Rib And Fib Routing Tables; Administrative Distance - Allied Telesis SwitchBlade x908 Series Software Reference Manual

Route Selection

RIB and FIB Routing Tables

Your device maintains its routing information in routing tables that tell your device how to find
a remote network or host. Each route is uniquely identified in a table by its IP address, network
mask, next hop, interface, protocol, and policy. There are two routing tables populated by your
device: the Routing Information Base (RIB) and the Forwarding Information Base (FIB).
Routing The RIB records all the routes that your device has learnt. Your device uses the RIB to
Information Base advertise routes to its neighbor devices and to populate the FIB. It adds routes to this table
when:
■
■
■
■
Forwarding The RIB populates the Forwarding Information Base (FIB) with the best route to each
Information Base destination. When your device receives an IP packet, and no filters are active that would
exclude the packet, it uses the FIB to find the most specific route to the destination. If your
device does not find a direct route to the destination, and no default route exists, it discards the
packet and sends an ICMP message to that effect back to the source.
Adjusting table To view the routes in the RIB, use the command:
entries
To view the routes in the FIB, use the command:

Administrative Distance

When multiple routes are available for the same prefix, the AlliedWare Plus
routes with the lowest administrative distance to the FIB. The administrative distance is a rank
given to a route based on the protocol that the route was received from. The lower the
administrative distance, the higher the route preference. For example, if the RIB has these
routes
Route
1
2
3
then the AlliedWare Plus
has a higher administrative distance than a route with the same prefix.
29.4
you add a static route using the
one or more routing protocols, such as RIP or OSPF, exchanges routing information with
other routers or hosts
your device receives route information from a connected interface
your device gathers route information from an ICMP redirect message or DHCP message
awplus#show ip route database [bgp|connected|ospf|rip|static]
awplus# show ip route [bgp|connected|ospf|rip|static|<ip-address>|<ip-address/m>]
Prefix
192.168.0/16
192.168.0/16
192.168.1/24
TM
OS adds routes 1 and 3 to the FIB. It does not add route 2, as this
Software Reference for SwitchBlade® x908, x900 and x600 Series Switches
TM
AlliedWare Plus Operating System - Software Version 5.3.1
ip route command
Protocol
eBGP
OSPF
OSPF
TM
OS adds the
Distance
20
110
110
C613-50007-01 REV B