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7.3 OSPF router

To start OSPF process you have to specify the OSPF router. As of this writing, ospfd does not support multiple OSPF processes.

Command: router ospf
Command: no router ospf

Enable or disable the OSPF process. ospfd does not yet support multiple OSPF processes. So you can not specify an OSPF process number.

OSPF Command: ospf router-id a.b.c.d
OSPF Command: no ospf router-id

This sets the router-ID of the OSPF process. The router-ID may be an IP address of the router, but need not be - it can be any arbitrary 32bit number. However it MUST be unique within the entire OSPF domain to the OSPF speaker - bad things will happen if multiple OSPF speakers are configured with the same router-ID! If one is not specified then ospfd will obtain a router-ID automatically from zebra.

OSPF Command: ospf abr-type type
OSPF Command: no ospf abr-type type

type can be cisco|ibm|shortcut|standard. The "Cisco" and "IBM" types are equivalent.

The OSPF standard for ABR behaviour does not allow an ABR to consider routes through non-backbone areas when its links to the backbone are down, even when there are other ABRs in attached non-backbone areas which still can reach the backbone - this restriction exists primarily to ensure routing-loops are avoided.

With the "Cisco" or "IBM" ABR type, the default in this release of Quagga, this restriction is lifted, allowing an ABR to consider summaries learnt from other ABRs through non-backbone areas, and hence route via non-backbone areas as a last resort when, and only when, backbone links are down.

Note that areas with fully-adjacent virtual-links are considered to be "transit capable" and can always be used to route backbone traffic, and hence are unaffected by this setting (see OSPF virtual-link).

More information regarding the behaviour controlled by this command can be found in RFC 3509, Alternative Implementations of OSPF Area Border Routers, and draft-ietf-ospf-shortcut-abr-02.txt.

Quote: "Though the definition of the ABR (Area Border Router) in the OSPF specification does not require a router with multiple attached areas to have a backbone connection, it is actually necessary to provide successful routing to the inter-area and external destinations. If this requirement is not met, all traffic destined for the areas not connected to such an ABR or out of the OSPF domain, is dropped. This document describes alternative ABR behaviors implemented in Cisco and IBM routers."

OSPF Command: ospf rfc1583compatibility
OSPF Command: no ospf rfc1583compatibility

RFC2328, the sucessor to RFC1583, suggests according to section G.2 (changes) in section 16.4 a change to the path preference algorithm that prevents possible routing loops that were possible in the old version of OSPFv2. More specifically it demands that inter-area paths and intra-area backbone path are now of equal preference but still both preferred to external paths.

This command should NOT be set normally.

OSPF Command: log-adjacency-changes [detail]
OSPF Command: no log-adjacency-changes [detail]

Configures ospfd to log changes in adjacency. With the optional detail argument, all changes in adjacency status are shown. Without detail, only changes to full or regressions are shown.

OSPF Command: passive-interface interface
OSPF Command: no passive-interface interface

Do not speak OSPF interface on the given interface, but do advertise the interface as a stub link in the router-LSA (Link State Advertisement) for this router. This allows one to advertise addresses on such connected interfaces without having to originate AS-External/Type-5 LSAs (which have global flooding scope) - as would occur if connected addresses were redistributed into OSPF (see Redistribute routes to OSPF). This is the only way to advertise non-OSPF links into stub areas.

OSPF Command: timers throttle spf delay initial-holdtime max-holdtime
OSPF Command: no timers throttle spf

This command sets the initial delay, the initial-holdtime and the maximum-holdtime between when SPF is calculated and the event which triggered the calculation. The times are specified in milliseconds and must be in the range of 0 to 600000 milliseconds.

The delay specifies the minimum amount of time to delay SPF calculation (hence it affects how long SPF calculation is delayed after an event which occurs outside of the holdtime of any previous SPF calculation, and also serves as a minimum holdtime).

Consecutive SPF calculations will always be seperated by at least ’hold-time’ milliseconds. The hold-time is adaptive and initially is set to the initial-holdtime configured with the above command. Events which occur within the holdtime of the previous SPF calculation will cause the holdtime to be increased by initial-holdtime, bounded by the maximum-holdtime configured with this command. If the adaptive hold-time elapses without any SPF-triggering event occuring then the current holdtime is reset to the initial-holdtime. The current holdtime can be viewed with show ip ospf, where it is expressed as a multiplier of the initial-holdtime.

router ospf
 timers throttle spf 200 400 10000

In this example, the delay is set to 200ms, the initial holdtime is set to 400ms and the maximum holdtime to 10s. Hence there will always be at least 200ms between an event which requires SPF calculation and the actual SPF calculation. Further consecutive SPF calculations will always be seperated by between 400ms to 10s, the hold-time increasing by 400ms each time an SPF-triggering event occurs within the hold-time of the previous SPF calculation.

This command supercedes the timers spf command in previous Quagga releases.

OSPF Command: max-metric router-lsa [on-startup|on-shutdown] <5-86400>
OSPF Command: max-metric router-lsa administrative
OSPF Command: no max-metric router-lsa [on-startup|on-shutdown|administrative]

This enables RFC3137, OSPF Stub Router Advertisement support, where the OSPF process describes its transit links in its router-LSA as having infinite distance so that other routers will avoid calculating transit paths through the router while still being able to reach networks through the router.

This support may be enabled administratively (and indefinitely) or conditionally. Conditional enabling of max-metric router-lsas can be for a period of seconds after startup and/or for a period of seconds prior to shutdown.

Enabling this for a period after startup allows OSPF to converge fully first without affecting any existing routes used by other routers, while still allowing any connected stub links and/or redistributed routes to be reachable. Enabling this for a period of time in advance of shutdown allows the router to gracefully excuse itself from the OSPF domain.

Enabling this feature administratively allows for administrative intervention for whatever reason, for an indefinite period of time. Note that if the configuration is written to file, this administrative form of the stub-router command will also be written to file. If ospfd is restarted later, the command will then take effect until manually deconfigured.

Configured state of this feature as well as current status, such as the number of second remaining till on-startup or on-shutdown ends, can be viewed with the show ip ospf command.

OSPF Command: auto-cost reference-bandwidth <1-4294967>
OSPF Command: no auto-cost reference-bandwidth

This sets the reference bandwidth for cost calculations, where this bandwidth is considered equivalent to an OSPF cost of 1, specified in Mbits/s. The default is 100Mbit/s (i.e. a link of bandwidth 100Mbit/s or higher will have a cost of 1. Cost of lower bandwidth links will be scaled with reference to this cost).

This configuration setting MUST be consistent across all routers within the OSPF domain.

OSPF Command: network a.b.c.d/m area a.b.c.d
OSPF Command: network a.b.c.d/m area <0-4294967295>
OSPF Command: no network a.b.c.d/m area a.b.c.d
OSPF Command: no network a.b.c.d/m area <0-4294967295>

This command specifies the OSPF enabled interface(s). If the interface has an address from range then the command below enables ospf on this interface so router can provide network information to the other ospf routers via this interface.

router ospf
 network area

Prefix length in interface must be equal or bigger (ie. smaller network) than prefix length in network statement. For example statement above doesn’t enable ospf on interface with address, but it does on interface with address

Note that the behavior when there is a peer address defined on an interface changed after release 0.99.7. Currently, if a peer prefix has been configured, then we test whether the prefix in the network command contains the destination prefix. Otherwise, we test whether the network command prefix contains the local address prefix of the interface.

In some cases it may be more convenient to enable OSPF on a per interface/subnet basis (see OSPF ip ospf area command).

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