Configuring Internet Protocol (IP) routing

gated OSPF protocol statement

   ospf yes|no|on|off [ {
       [ defaults {
           preference preference ;
           cost cost ;
           tag [tag | as [as_tag]] ;
           type 1|2 ;
       } ] ;
       [exportlimit routes ;]
       [exportinterval time ;]
       [traceoptions traceoptions ;]
       [monitorauthkey authkey ;]
       [area area {
           authtype 0|1|none|simple ;
           stub [cost cost];
           networks {
               network [mask mask] ;
           } ;
           stubhosts {
               host cost cost ;
           } ;
           interface interface [cost cost] {
               [enable|disable] ;
               retransmitinterval time ;
               transitdelay time ;
               priority priority ;
               hellointerval time ;
               routerdeadinterval time ;
               authkey auth_key ;
           } ;
           interface interface nonbroadcast [cost cost] {
               pollinterval time ;
               routers {
                   gateway [eligible] ;
                   . . .
               } ;
               [enable|disable] ;
               retransmitinterval time ;
               transitdelay time ;
               priority priority ;
               hellointerval time ;
               routerdeadinterval time ;
               authkey auth_key ;
           } ;
       } ; ]


       [ backbone {
           authtype 0|1|none|simple ;
           networks {
               network [mask mask] ;
           } ;
           stubhosts {
               host cost cost ;
           } ;
           interface interface [cost cost] {
               [enable|disable] ;
               retransmitinterval time ;
               transitdelay time ;
               priority priority ;
               hellointerval time ;
               routerdeadinterval time ;
               authkey auth_key ;
           } ;
           . . .
           interface interface nonbroadcast [cost cost] {
               pollinterval time ;
               routers {
                   gateway [eligible] ;
                   . . .
               } ;
               [enable|disable] ;
               retransmitinterval time ;
               transitdelay time ;
               priority priority ;
               hellointerval time ;
               routerdeadinterval time ;
               authkey auth_key ;
           } ;
           . . .
           virtuallink neighborid host transitarea area {
               [enable|disable] ;
               retransmitinterval time ;
               transitdelay time ;
               priority priority ;
               hellointerval time ;
               routerdeadinterval time ;
               authkey auth_key ;
           } ;
           . . .
       } ; ]
   } ] ;

defaults

These parameters specify the defaults used when importing OSPF ASE routes into the gated routing table and exporting routes from the gated routing table into OSPF ASEs. The following defines each statement:

preference preference: The preference is used to determine how OSPF routes compete with routes from other protocols in the gated routing table. The default value is 150.
cost cost: The cost is used when exporting a non-OSPF route from the gated routing table into OSPF as an ASE. The default value is 1. This may be explicitly overridden in export policy.
tag [ as ] tag: OSPF ASE routes have a 32-bit tag field that is not used by the OSPF protocol but may be used by export policy to filter routes. When OSPF is interacting with an egp, the tag field may be used to propagate AS path information, in which case the as keyword is specified that the tag is limited to 12 bits of information. If not specified, the tag is set to zero.
type 1 | 2: Routes exported from the gated routing table into OSPF default to becoming type 1 ASEs. This default may be explicitly changed here and overridden in export policy.

ASE export rate

Because of the nature of OSPF, the rate at which ASEs are flooded must be limited. These two parameters can be used to adjust those rate limits.

exportinterval time: This specifies how often a batch of ASE link-state advertisements will be generated and flooded into OSPF. The default is once per second.
exportlimit routes: This parameter specifies how many ASEs will be generated and flooded in each batch. The default is 100.

traceoptions traceoptions

Specifies the tracing options for OSPF. (See ``gated trace statements'').

monitorauthkey authkey

OSPF state may be queried using the ospf_monitor utility (see ospf_monitor(ADMN). This utility sends nonstandard OSPF packets that generate a text response from OSPF. By default, these requests are not authenticated. If an authentication key is configured, the incoming requests must match the specified authentication key. No OSPF state may be changed by these packets, but the act of querying OSPF can utilize system resources.

