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Table Of Contents
Configuring OSPF Interface Parameters
Configuring OSPF over Different Physical Networks
Configuring Your OSPF Network Type
Configuring Point-to-Multipoint, Broadcast Networks
Configuring OSPF for Nonbroadcast Networks
Configuring OSPF Area Parameters
Configuring Route Summarization Between OSPF Areas
Configuring Route Summarization When Redistributing Routes into OSPF
Configuring Lookup of DNS Names
Forcing the Router ID Choice with a Loopback Interface
Changing the OSPF Administrative Distances
Configuring OSPF on Simplex Ethernet Interfaces
Configuring Route Calculation Timers
Configuring OSPF over On-Demand Circuits
Logging Neighbors Going Up or Down
LSA Group Pacing With Multiple Timers
Displaying OSPF Update Packet Pacing
Monitoring and Maintaining OSPF
OSPF Point-to-Multipoint Example
OSPF Point-to-Multipoint, Broadcast Example
OSPF Point-to-Multipoint, Nonbroadcast Example
Variable-Length Subnet Masks Example
OSPF Routing and Route Redistribution Examples
Basic OSPF Configuration Examples
Basic OSPF Configuration Example for Internal Router, ABR, and ASBRs
Complex Internal Router, ABR, and ASBRs Example
Complex OSPF Configuration for ABR Examples
Changing OSPF Administrative Distance Example
OSPF over On-Demand Routing Example
Ignore MOSPF LSA Packets Example
Configuring OSPF
This chapter describes how to configure Open Shortest Path First (OSPF). For a complete description of the OSPF commands in this chapter, refer to the "OSPF Commands" module in the Cisco IOS IP Routing Protocols Command Reference. To locate documentation of other commands that appear in this chapter, use the command reference master index, or search online.
OSPF is an Interior Gateway Protocol (IGP) developed by the OSPF working group of the Internet Engineering Task Force (IETF). Designed expressly for IP networks, OSPF supports IP subnetting and tagging of externally derived routing information. OSPF also allows packet authentication and uses IP multicast when sending and receiving packets.
We support RFC 1253, Open Shortest Path First (OSPF) MIB, August 1991. The OSPF MIB defines an IP routing protocol that provides management information related to OSPF and is supported by Cisco routers.
For protocol-independent features that work with OSPF, see the "Configuring IP Routing Protocol-Independent Features" module.
Finding Support Information for Platforms and Cisco IOS and Catalyst OS Software Images
Use Cisco Feature Navigator to find information about platform support and Cisco IOS and Catalyst OS software image support. To access Cisco Feature Navigator, go to http://www.cisco.com/go/cfn. An account on Cisco.com is not required.
The Cisco OSPF Implementation
The Cisco implementation conforms to the OSPF Version 2 specifications detailed in the Internet RFC 2328. The list that follows outlines key features supported in the Cisco OSPF implementation:
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Stub areas—Definition of stub areas is supported.
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OSPF Configuration Task List
OSPF typically requires coordination among many internal routers: Area Border Routers (ABRs), which are routers connected to multiple areas, and Autonomous System Boundary Routers (ASBRs). At a minimum, OSPF-based routers or access servers can be configured with all default parameter values, no authentication, and interfaces assigned to areas. If you intend to customize your environment, you must ensure coordinated configurations of all routers.
In addition, you can specify route redistribution; see the task "Redistribute Routing Information" in the chapter "Configuring IP Routing Protocol-Independent Features" for information on how to configure route redistribution.
To configure OSPF, perform the tasks described in the following sections. The tasks in the first section are required; the tasks in the remaining sections are optional, but might be required for your application. For information about the maximum number of interfaces, see the "Configuration Limits" section.
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Enabling OSPF
As with other routing protocols, enabling OSPF requires that you create an OSPF routing process, specify the range of IP addresses to be associated with the routing process, and assign area IDs to be associated with that range of IP addresses. To do so, use the following commands beginning in global configuration mode:
Configuring OSPF Interface Parameters
Our OSPF implementation allows you to alter certain interface-specific OSPF parameters, as needed. You are not required to alter any of these parameters, but some interface parameters must be consistent across all routers in an attached network. Those parameters are controlled by the ip ospf hello-interval, ip ospf dead-interval, and ip ospf authentication-key interface configuration commands. Therefore, be sure that if you do configure any of these parameters, the configurations for all routers on your network have compatible values.
To specify interface parameters for your network, use the following commands in interface configuration mode, as needed:
Configuring OSPF over Different Physical Networks
OSPF classifies different media into the following three types of networks by default:
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You can configure your network as either a broadcast or an NBMA network.
X.25 and Frame Relay provide an optional broadcast capability that can be configured in the map to allow OSPF to run as a broadcast network. Refer to the x25 map and frame-relay map command descriptions in the Cisco IOS Wide-Area Networking Command Reference publication for more detail.
Configuring Your OSPF Network Type
You have the choice of configuring your OSPF network type as either broadcast or NBMA, regardless of the default media type. Using this feature, you can configure broadcast networks as NBMA networks when, for example, you have routers in your network that do not support multicast addressing. You also can configure NBMA networks (such as X.25, Frame Relay, and SMDS) as broadcast networks. This feature saves you from needing to configure neighbors, as described in the section "Configuring OSPF for Nonbroadcast Networks" later in this chapter.
Configuring NBMA, multiaccess networks as either broadcast or nonbroadcast assumes that there are virtual circuits (VCs) from every router to every router or fully meshed network. This is not true for some cases, for example, because of cost constraints, or when you have only a partially meshed network. In these cases, you can configure the OSPF network type as a point-to-multipoint network. Routing between two routers not directly connected will go through the router that has VCs to both routers. Note that you need not configure neighbors when using this feature.
An OSPF point-to-multipoint interface is defined as a numbered point-to-point interface having one or more neighbors. It creates multiple host routes. An OSPF point-to-multipoint network has the following benefits compared to NBMA and point-to-point networks:
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To configure your OSPF network type, use the following command in interface configuration mode:
Router(config-if)# ip ospf network {broadcast | non-broadcast | {point-to-multipoint [non-broadcast] | point-to-point}}
Configures the OSPF network type for a specified interface.
See the "OSPF Point-to-Multipoint Example" section at the end of this chapter for an example of an OSPF point-to-multipoint network.
Configuring Point-to-Multipoint, Broadcast Networks
On point-to-multipoint, broadcast networks, there is no need to specify neighbors. However, you can specify neighbors with the neighbor router configuration command, in which case you should specify a cost to that neighbor.
Before the point-to-multipoint keyword was added to the ip ospf network interface configuration command, some OSPF point-to-multipoint protocol traffic was treated as multicast traffic. Therefore, the neighbor router configuration command was not needed for point-to-multipoint interfaces because multicast took care of the traffic. Hello, update, and acknowledgment messages were sent using multicast. In particular, multicast hello messages discovered all neighbors dynamically.
