Ospf Default Route Preference Values; Ospf Routing Algorithm - Juniper ACX1000 Configuration Manual

ACX Series Universal Access Router Configuration Guide

OSPF Default Route Preference Values

Table 44: Default Route Preference Values for OSPF
How Route Is Learned
OSPF internal route
OSPF AS external routes

OSPF Routing Algorithm

544
NOTE: By default, Junos OS is compatible with RFC 1583, OSPF Version 2. In
Junos OS Release 8.5 and later, you can disable compatibility with RFC 1583
by including the
Disabling OSPFv2 Compatibility with RFC 1583.
This topic describes the following information:
OSPF Default Route Preference Values on page 544
OSPF Routing Algorithm on page 544
OSPF Three-Way Handshake on page 545
OSPF Version 3 on page 546
The Junos OS routing protocol process assigns a default preference value to each route
that the routing table receives. The default value depends on the source of the route.
The preference value is from 0 through 4,294,967,295 (232 – 1), with a lower value
indicating a more preferred route.
for OSPF.
Default Preference
10
150
OSPF uses the shortest-path-first (SPF) algorithm, also referred to as the Dijkstra
algorithm, to determine the route to each destination. All routing devices in an area run
this algorithm in parallel, storing the results in their individual topological databases.
Routing devices with interfaces to multiple areas run multiple copies of the algorithm.
This section provides a brief summary of how the SPF algorithm works.
When a routing device starts, it initializes OSPF and waits for indications from lower-level
protocols that the router interfaces are functional. The routing device then uses the OSPF
hello protocol to acquire neighbors, by sending hello packets to its neighbors and receiving
their hello packets.
On broadcast or nonbroadcast multiaccess networks (physical networks that support
the attachment of more than two routing devices), the OSPF hello protocol elects a
designated router for the network. This routing device is responsible for sending link-state
advertisements (LSAs) that describe the network, which reduces the amount of network
traffic and the size of the routing devices' topological databases.
The routing device then attempts to form adjacencies with some of its newly acquired
neighbors. (On multiaccess networks, only the designated router and backup designated
statement. For more information, see Example:
no-rfc-1583
Table 44 on page 544
Statement to Modify Default Preference
OSPF preference
OSPF external-preference
lists the default preference values
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