of triggered updates, this can be set to fairly high values on links with little packet loss. The default is 20000 ms.
This command specifies the base receive cost for this interface. For wireless interfaces, it specifies the multiplier used for computing the ETX reception cost (default 256); for wired interfaces, it specifies the cost that will be advertised to neighbours.
This command specifies the decay factor for the exponential moving average of RTT samples, in units of 1/256. Higher values discard old samples faster. The default is 42.
This command specifies the minimum RTT, in milliseconds, starting from which we increase the cost to a neighbour. The additional cost is linear in (rtt - rtt-min). The default is 10 ms.
This command specifies the maximum RTT, in milliseconds, above which we don’t increase the cost to a neighbour. The default is 120 ms.
This command specifies the maximum cost added to a neighbour because of RTT, i.e. when the RTT is higher or equal than rtt-max. The default is 150. Setting it to 0 effectively disables the use of a RTT-based cost.
This command enables sending timestamps with each Hello and IHU message in order to compute RTT values. It is recommended to enable timestamps on tunnel interfaces.
This command set the channel number that diversity routing uses for this interface (see diversity option above).
1-254 – interfaces with a channel number interfere with interfering interfaces and interfaces with the same channel number. interfering – interfering interfaces are assumed to interfere with all other channels except noninterfering channels. noninterfering – noninterfering interfaces are assumed to only interfere with themselves.
Redistribution Configuration
This command redistributes routing information from the given route source to the Babel process.
IPv4 route source: bgp, connected, eigrp, isis, kernel, nhrp, ospf, rip, static.
IPv6 route source: bgp, connected, eigrp, isis, kernel, nhrp, ospfv3, ripng, static.
This command can be used to filter the Babel routes using access lists.
in and out this is the direction in which the access
lists are applied.
This command allows you apply access lists to a chosen interface to filter the Babel routes.
This command can be used to filter the Babel routes using prefix lists.
in and out this is the direction in which the prefix
lists are applied.
Configuration Example
Simple Babel configuration using 2 nodes and redistributing connected interfaces.
Node 1:
set interfaces loopback lo address 10.1.1.1/32
set interfaces loopback lo address fd12:3456:dead:beef::1/128
set protocols babel interface eth0 type wired
set protocols babel redistribute ipv4 connected
set protocols babel redistribute ipv6 connected
Node 2:
set interfaces loopback lo address 10.2.2.2/32
set interfaces loopback lo address fd12:3456:beef:dead::2/128
set protocols babel interface eth0 type wired
set protocols babel redistribute ipv4 connected
set protocols babel redistribute ipv6 connected