On any point-to-multipoint interface (broadcast or not), the Cisco IOS software assumed that the cost to each neighbor was equal. The cost was configured with the ip ospf cost interface confutation command. In reality, the bandwidth to each neighbor is different, so the cost should differ. With this feature, you can configure a separate cost to each neighbor. This feature applies to point-to-multipoint interfaces only.
To treat an interface as point-to-multipoint broadcast and assign a cost to each neighbor, use the following commands beginning in interface configuration mode:
Repeat Step 4 for each neighbor if you want to specify a cost. Otherwise, neighbors will assume the cost of the interface, based on the ip ospf cost interface configuration command.
Configuring OSPF for Nonbroadcast Networks
Because many routers might be attached to an OSPF network, a designated router is selected for the network. Special configuration parameters are needed in the designated router selection if broadcast capability is not configured.
These parameters need only be configured in those devices that are themselves eligible to become the designated router or backup designated router (in other words, routers with a nonzero router priority value).
To configure routers that interconnect to nonbroadcast networks, use the following command in router configuration mode:
Router(config-router)# neighbor ip-address [priority number] [poll-interval seconds]
Configures a router interconnecting to nonbroadcast networks.
You can specify the following neighbor parameters, as required:
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On point-to-multipoint, nonbroadcast networks, you now use the neighbor router configuration command to identify neighbors. Assigning a cost to a neighbor is optional.
Prior to Cisco IOS Release 12.0, some customers were using point-to-multipoint on nonbroadcast media (such as classic IP over ATM), so their routers could not dynamically discover their neighbors. This feature allows the neighbor router configuration command to be used on point-to-multipoint interfaces.
On any point-to-multipoint interface (broadcast or not), the Cisco IOS software assumed the cost to each neighbor was equal. The cost was configured with the ip ospf cost interface configuration command. In reality, the bandwidth to each neighbor is different, so the cost should differ. With this feature, you can configure a separate cost to each neighbor. This feature applies to point-to-multipoint interfaces only.
To treat the interface as point-to-multipoint when the media does not support broadcast, use the following commands beginning in interface configuration mode:
Repeat Step 4 for each neighbor if you want to specify a cost. Otherwise, neighbors will assume the cost of the interface, based on the ip ospf cost interface configuration command.
Configuring OSPF Area Parameters
Our OSPF software allows you to configure several area parameters. These area parameters, shown in the following task table, include authentication, defining stub areas, and assigning specific costs to the default summary route. Authentication allows password-based protection against unauthorized access to an area.
Stub areas are areas into which information on external routes is not sent. Instead, there is a default external route generated by the ABR, into the stub area for destinations outside the autonomous system. To take advantage of the OSPF stub area support, default routing must be used in the stub area. To further reduce the number of LSAs sent into a stub area, you can configure the no-summary keyword of the area stub router configuration command on the ABR to prevent it from sending summary link advertisement (LSAs Type 3) into the stub area.
To specify an area parameter for your network, use the following commands in router configuration mode as needed:
Configuring OSPF NSSA
The OSPF not-so-stubby area (NSSA) feature is described by RFC 1587 and was first integrated into Cisco IOS Release 11.2. OSPF NSSA is a nonproprietary extension of the existing OSPF stub area feature.
Use NSSA to simplify administration if you are an Internet service provider (ISP) or a network administrator that must connect a central site that is using OSPF to a remote site that is using a different routing protocol.
Prior to NSSA, the connection between the corporate site border router and the remote router could not be run as an OSPF stub area because routes for the remote site could not be redistributed into the stub area, and two routing protocols needed to be maintained. A simple protocol such as RIP was usually run and handled the redistribution. With NSSA, you can extend OSPF to cover the remote connection by defining the area between the corporate router and the remote router as an NSSA.
As with OSPF stub areas, NSSA areas cannot be injected with distributed routes via Type 5 LSAs. Route redistribution into an NSSA area is possible only with a special type of link-state advertisement (LSA) that is known as Type 7 that can exist only in an NSSA area. An NSSA autonomous system boundary router (ASBR) generates the Type 7 LSA so that the routes can be redistributed, and an NSSA area border router (ABR) translates the Type 7 LSA into a Type 5 LSA, which can be flooded throughout the whole OSPF routing domain. Summarization and filtering are supported during the translation.
Figure 1 shows a network diagram in which OSPF Area 1 is defined as the stub area. The EIGRP routes cannot be propagated into the OSPF domain because routing redistribution is not allowed in the stub area. However, once OSPF Area 1 is defined as an NSSA, an NSSA ASBR can inject the EIGRP routes into the OSPF NSSA by creating Type 7 LSAs.
Figure 1 OSPF NSSA
The redistributed routes from the RIP router will not be allowed into OSPF Area 1 because NSSA is an extension to the stub area. The stub area characteristics will still exist, including the exclusion of Type 5 LSAs.
To specify area parameters as needed to configure OSPF NSSA, use the following command in router configuration mode:
Router(config-router)# area area-id nssa [no-redistribution] [default-information-originate]
Defines an area to be an NSSA.
To control summarization and filtering of Type 7 LSAs into Type 5 LSAs, use the following command in router configuration mode on the ASBR:
Router(config-router)# summary address prefix mask [not advertise] [tag tag]
Controls the summarization and filtering during the translation.
Implementation Considerations
Evaluate the following considerations before you implement this feature:
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Configuring Route Summarization Between OSPF Areas
Route summarization is the consolidation of advertised addresses. This feature causes a single summary route to be advertised to other areas by an ABR. In OSPF, an ABR will advertise networks in one area into another area. If the network numbers in an area are assigned in a way such that they are contiguous, you can configure the ABR to advertise a summary route that covers all the individual networks within the area that fall into the specified range.
To specify an address range, use the following command in router configuration mode:
Router(config-router)# area area-id range ip-address mask [advertise | not-advertise][cost cost]
Specifies an address range for which a single route will be advertised.
Configuring Route Summarization When Redistributing Routes into OSPF
When routes from other protocols are redistributed into OSPF (as described in the chapter "Configuring IP Routing Protocol-Independent Features"), each route is advertised individually in an external LSA. However, you can configure the Cisco IOS software to advertise a single route for all the redistributed routes that are covered by a specified network address and mask. Doing so helps decrease the size of the OSPF link-state database.
To have the software advertise one summary route for all redistributed routes covered by a network address and mask, use the following command in router configuration mode:
Creating Virtual Links
In OSPF, all areas must be connected to a backbone area. If there is a break in backbone continuity, or the backbone is purposefully partitioned, you can establish a virtual link. The two endpoints of a virtual link are ABRs. The virtual link must be configured in both routers. The configuration information in each router consists of the other virtual endpoint (the other ABR) and the nonbackbone area that the two routers have in common (called the transit area). Note that virtual links cannot be configured through stub areas.
To establish a virtual link, use the following command in router configuration mode:
To display information about virtual links, use the show ip ospf virtual-links EXEC command. To display the router ID of an OSPF router, use the show ip ospf EXEC command.
Generating a Default Route
You can force an ASBR to generate a default route into an OSPF routing domain. Whenever you specifically configure redistribution of routes into an OSPF routing domain, the router automatically becomes an ASBR. However, an ASBR does not, by default, generate a default route into the OSPF routing domain.
