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Supported Routing Table Features
The JUNOS software maintains two databases for
routing information:
- Routing table—Contains all the routing information
learned by all routing protocols. (Some vendors refer to this kind
of table as a routing information base [RIB].)
- Forwarding table—Contains the routes actually used
to forward packets. (Some vendors refer to this kind of table as a
forwarding information base [FIB].)
By default, the JUNOS software maintains three
routing tables: one for IPv4 unicast routes, a second for multicast
routes, and a third for Multiprotocol Label Switching (MPLS). You
can configure additional routing tables.
The JUNOS software maintains separate routing tables
for IPv4 and IPv6 routes.
The JUNOS software installs all active routes from
the routing table into the forwarding table. The active routes are
routes that are used to forward packets to their destinations. The
JUNOS kernel maintains a master copy of the forwarding table. It copies
the forwarding table to the Packet Forwarding Engine, which is the
component responsible for forwarding packets.
The JUNOS routing protocol process generally determines
the active route by selecting the route with the lowest preference
value. The JUNOS software provides support for alternate and tiebreaker
preferences, and some of the routing protocols, including BGP and
MPLS, use these additional preferences.
You can add static, aggregate, and generated routes
to the JUNOS routing tables, configuring the routes with one or more
of the properties shown in Table 7.
Table 7: Routing
Table Route Properties
|
Description
|
Static
|
Aggregate
|
Generated
|
|
Destination address
|
X
|
X
|
X
|
|
Default route to the destination
|
X
|
X
|
X
|
|
IP address or interface of the next hop to the destination
|
X
|
–
|
–
|
|
LSP as next hop
|
X
|
–
|
–
|
|
Drop the packets, install a reject route for this destination,
and send ICMP unreachable messages
|
X
|
X
|
X
|
|
Drop the packets, install a reject route for this destination,
but do not send ICMP unreachable messages
|
X
|
X
|
X
|
|
Cause packets to be received by the local routing platform
|
X
|
–
|
–
|
|
Associate a metric value with the route
|
X
|
X
|
X
|
|
Type of route
|
X
|
X
|
X
|
|
Preference values
|
X
|
X
|
X
|
|
Additional preference values
|
X
|
X
|
X
|
|
Independent preference (qualified-next-hop statement)
|
X
|
–
|
–
|
|
BGP community information to associate with the route
|
X
|
X
|
X
|
|
Autonomous system (AS) path information to associate with the
route
|
X
|
X
|
X
|
|
OSPF tag strings to associate with the route
|
X
|
X
|
X
|
|
Do not install active static routes into the forwarding table
|
X
|
–
|
–
|
|
Install the route into the forwarding table
|
X
|
–
|
–
|
|
Permanently retain a static route in the forwarding table
|
X
|
–
|
–
|
|
Include only the longest common leading sequences from the contributing
AS paths
|
–
|
X
|
–
|
|
Include all AS numbers for a specific route
|
–
|
X
|
–
|
|
Retain an inactive route in the routing and forwarding tables
|
X
|
X
|
X
|
|
Remove an inactive route from the routing and forwarding tables
|
X
|
X
|
X
|
|
Active policy to associate with the route
|
–
|
X
|
X
|
|
Specify that a route is ineligible for readvertisement
|
X
|
–
|
–
|
|
Specify route to a prefix that is not a directly connected next
hop
|
X
|
–
|
–
|
You can add martian addresses to the JUNOS routing
tables.
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