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.
Optional configuration
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.
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.
Configure the delay in milliseconds before the system resends an important request or update.
The default value is 2000 ms.
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
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.
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.
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.
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.
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.
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.
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.
Configure the maximum RTT, in milliseconds, above which the cost to a neighbor stops increasing.
The default value is 120 ms.
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.
Configure adding timestamps to each Hello and IHU message to calculate RTT values.
Enabling timestamps is recommended for tunnel interfaces.
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 asinterfering.interfering: The interface interferes with all others except those configured asnoninterfering.noninterfering: The interface interferes only with itself.
Redistribution configuration
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,staticipv6:
bgp,connected,eigrp,isis,kernel,nhrp,ospfv3,ripng,static
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.
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.
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.
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:
# 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:
# 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