To force the ASBR to generate a default route, use the following command in router configuration mode:
For a discussion of redistribution of routes, see the "Configuring IP Routing Protocol-Independent Features" chapter.
Configuring Lookup of DNS Names
You can configure OSPF to look up Domain Naming System (DNS) names for use in all OSPF show EXEC command displays. This feature makes it easier to identify a router, because the router is displayed by name rather than by its router ID or neighbor ID.
To configure DNS name lookup, use the following command in global configuration mode:
Forcing the Router ID Choice with a Loopback Interface
OSPF uses the largest IP address configured on the interfaces as its router ID. If the interface associated with this IP address is ever brought down, or if the address is removed, the OSPF process must recalculate a new router ID and resend all its routing information out its interfaces.
If a loopback interface is configured with an IP address, the Cisco IOS software will use this IP address as its router ID, even if other interfaces have larger IP addresses. Because loopback interfaces never go down, greater stability in the routing table is achieved.
OSPF automatically prefers a loopback interface over any other kind, and it chooses the highest IP address among all loopback interfaces. If no loopback interfaces are present, the highest IP address in the router is chosen. You cannot tell OSPF to use any particular interface.
To configure an IP address on a loopback interface, use the following commands beginning in global configuration mode:
Controlling Default Metrics
In Cisco IOS Release 10.3 and later releases, by default OSPF calculates the OSPF metric for an interface according to the bandwidth of the interface. For example, a 64-kbps link gets a metric of 1562, while a T1 link gets a metric of 64.
The OSPF metric is calculated as the ref-bw value divided by the bandwidth value, with the ref-bw value equal to 108 by default, and the bandwidth value determined by the bandwidth interface configuration command. The calculation gives FDDI a metric of 1. If you have multiple links with high bandwidth, you might want to specify a larger number to differentiate the cost on those links. To do so, use the following command in router configuration mode:
Router(config-router)# auto-cost reference-bandwidth ref-bw
Differentiates high bandwidth links.
Changing the OSPF Administrative Distances
An administrative distance is a rating of the trustworthiness of a routing information source, such as an individual router or a group of routers. Numerically, an administrative distance is an integer from 0 to 255. In general, the higher the value, the lower the trust rating. An administrative distance of 255 means the routing information source cannot be trusted at all and should be ignored.
OSPF uses three different administrative distances: intra-area, interarea, and external. Routes within an area are intra-area; routes to another area are interarea; and routes from another routing domain learned via redistribution are external. The default distance for each Type of route is 110.
To change any of the OSPF distance values, use the following command in router configuration mode:
Router(config-router)# distance ospf {[intra-area dist1] [inter-area dist2] [external dist3]}
Changes the OSPF distance values.
For an example of changing administrative distance, see the section "Changing OSPF Administrative Distance Example" at the end of this chapter.
Configuring OSPF on Simplex Ethernet Interfaces
Because simplex interfaces between two devices on an Ethernet represent only one network segment, for OSPF you must configure the sending interface to be a passive interface. This configuration prevents OSPF from sending hello packets for the sending interface. Both devices are able to see each other via the hello packet generated for the receiving interface.
To configure OSPF on simplex Ethernet interfaces, use the following command in router configuration mode:
Router(config-router)# passive-interface interface-type interface-number
Suppresses the sending of hello packets through the specified interface.
Configuring Route Calculation Timers
You can configure the delay time between when OSPF receives a topology change and when it starts a shortest path first (SPF) calculation. You can also configure the hold time between two consecutive SPF calculations. To do so, use the following command in router configuration mode:
Router(config-router)# timers spf spf-delay spf-holdtime
Configures route calculation timers.
Configuring OSPF over On-Demand Circuits
The OSPF on-demand circuit is an enhancement to the OSPF protocol that allows efficient operation over on-demand circuits like ISDN, X.25 switched virtual circuits (SVCs), and dialup lines. This feature supports RFC 1793, Extending OSPF to Support Demand Circuits.
Prior to this feature, OSPF periodic hello and LSA updates would be exchanged between routers that connected the on-demand link, even when no changes occurred in the hello or LSA information.
With this feature, periodic hellos are suppressed and the periodic refreshes of LSAs are not flooded over the demand circuit. These packets bring up the link only when they are exchanged for the first time, or when a change occurs in the information they contain. This operation allows the underlying data link layer to be closed when the network topology is stable.
This feature is useful when you want to connect telecommuters or branch offices to an OSPF backbone at a central site. In this case, OSPF for on-demand circuits allows the benefits of OSPF over the entire domain, without excess connection costs. Periodic refreshes of hello updates, LSA updates, and other protocol overhead are prevented from enabling the on-demand circuit when there is no "real" data to send.
Overhead protocols such as hellos and LSAs are transferred over the on-demand circuit only upon initial setup and when they reflect a change in the topology. This means that critical changes to the topology that require new SPF calculations are sent in order to maintain network topology integrity. Periodic refreshes that do not include changes, however, are not sent across the link.
To configure OSPF for on-demand circuits, use the following commands beginning in global configuration mode:
If the router is part of a point-to-point topology, then only one end of the demand circuit must be configured with this command. However, all routers must have this feature loaded.
If the router is part of a point-to-multipoint topology, only the multipoint end must be configured with this command.
For an example of OSPF over an on-demand circuit, see the section "OSPF over On-Demand Routing Example" at the end of this chapter.
Implementation Considerations
Evaluate the following considerations before implementing this feature:
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http://www.cisco.com/warp/public/104/dcprob.html#reason5Logging Neighbors Going Up or Down
By default, the system sends a syslog message when an OSPF neighbor goes up or down. If you turned off this feature and want to restore it, use the following command in router configuration mode:
Router(config-router)# log-adjacency-changes [detail]
Sends syslog message when an OSPF neighbor goes up or down.
Configure this command if you want to know about OSPF neighbors going up or down without turning on the debug ip ospf adjacency EXEC command. The log-adjacency-changes router configuration command provides a higher level view of the peer relationship with less output. Configure log-adjacency-changes detail if you want to see messages for each state change.
Changing the LSA Group Pacing
The OSPF LSA group pacing feature allows the router to group OSPF LSAs and pace the refreshing, checksumming, and aging functions. The group pacing results in more efficient use of the router.
The router groups OSPF LSAs and paces the refreshing, checksumming, and aging functions so that sudden increases in CPU usage and network resources are avoided. This feature is most beneficial to large OSPF networks.
OSPF LSA group pacing is enabled by default. For typical customers, the default group pacing interval for refreshing, checksumming, and aging is appropriate and you need not configure this feature.
Original LSA Behavior
Each OSPF LSA has an age, which indicates whether the LSA is still valid. Once the LSA reaches the maximum age (1 hour), it is discarded. During the aging process, the originating router sends a refresh packet every 30 minutes to refresh the LSA. Refresh packets are sent to keep the LSA from expiring, whether there has been a change in the network topology or not. Checksumming is performed on all LSAs every 10 minutes. The router keeps track of LSAs it generates and LSAs it receives from other routers. The router refreshes LSAs it generated; it ages the LSAs it received from other routers.