backbone area area

Each OSPF router must be configured into at least one OSPF area. If more than one area is configured, at least one must be the backbone. The backbone may only be configured using the backbone keyword; it may not be specified as area 0. The backbone interface may be a ``virtuallink''.

authtype 0 | 1 | none | simple: OSPF specifies an authentication scheme per area. Each interface in the area must use this same authentication scheme, although it may use a different authentication key. The currently valid values are none (0) for no authentication, or simple (1) for simple password authentication.
stub [ cost cost]: A stub area is one in which there are no ASE routes. If a cost is specified, this is used to inject a default route into the area with the specified cost.
networks: The networks list describes the scope of an area. Intra-area LSAs that fall within the specified ranges are not advertised into other areas as inter-area routes. Instead, the specified ranges are advertised as summary network LSAs. Intra-area LSAs that do not fall into any range are also advertised as summary network LSAs. This option is very useful on well-designed networks in reducing the amount of routing information propagated between areas. The entries in this list are either networks or a subnetwork/mask pair. See ``gated route filtering'' for more detail about specifying ranges.
stubhosts: This list specifies directly attached hosts that should be advertised as reachable from this router and the costs they should be advertised with. Point-to-point interfaces on which it is not desirable to run OSPF should be specified here.
It is also useful to assign an additional address to the loopback interface (one not on the 127 network) and advertise it as a stubhosts. If this address is the same one used as the router-id, it enables routing to OSPF routers by router-id instead of by interface address. This is more reliable than routing to one of the router interface addresses that may not always be reachable.

interface interface_list [cost cost ]

This form of the interface clause is used to configure a broadcast (which requires IP multicast support) or a point-to-point interface. See ``gated interfaces statements'' for the description of the interface_list.

Each interface has a cost. The costs of all interfaces a packet must cross to reach a destination are summed to get the cost to that destination. The default cost is one, but another nonzero value may be specified.

Interface parameters common to all types of interface are:

retransmitinterval time: The number of seconds between link-state advertisement retransmissions for adjacencies belonging to this interface.
transitdelay time: The estimated number of seconds required to transmit a link-state update over this interface. Transitdelay takes into account transmission and propagation delays and must be greater than 0.
priority priority: A number between 0 and 255 specifying the priority for becoming the designated router on this interface. When two routers attached to a network both attempt to become the designated router, the one with the higher priority wins. A router whose router priority is set to 0 is ineligible to become designated router.
hellointerval time: The length of time, in seconds, between Hello packets that the router sends on the interface.
routerdeadinterval time: The number of seconds of not hearing a router's Hello packets before the router's neighbors will declare it down.
authkey auth_key: Used by OSPF authentication to generate and verify the authentication field in the OSPF header. The authentication key can be configured on a per-interface basis. It is specified by one to eight decimal digits separated by periods, a one to eight byte hexadecimal string preceded by 0x, or a one to eight character string in double quotes.

interface interface_list nonbroadcast [ cost cost ]

This form of the interface clause is used to specify a nonbroadcast interface on a nonbroadcast multiaccess (NBMA) media. Since an OSPF broadcast media must support IP multicasting, a broadcast capable media, such as Ethernet, that does not support IP multicasting must be configured as a nonbroadcast interface.

A nonbroadcast interface supports any of the standard interface clauses listed above, plus the following two that are specific to nonbroadcast interfaces:

pollinterval time: Before adjacency is established with a neighbor, OSPF packets are sent periodically at the specified time.
routers: By definition, it is not possible to send broadcast packets to discover OSPF neighbors on a nonbroadcast, so all neighbors must be configured. The list includes one or more neighbors and an indication of their eligibility to become a designated router.

virtuallink neighborid host transitarea area

Virtual links are used to establish or increase connectivity of the backbone area. host is the router-id of the other end of the virtual link. The transit area specified must also be configured on this system. All standard interface parameters defined by the interface clause above may be specified on a virtual link.