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JunosE 11.3.x IP, IPv6, and IGP Configuration Guide
Overview
OSPF Terms
236
OSPF is an interior gateway protocol (IGP) that runs within a single autonomous system
(AS). Exterior gateway protocols (EGPs), such as Border Gateway Protocol (BGP),
exchange routing information between ASs.
OSPF is a link-state routing protocol, similar to the Intermediate System–to–Intermediate
System (IS-IS) routing protocol. It advertises the states of its local network links. This
link advertisement distinguishes OSPF from some IGPs, such as Routing Information
Protocol (RIP). A distance vector protocol, such as RIP, advertises the distances (that
is, the number of hops) to each known destination within the network.
Each participating OSPF router within the AS has an identical database describing the
AS's topology. Each individual piece of this database is a particular router's local state.
From this database, OSPF calculates a routing table by constructing a shortest-path
tree.
OSPF learns the best routes to reachable destinations. It can quickly detect changes in
the topology of an AS and, after a short convergence period, calculate new loop-free
routes. This protocol has been designed expressly for the TCP/IP Internet environment,
including explicit support for classless interdomain routing (CIDR) and the tagging of
externally derived routing information.
This chapter provides direction for customizing basic OSPF settings if you need to do so.
For detailed information about the OSPF commands, see the JunosE Command Reference
Guide.
Table 9 on page 236 defines commonly used OSPF terms.
Table 9: OSPF-Related Terms
Term
Meaning
adjacency
The relationship between selected neighboring routers for exchanging
routing information. Not every pair of neighboring routers is adjacent.
area
A collection of network segments interconnected by routers. It is a
region in an OSPF routing domain.
area border router
A router that sits on the edge of an OSPF area and routes link-state
(ABR)
advertisements (LSAs) between areas.
area ID
A unique number that identifies an area. Typically, formatted as an IP
address.
authentication
A process whereby a user or data source proves that it is what it claims
to be.
Copyright © 2010, Juniper Networks, Inc.
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