Prior to the LSA group pacing feature, the Cisco IOS software would perform refreshing on a single timer, and checksumming and aging on another timer. In the case of refreshing, for example, the software would scan the whole database every 30 minutes, refreshing every LSA the router generated, no matter how old it was. Figure 2 illustrates all the LSAs being refreshed at once. This process wasted CPU resources because only a small portion of the database needed to be refreshed. A large OSPF database (several thousand LSAs) could have thousands of LSAs with different ages. Refreshing on a single timer resulted in the age of all LSAs becoming synchronized, which resulted in much CPU processing at once. Furthermore, a large number of LSAs could cause a sudden increase of network traffic, consuming a large amount of network resources in a short period of time.
Figure 2 OSPF LSAs on a Single Timer Without Group Pacing
LSA Group Pacing With Multiple Timers
This problem is solved by configuring each LSA to have its own timer. To again use the example of refreshing, each LSA gets refreshed when it is 30 minutes old, independent of other LSAs. So the CPU is used only when necessary. However, LSAs being refreshed at frequent, random intervals would require many packets for the few refreshed LSAs the router must send out, which would be inefficient use of bandwidth.
Therefore, the router delays the LSA refresh function for an interval of time instead of performing it when the individual timers are reached. The accumulated LSAs constitute a group, which is then refreshed and sent out in one packet or more. Thus, the refresh packets are paced, as are the checksumming and aging. The pacing interval is configurable; it defaults to 4 minutes, which is randomized to further avoid synchronization.
Figure 3 illustrates the case of refresh packets. The first timeline illustrates individual LSA timers; the second timeline illustrates individual LSA timers with group pacing.
Figure 3 OSPF LSAs on Individual Timers with Group Pacing
The group pacing interval is inversely proportional to the number of LSAs the router is refreshing, checksumming, and aging. For example, if you have approximately 10,000 LSAs, decreasing the pacing interval would benefit you. If you have a very small database (40 to 100 LSAs), increasing the pacing interval to 10 to 20 minutes might benefit you slightly.
The default value of pacing between LSA groups is 240 seconds (4 minutes). The range is from 10 seconds to 1800 seconds (30 minutes). To change the LSA group pacing interval, use the following command in router configuration mode:
Router(config-router)# timers pacing lsa-group seconds
Changes the group pacing of LSAs.
For an example, see the section "LSA Group Pacing Example" at the end of this chapter.
Blocking OSPF LSA Flooding
By default, OSPF floods new LSAs over all interfaces in the same area, except the interface on which the LSA arrives. Some redundancy is desirable, because it ensures robust flooding. However, too much redundancy can waste bandwidth and might destabilize the network due to excessive link and CPU usage in certain topologies. An example would be a fully meshed topology.
You can block OSPF flooding of LSAs two ways, depending on the type of networks:
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On broadcast, nonbroadcast, and point-to-point networks, to prevent flooding of OSPF LSAs, use the following command in interface configuration mode:
Router(config-if)# ip ospf database-filter all out
Blocks the flooding of OSPF LSA packets to the interface.
On point-to-multipoint networks, to prevent flooding of OSPF LSAs, use the following command in router configuration mode:
Router(config-router)# neighbor ip-address database-filter all out
Blocks the flooding of OSPF LSA packets to the specified neighbor.
For an example of blocking LSA flooding, see the section "Block LSA Flooding Example" at the end of this chapter.
Reducing LSA Flooding
The explosive growth of the Internet has placed the focus on the scalability of IGPs such as OSPF. By design, OSPF requires LSAs to be refreshed as they expire after 3600 seconds. Some implementations have tried to improve the flooding by reducing the frequency to refresh from 30 minutes to about 50 minutes. This solution reduces the amount of refresh traffic but requires at least one refresh before the LSA expires. The OSPF flooding reduction solution works by reducing unnecessary refreshing and flooding of already known and unchanged information. To achieve this reduction, the LSAs are now flooded with the higher bit set. The LSAs are now set as "do not age."
To reduce unnecessary refreshing and flooding of LSAs on your network, use the following command in interface configuration mode:
Router(config-if)# ip ospf flood-reduction
Suppresses the unnecessary flooding of LSAs in stable topologies.
Ignoring MOSPF LSA Packets
Cisco routers do not support LSA Type 6 Multicast OSPF (MOSPF), and they generate syslog messages if they receive such packets. If the router is receiving many MOSPF packets, you might want to configure the router to ignore the packets and thus prevent a large number of syslog messages. To do so, use the following command in router configuration mode:
Router(config-router)# ignore lsa mospf
Prevents the router from generating syslog messages when it receives MOSPF LSA packets.
For an example of suppressing MOSPF LSA packets, see the section "Ignore MOSPF LSA Packets Example" at the end of this chapter.
Displaying OSPF Update Packet Pacing
The former OSPF implementation for sending update packets needed to be more efficient. Some update packets were getting lost in cases where the link was slow, a neighbor could not receive the updates quickly enough, or the router was out of buffer space. For example, packets might be dropped if either of the following topologies existed:
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OSPF update packets are now automatically paced so they are not sent less than 33 milliseconds apart. Pacing is also added between resends to increase efficiency and minimize lost retransmissions. Also, you can display the LSAs waiting to be sent out an interface. The benefit of the pacing is that OSPF update and retransmission packets are sent more efficiently.
There are no configuration tasks for this feature; it occurs automatically.
To observe OSPF packet pacing by displaying a list of LSAs waiting to be flooded over a specified interface, use the following command in EXEC mode:
Router# show ip ospf flood-list interface-type interface-number
Displays a list of LSAs waiting to be flooded over an interface.
Monitoring and Maintaining OSPF
You can display specific statistics such as the contents of IP routing tables, caches, and databases. Information provided can be used to determine resource utilization and solve network problems. You can also display information about node reachability and discover the routing path that your device packets are taking through the network.
To display various routing statistics, use the following commands in EXEC mode, as needed:
To restart an OSPF process, use the following command in EXEC mode:
Configuration Limits
On systems with a large number of interfaces, it may be possible to configure OSPF such that the number of links advertised in the router link-state advertisement (LSA) causes the link state update packet to exceed the size of a "huge" IOS buffer. To resolve this problem, reduce the number of OSPF links or increase the huge buffer size by entering the following command: buffers huge size size.
A link state update packet containing a router LSA typically has a fixed overhead of 196 bytes, and an additional 12 bytes are required for each link description. With a huge buffer size of 18024 bytes there can be a maximum of 1485 link descriptions.
Since the maximum size of an IP packet is 65535 bytes, there is still an upper bound on the number of links possible on a router.
