Information About Implementing Ospf - Cisco NCS 6000 Series Configuration Manual

Information About Implementing OSPF

• You must be in a user group associated with a task group that includes the proper task IDs. The command
• Configuration tasks for OSPFv3 assume that you are familiar with IPv6 addressing and basic configuration.
• Before you enable OSPFv3 on an interface, you must perform the following tasks:
• Configuring authentication (IP Security) is an optional task. If you choose to configure authentication,
Information About Implementing OSPF
To implement OSPF you need to understand the following concepts:
OSPF Functional Overview
OSPF is a routing protocol for IP. It is a link-state protocol, as opposed to a distance-vector protocol. A
link-state protocol makes its routing decisions based on the states of the links that connect source and destination
machines. The state of the link is a description of that interface and its relationship to its neighboring networking
devices. The interface information includes the IP address of the interface, network mask, type of network to
which it is connected, routers connected to that network, and so on. This information is propagated in various
types of link-state advertisements (LSAs).
A router stores the collection of received LSA data in a link-state database. This database includes LSA data
for the links of the router. The contents of the database, when subjected to the Dijkstra algorithm, extract data
to create an OSPF routing table. The difference between the database and the routing table is that the database
contains a complete collection of raw data; the routing table contains a list of shortest paths to known
destinations through specific router interface ports.
OSPF is the IGP of choice because it scales to large networks. It uses areas to partition the network into more
manageable sizes and to introduce hierarchy in the network. A router is attached to one or more areas in a
network. All of the networking devices in an area maintain the same complete database information about the
link states in their area only. They do not know about all link states in the network. The agreement of the
database information among the routers in the area is called convergence.
At the intradomain level, OSPF can import routes learned using Intermediate System-to-Intermediate System
(IS-IS). OSPF routes can also be exported into IS-IS. At the interdomain level, OSPF can import routes learned
using Border Gateway Protocol (BGP). OSPF routes can be exported into BGP.
Unlike Routing Information Protocol (RIP), OSPF does not provide periodic routing updates. On becoming
neighbors, OSPF routers establish an adjacency by exchanging and synchronizing their databases. After that,
only changed routing information is propagated. Every router in an area advertises the costs and states of its
links, sending this information in an LSA. This state information is sent to all OSPF neighbors one hop away.
Routing Configuration Guide for Cisco NCS 6000 Series Routers, IOS XR Release 6.4.x
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reference guides include the task IDs required for each command. If you suspect user group assignment
is preventing you from using a command, contact your AAA administrator for assistance.
See the Implementing Network Stack IPv4 and IPv6 on module of the IP Addresses and Services
Configuration Guide for Cisco NCS 6000 Series Routers for information on IPv6 routing and addressing.
• Complete the OSPF network strategy and planning for your IPv6 network. For example, you must
decide whether multiple areas are required.
• Enable IPv6 on the interface.
you must first decide whether to configure plain text or Message Digest 5 (MD5) authentication, and
whether the authentication applies to an entire area or specific interfaces.
Implementing OSPF