OSPF Configuration Examples
The following sections provide OSPF configuration examples:
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OSPF Point-to-Multipoint Example
In Figure 4, the router named Mollie uses data-link connection identifier (DLCI) 201 to communicate with the router named Neon, DLCI 202 to the router named Jelly, and DLCI 203 to the router named Platty. Neon uses DLCI 101 to communicate with Mollie and DLCI 102 to communicate with Platty. Platty communicates with Neon (DLCI 401) and Mollie (DLCI 402). Jelly communicates with Mollie (DLCI 301). Configuration examples follow the figure.
Figure 4 OSPF Point-to-Multipoint Example
Mollie Configuration
hostname mollie!interface serial 1ip address 10.0.0.2 255.0.0.0ip ospf network point-to-multipointencapsulation frame-relayframe-relay map ip 10.0.0.1 201 broadcastframe-relay map ip 10.0.0.3 202 broadcastframe-relay map ip 10.0.0.4 203 broadcast!router ospf 1network 10.0.0.0 0.0.0.255 area 0Neon Configuration
hostname neon!interface serial 0ip address 10.0.0.1 255.0.0.0ip ospf network point-to-multipointencapsulation frame-relayframe-relay map ip 10.0.0.2 101 broadcastframe-relay map ip 10.0.0.4 102 broadcast!router ospf 1network 10.0.0.0 0.0.0.255 area 0Platty Configuration
hostname platty!interface serial 3ip address 10.0.0.4 255.0.0.0ip ospf network point-to-multipointencapsulation frame-relayclock rate 1000000frame-relay map ip 10.0.0.1 401 broadcastframe-relay map ip 10.0.0.2 402 broadcast!router ospf 1network 10.0.0.0 0.0.0.255 area 0Jelly Configuration
hostname jelly!interface serial 2ip address 10.0.0.3 255.0.0.0ip ospf network point-to-multipointencapsulation frame-relayclock rate 2000000frame-relay map ip 10.0.0.2 301 broadcast!router ospf 1network 10.0.0.0 0.0.0.255 area 0OSPF Point-to-Multipoint, Broadcast Example
The following example illustrates a point-to-multipoint network with broadcast:
interface Serial0ip address 10.0.1.1 255.255.255.0encapsulation frame-relayip ospf cost 100ip ospf network point-to-multipointframe-relay map ip 10.0.1.3 202 broadcastframe-relay map ip 10.0.1.4 203 broadcastframe-relay map ip 10.0.1.5 204 broadcastframe-relay local-dlci 200!router ospf 1network 10.0.1.0 0.0.0.255 area 0neighbor 10.0.1.5 cost 5neighbor 10.0.1.4 cost 10The following example shows the configuration of the neighbor at 10.0.1.3:
interface serial 0ip address 10.0.1.3 255.255.255.0ip ospf network point-to-multipointencapsulation frame-relayframe-relay local-dlci 301frame-relay map ip 10.0.1.1 300 broadcastno shut!router ospf 1network 10.0.1.0 0.0.0.255 area 0The output shown for neighbors in the first configuration is as follows:
Router# show ip ospf neighborNeighbor ID Pri State Dead Time Address Interface172.16.1.1 1 FULL/ - 00:01:50 10.0.1.5 Serial0172.16.1.4 1 FULL/ - 00:01:47 10.0.1.4 Serial0172.16.1.8 1 FULL/ - 00:01:45 10.0.1.3 Serial0The route information in the first configuration is as follows:
Router# show ip routeCodes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGPD - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter areaN1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGPi - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate defaultU - per-user static route, o - ODRGateway of last resort is not setC 1.0.0.0/8 is directly connected, Loopback010.0.0.0/8 is variably subnetted, 4 subnets, 2 masksO 10.0.1.3/32 [110/100] via 10.0.1.3, 00:39:08, Serial0C 10.0.1.0/24 is directly connected, Serial0O 10.0.1.5/32 [110/5] via 10.0.1.5, 00:39:08, Serial0O 10.0.1.4/32 [110/10] via 10.0.1.4, 00:39:08, Serial0OSPF Point-to-Multipoint, Nonbroadcast Example
The following example illustrates a point-to-multipoint network with nonbroadcast:
interface Serial0ip address 10.0.1.1 255.255.255.0ip ospf network point-to-multipoint non-broadcastencapsulation frame-relayno keepaliveframe-relay local-dlci 200frame-relay map ip 10.0.1.3 202frame-relay map ip 10.0.1.4 203frame-relay map ip 10.0.1.5 204no shut!router ospf 1network 10.0.1.0 0.0.0.255 area 0neighbor 10.0.1.3 cost 5neighbor 10.0.1.4 cost 10neighbor 10.0.1.5 cost 15The following example is the configuration for the router on the other side:
interface Serial9/2ip address 10.0.1.3 255.255.255.0encapsulation frame-relayip ospf network point-to-multipoint non-broadcastno ip mroute-cacheno keepaliveno fair-queueframe-relay local-dlci 301frame-relay map ip 10.0.1.1 300no shut!router ospf 1network 10.0.1.0 0.0.0.255 area 0The output shown for neighbors in the first configuration is as follows:
Router# show ip ospf neighborNeighbor ID Pri State Dead Time Address Interface172.16.1.1 1 FULL/ - 00:01:52 10.0.1.5 Serial0172.16.1.4 1 FULL/ - 00:01:52 10.0.1.4 Serial0172.16.1.8 1 FULL/ - 00:01:52 10.0.1.3 Serial0Variable-Length Subnet Masks Example
OSPF, static routes, and IS-IS support variable-length subnet masks (VLSMs). With VLSMs, you can use different masks for the same network number on different interfaces, which allows you to conserve IP addresses and more efficiently use available address space.
In the following example, a 30-bit subnet mask is used, leaving two bits of address space reserved for serial line host addresses. There is sufficient host address space for two host endpoints on a point-to-point serial link.
interface ethernet 0ip address 172.16.10.1 255.255.255.0! 8 bits of host address space reserved for ethernetsinterface serial 0ip address 172.16.20.1 255.255.255.252! 2 bits of address space reserved for serial lines! Router is configured for OSPF and assigned AS 107router ospf 107! Specifies network directly connected to the routernetwork 172.16.0.0 0.0.255.255 area 0.0.0.0OSPF NSSA Example
In the following example, an OSPF stub network is configured to include OSPF Area 0 and OSPF Area 1, using five routers. OSPF Area 1 is defined as a not-so-stubby area (NSSA), with Router 3 configured to be the NSSA autonomous system boundary router (ASBR) and Router 2 configured to be the NSSA area border router (ABR). Following are the configuration files for the five routers.
Router 1
hostname Router1!interface Loopback1ip address 10.1.0.1 255.255.255.255!interface Ethernet0/0ip address 192.168.0.1 255.255.255.0ip ospf 1 area 0no cdp enable!interface Serial10/0description Router2 interface s11/0ip address 192.168.10.1 255.255.255.0ip ospf 1 area 1serial restart-delay 0no cdp enable!router ospf 1area 1 nssa!endRouter 2
hostname Router2!!interface Loopback1ip address 10.1.0.2 255.255.255.255!interface Serial10/0description Router1 interface s11/0no ip addressshutdownserial restart-delay 0no cdp enable!interface Serial11/0description Router1 interface s10/0ip address 192.168.10.2 255.255.255.0ip ospf 1 area 1serial restart-delay 0no cdp enable!interface Serial14/0description Router3 interface s13/0ip address 192.168.14.2 255.255.255.0ip ospf 1 area 1serial restart-delay 0no cdp enable!router ospf 1area 1 nssa!endRouter 3
hostname Router3!interface Loopback1ip address 10.1.0.3 255.255.255.255!interface Ethernet3/0ip address 192.168.3.3 255.255.255.0no cdp enable!interface Serial13/0description Router2 interface s14/0ip address 192.168.14.3 255.255.255.0ip ospf 1 area 1serial restart-delay 0no cdp enable!router ospf 1log-adjacency-changesarea 1 nssaredistribute rip subnets!router ripversion 2redistribute ospf 1 metric 15network 192.168.3.0endRouter 4
hostname Router4!interface Loopback1ip address 10.1.0.4 255.255.255.255!interface Ethernet3/0ip address 192.168.3.4 255.255.255.0no cdp enable!interface Ethernet4/1ip address 192.168.41.4 255.255.255.0!router ripversion 2network 192.168.3.0network 192.168.41.0!endRouter 5
hostname Router5!interface Loopback1ip address 10.1.0.5 255.255.255.255!interface Ethernet0/0ip address 192.168.0.10 255.255.255.0ip ospf 1 area 0no cdp enable!interface Ethernet1/1ip address 192.168.11.10 255.255.255.0ip ospf 1 area 0!router ospf 1!endFigure 5 shows the OSPF stub network with NSSA Area 1. The redistributed routes that Router 4 is propagating from the two RIP networks will be translated into Type 7 LSAs by NSSA ASBR Router 3. Router 2, which is configured to be the NSSA ABR, will translate the Type 7 LSAs back to Type 5 so that they can be flooded through the rest of the OSPF stub network within OSPF Area 0.
Figure 5 OSPF NSSA Network with NSSA ABR and ASBR Routers
When the show ip ospf command is entered on Router 2, the output confirms that OSFP Area 1 is an NSSA area:
Router2# show ip ospfRouting Process "ospf 1" with ID 10.1.0.2Start time: 00:00:01.392, Time elapsed: 12:03:09.480Supports only single TOS(TOS0) routesSupports opaque LSASupports Link-local Signaling (LLS)Supports area transit capabilityRouter is not originating router-LSAs with maximum metricInitial SPF schedule delay 5000 msecsMinimum hold time between two consecutive SPFs 10000 msecsMaximum wait time between two consecutive SPFs 10000 msecsIncremental-SPF disabledMinimum LSA interval 5 secsMinimum LSA arrival 1000 msecsLSA group pacing timer 240 secsInterface flood pacing timer 33 msecsRetransmission pacing timer 66 msecsNumber of external LSA 0. Checksum Sum 0x000000Number of opaque AS LSA 0. Checksum Sum 0x000000Number of DCbitless external and opaque AS LSA 0Number of DoNotAge external and opaque AS LSA 0Number of areas in this router is 1. 0 normal 0 stub 1 nssaNumber of areas transit capable is 0External flood list length 0Area 1Number of interfaces in this area is 2! It is a NSSA areaArea has no authenticationSPF algorithm last executed 11:37:58.836 agoSPF algorithm executed 3 timesArea ranges areNumber of LSA 7. Checksum Sum 0x045598Number of opaque link LSA 0. Checksum Sum 0x000000Number of DCbitless LSA 0Number of indication LSA 0Number of DoNotAge LSA 0Flood list length 0Router2# show ip ospf dataOSPF Router with ID (10.1.0.2) (Process ID 1)Router Link States (Area 1)Link ID ADV Router Age Seq# Checksum Link count10.1.0.1 10.1.0.1 1990 0x80000016 0x00CBCB 210.1.0.2 10.1.0.2 1753 0x80000016 0x009371 410.1.0.3 10.1.0.3 1903 0x80000016 0x004149 2Summary Net Link States (Area 1)Link ID ADV Router Age Seq# Checksum192.168.0.0 10.1.0.1 1990 0x80000017 0x00A605192.168.11.0 10.1.0.1 1990 0x80000015 0x009503Type-7 AS External Link States (Area 1)Link ID ADV Router Age Seq# Checksum Tag192.168.3.0 10.1.0.3 1903 0x80000015 0x00484F 0192.168.41.0 10.1.0.3 1903 0x80000015 0x00A4CC 0Entering the show ip ospf database data command displays additional information about redistribution between Type 5 and Type 7 LSAs for routes that have been injected into the NSSA area and then flooded through the OSPF network.
Router2# show ip ospf database dataOSPF Router with ID (10.1.0.2) (Process ID 1)Area 1 database summaryLSA Type Count Delete MaxageRouter 3 0 0Network 0 0 0Summary Net 2 0 0Summary ASBR 0 0 0Type-7 Ext 2 0 0Prefixes redistributed in Type-7 0Opaque Link 0 0 0Opaque Area 0 0 0Subtotal 7 0 0Process 1 database summaryLSA Type Count Delete MaxageRouter 3 0 0Network 0 0 0Summary Net 2 0 0Summary ASBR 0 0 0Type-7 Ext 2 0 0Opaque Link 0 0 0Opaque Area 0 0 0Type-5 Ext 0 0 0Prefixes redistributed in Type-5 0Opaque AS 0 0 0Total 7 0 0Entering the show ip ospf database nssa command also displays detailed information for Type 7 to Type 5 translations:
Router2# show ip ospf database nssaOSPF Router with ID (10.1.0.2) (Process ID 1)Type-7 AS External Link States (Area 1)Routing Bit Set on this LSALS age: 1903Options: (No TOS-capability, Type 7/5 translation, DC)LS Type: AS External LinkLink State ID: 192.168.3.0 (External Network Number )Advertising Router: 10.1.0.3LS Seq Number: 80000015Checksum: 0x484FLength: 36Network Mask: /24Metric Type: 2 (Larger than any link state path)TOS: 0Metric: 20Forward Address: 192.168.14.3External Route Tag: 0Routing Bit Set on this LSALS age: 1903! Options: (No TOS-capability, Type 7/5 translation, DC)LS Type: AS External LinkLink State ID: 192.168.41.0 (External Network Number )Advertising Router: 10.1.0.3LS Seq Number: 80000015Checksum: 0xA4CCLength: 36Network Mask: /24Metric Type: 2 (Larger than any link state path)TOS: 0Metric: 20Forward Address: 192.168.14.3External Route Tag: 0Router 3
Entering the show ip ospf command on Router 3 displays the information to confirm that Router 3 is acting as an autonomous system boundary router (ASBR) and that OSPF Area 1 has been configured to be an NSSA area:
Router3# show ip ospfRouting Process "ospf 1" with ID 10.1.0.3Start time: 00:00:01.392, Time elapsed: 12:02:34.572Supports only single TOS(TOS0) routesSupports opaque LSASupports Link-local Signaling (LLS)Supports area transit capability!It is an autonomous system boundary routerRedistributing External Routes from,rip, includes subnets in redistributionRouter is not originating router-LSAs with maximum metricInitial SPF schedule delay 5000 msecsMinimum hold time between two consecutive SPFs 10000 msecsMaximum wait time between two consecutive SPFs 10000 msecsIncremental-SPF disabledMinimum LSA interval 5 secsMinimum LSA arrival 1000 msecsLSA group pacing timer 240 secsInterface flood pacing timer 33 msecsRetransmission pacing timer 66 msecsNumber of external LSA 0. Checksum Sum 0x000000Number of opaque AS LSA 0. Checksum Sum 0x000000Number of DCbitless external and opaque AS LSA 0Number of DoNotAge external and opaque AS LSA 0Number of areas in this router is 1. 0 normal 0 stub 1 nssaNumber of areas transit capable is 0External flood list length 0Area 1Number of interfaces in this area is 1! It is a NSSA areaArea has no authenticationSPF algorithm last executed 11:38:13.368 agoSPF algorithm executed 3 timesArea ranges areNumber of LSA 7. Checksum Sum 0x050CF7Number of opaque link LSA 0. Checksum Sum 0x000000Number of DCbitless LSA 0Number of indication LSA 0Number of DoNotAge LSA 0Flood list length 0OSPF Routing and Route Redistribution Examples
OSPF typically requires coordination among many internal routers, ABRs, and ASBRs. At a minimum, OSPF-based routers can be configured with all default parameter values, with no authentication, and with interfaces assigned to areas.
Three types of examples follow:
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Basic OSPF Configuration Examples
The following example illustrates a simple OSPF configuration that enables OSPF routing process 9000, attaches Ethernet interface 0 to area 0.0.0.0, and redistributes RIP into OSPF, and OSPF into RIP:
interface ethernet 0ip address 10.93.1.1 255.255.255.0ip ospf cost 1!interface ethernet 1ip address 10.94.1.1 255.255.255.0!router ospf 9000network 10.93.0.0 0.0.255.255 area 0.0.0.0redistribute rip metric 1 subnets!router ripnetwork 10.94.0.0redistribute ospf 9000default-metric 1Basic OSPF Configuration Example for Internal Router, ABR, and ASBRs
The following example illustrates the assignment of four area IDs to four IP address ranges. In the example, OSPF routing process 109 is initialized, and four OSPF areas are defined: 10.9.50.0, 2, 3, and 0. Areas 10.9.50.0, 2, and 3 mask specific address ranges, and area 0 enables OSPF for all other networks.
router ospf 109network 192.168.10.0 0.0.0.255 area 10.9.50.0network 192.168.20.0 0.0.255.255 area 2network 192.168.30.0 0.0.0.255 area 3network 192.168.40.0 255.255.255.255 area 0!! Interface Ethernet0 is in area 10.9.50.0:interface ethernet 0ip address 192.168.10.5 255.255.255.0!! Interface Ethernet1 is in area 2:interface ethernet 1ip address 192.168.20.5 255.255.255.0!! Interface Ethernet2 is in area 2:interface ethernet 2ip address 192.168.20.7 255.255.255.0!! Interface Ethernet3 is in area 3:interface ethernet 3ip address 192.169.30.5 255.255.255.0!! Interface Ethernet4 is in area 0:interface ethernet 4ip address 192.168.40.1 255.255.255.0!! Interface Ethernet5 is in area 0:interface ethernet 5ip address 192.168.40.12 255.255.0.0Each network area router configuration command is evaluated sequentially, so the order of these commands in the configuration is important. The Cisco IOS software sequentially evaluates the address/wildcard-mask pair for each interface. See the "OSPF Commands" chapter of the Cisco IOS IP Routing Protocols Command Reference for more information.
Consider the first network area command. Area ID 10.9.50.0 is configured for the interface on which subnet 192.168.10.0 is located. Assume that a match is determined for Ethernet interface 0. Ethernet interface 0 is attached to area 10.9.50.0 only.
The second network area command is evaluated next. For area 2, the same process is then applied to all interfaces (except Ethernet interface 0). Assume that a match is determined for interface Ethernet 1. OSPF is then enabled for that interface and Ethernet interface 1 is attached to area 2.
This process of attaching interfaces to OSPF areas continues for all network area commands. Note that the last network area command in this example is a special case. With this command, all available interfaces (not explicitly attached to another area) are attached to area 0.
Complex Internal Router, ABR, and ASBRs Example
The following example outlines a configuration for several routers within a single OSPF autonomous system. Figure 6 provides a general network map that illustrates this example configuration.
Figure 6 Sample OSPF Autonomous System Network Map
In this configuration, five routers are configured with OSPF:
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The OSPF domain in BGP autonomous system 109 is connected to the outside world via the BGP link to the external peer at IP address 11.0.0.6. Example configurations follow.
Following is the sample configuration for the general network map shown in Figure 6.
Router A Configuration—Internal Router
interface ethernet 1ip address 192.168.1.1 255.255.255.0router ospf 1network 192.168.0.0 0.0.255.255 area 1Router B Configuration—Internal Router
interface ethernet 2ip address 192.168.1.2 255.255.255.0router ospf 202network 192.168.0.0 0.0.255.255 area 1Router C Configuration—ABR
interface ethernet 3ip address 192.168.1.3 255.255.255.0interface serial 0ip address 192.168.2.3 255.255.255.0router ospf 999network 192.168.1.0 0.0.0.255 area 1network 192.168.2.0 0.0.0.255 area 0Router D Configuration—Internal Router
interface ethernet 4ip address 10.0.0.4 255.0.0.0interface serial 1ip address 192.168.2.4 255.255.255.0router ospf 50network 192.168.2.0 0.0.0.255 area 0network 10.0.0.0 0.255.255.255 area 0Router E Configuration—ASBR
interface ethernet 5ip address 10.0.0.5 255.0.0.0interface serial 2ip address 172.16.1.5 255.255.255.0router ospf 65001network 10.0.0.0 0.255.255.255 area 0redistribute bgp 109 metric 1 metric-type 1router bgp 109network 192.168.0.0network 10.0.0.0neighbor 172.16.1.6 remote-as 110Complex OSPF Configuration for ABR Examples
The following example configuration accomplishes several tasks in setting up an ABR. These tasks can be split into two general categories:
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The specific tasks outlined in this configuration are detailed briefly in the following descriptions. Figure 7 illustrates the network address ranges and area assignments for the interfaces.
Figure 7 Interface and Area Specifications for OSPF Example Configuration
The basic configuration tasks in this example are as follows:
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Configuration tasks associated with redistribution are as follows:
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The following is an example OSPF configuration:
interface ethernet 0ip address 192.42.110.201 255.255.255.0ip ospf authentication-key abcdefghip ospf cost 10!interface ethernet 1ip address 172.19.251.202 255.255.255.0ip ospf authentication-key ijklmnopip ospf cost 20ip ospf retransmit-interval 10ip ospf transmit-delay 2ip ospf priority 4!interface ethernet 2ip address 172.19.254.2 255.255.255.0ip ospf authentication-key abcdefghip ospf cost 10!interface ethernet 3ip address 10.56.0.0 255.255.0.0ip ospf authentication-key ijklmnopip ospf cost 20ip ospf dead-interval 80In the following configuration OSPF is on network 172.16.0.0:
router ospf 201network 10.10.0.0 0.255.255.255 area 10.10.0.0network 192.42.110.0 0.0.0.255 area 192.42.110.0network 172.16.0.0 0.0.255.255 area 0area 0 authenticationarea 10.10.0.0 stubarea 10.10.0.0 authenticationarea 10.10.0.0 default-cost 20area 192.42.110.0 authenticationarea 10.10.0.0 range 10.10.0.0 255.0.0.0area 192.42.110.0 range 192.42.110.0 255.255.255.0area 0 range 172.16.251.0 255.255.255.0area 0 range 172.16.254.0 255.255.255.0redistribute igrp 200 metric-type 2 metric 1 tag 200 subnetsredistribute rip metric-type 2 metric 1 tag 200In the following configuration IGRP autonomous system 200 is on 131.119.0.0:
router igrp 200network 172.31.0.0!! RIP for 192.168.110!router ripnetwork 192.168.110.0redistribute igrp 200 metric 1redistribute ospf 201 metric 1Route Map Examples
The examples in this section illustrate the use of redistribution, with and without route maps. Examples from both the IP and Connectionless Network Service (CLNS) routing protocols are given.
The following example redistributes all OSPF routes into IGRP:
router igrp 109redistribute ospf 110The following example redistributes RIP routes with a hop count equal to 1 into OSPF. These routes will be redistributed into OSPF as external LSAs with a metric of 5, a metric type of Type 1, and a tag equal to 1.
router ospf 109redistribute rip route-map rip-to-ospf!route-map rip-to-ospf permitmatch metric 1set metric 5set metric-type type1set tag 1The following example redistributes OSPF learned routes with tag 7 as a RIP metric of 15:
router ripredistribute ospf 109 route-map 5!route-map 5 permitmatch tag 7set metric 15The following example redistributes OSPF intra-area and interarea routes with next hop routers on serial interface 0 into BGP with an INTER_AS metric of 5:
router bgp 109redistribute ospf 109 route-map 10!route-map 10 permitmatch route-type internalmatch interface serial 0set metric 5The following example redistributes two types of routes into the integrated IS-IS routing table (supporting both IP and CLNS). The first type is OSPF external IP routes with tag 5; these routes are inserted into Level 2 IS-IS LSPs with a metric of 5. The second type is ISO-IGRP derived CLNS prefix routes that match CLNS access list 2000; these routes will be redistributed into IS-IS as Level 2 LSPs with a metric of 30.
router isisredistribute ospf 109 route-map 2redistribute iso-igrp nsfnet route-map 3 !route-map 2 permitmatch route-type externalmatch tag 5set metric 5set level level-2!route-map 3 permitmatch address 2000set metric 30With the following configuration, OSPF external routes with tags 1, 2, 3, and 5 are redistributed into RIP with metrics of 1, 1, 5, and 5, respectively. The OSPF routes with a tag of 4 are not redistributed.
router ripredistribute ospf 109 route-map 1!route-map 1 permitmatch tag 1 2set metric 1!route-map 1 permitmatch tag 3set metric 5!route-map 1 denymatch tag 4!route map 1 permitmatch tag 5set metric 5In the following configuration, a RIP learned route for network 160.89.0.0 and an ISO-IGRP learned route with prefix 49.0001.0002 will be redistributed into an IS-IS Level 2 LSP with a metric of 5:
router isisredistribute rip route-map 1redistribute iso-igrp remote route-map 1!route-map 1 permitmatch ip address 1match clns address 2set metric 5set level level-2!access-list 1 permit 192.168.0.0 0.0.255.255clns filter-set 2 permit 49.0001.0002...The following configuration example illustrates how a route map is referenced by the default-information router configuration command. This type of reference is called conditional default origination. OSPF will originate the default route (network 0.0.0.0) with a Type 2 metric of 5 if 140.222.0.0 is in the routing table.
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route-map ospf-default permitmatch ip address 1set metric 5set metric-type type-2!access-list 1 permit 172.16.0.0 0.0.255.255!router ospf 109default-information originate route-map ospf-defaultChanging OSPF Administrative Distance Example
The following configuration changes the external distance to 200, making it less trustworthy. Figure 8 illustrates the example.
Figure 8 OSPF Administrative Distance
Router A Configuration
router ospf 1 redistribute ospf 2 subnet distance ospf external 200 ! router ospf 2redistribute ospf 1 subnet distance ospf external 200Router B Configuration
router ospf 1 redistribute ospf 2 subnet distance ospf external 200 ! router ospf 2redistribute ospf 1 subnet distance ospf external 200OSPF over On-Demand Routing Example
The following configuration allows OSPF over an on-demand circuit, as shown in Figure 9. Note that the on-demand circuit is defined on one side only BRI 0 on Router A). It is not required to be configured on both sides.
Figure 9 OSPF over On-Demand Circuit
Router A Configuration
username RouterB password 7 060C1A2F47isdn switch-type basic-5essip routing!interface TokenRing0ip address 192.168.50.5 255.255.255.0no shut!interface BRI0no cdp enabledescription connected PBX 1485ip address 192.168.45.30 255.255.255.0encapsulation pppip ospf demand-circuitdialer map ip 140.10.10.6 name RouterB broadcast 61484dialer-group 1ppp authentication chapno shut!router ospf 100network 192.168.45.0 0.0.0.255 area 0network 192.168.45.50 0.0.0.255 area 0!dialer-list 1 protocol ip permitRouter B Configuration
username RouterA password 7 04511E0804isdn switch-type basic-5essip routing!interface Ethernet0ip address 192.168.50.16 255.255.255.0no shut!interface BRI0no cdp enabledescription connected PBX 1484ip address 192.168.45.17 255.255.255.0encapsulation pppdialer map ip 192.168.45.19 name RouterA broadcast 61485dialer-group 1ppp authentication chapno shut!router ospf 100network 192.168.45.0 0.0.0.255 area 0network 192.168.45.50 0.0.0.255 area 0!dialer-list 1 protocol ip permitLSA Group Pacing Example
The following example changes the OSPF pacing between LSA groups to 60 seconds:
router ospftimers pacing lsa-group 60Block LSA Flooding Example
The following example prevents flooding of OSPF LSAs to broadcast, nonbroadcast, or point-to-point networks reachable through Ethernet interface 0:
interface ethernet 0ip ospf database-filter all outThe following example prevents flooding of OSPF LSAs to point-to-multipoint networks to the neighbor at IP address 1.2.3.4:
router ospf 109neighbor 10.10.10.45 database-filter all outIgnore MOSPF LSA Packets Example
The following example configures the router to suppress the sending of syslog messages when it receives MOSPF packets:
router ospf 109ignore lsa mospf
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