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The OSPF: Limit Simultaneous Adjacency Formations feature allows you to limit to the number of adjacencies that are in “exchange” or “loading” state at the same time. A process limit (PL) determines the number of “forming” adjacencies and applies to all adjacencies for the entire process. The term “forming” refers to adjacencies that are in “exchange” or “loading” state. Adjacencies form in an OSPF area during the initial period after the area is created. The Initial Limit applies when no adjacencies have reached the “full” state in an OSPF area. If there are any “full” adjacencies in the area, the new adjacencies are governed by the Process Limit. At a given point of time, process limit and initial limit are effective in an OSPF area. When there are no adjacencies “forming” in an area, at least one adjacency is allowed to form regardless of the maximum limit specified for it. In other words, the maximum number of adjacencies can be exceeded before adjacencies form in one or more areas. The maximum limit can be exceeded by the number of areas minus one.

When a limit is reached, adjacencies in a state less than EXCHANGE are terminated. To terminate the adjacency, a hello packet is sent to the neighbor which does not have the neighbor’s device ID. This causes the neighbor to put the adjacency in the INIT state. This prevents a deadlock with the neighbor, which could otherwise happen if the neighbor is blocking an adjacency from forming on a different interface. By causing the neighbor to bring the adjacency to INIT, it allows the neighbor to form an adjacency on a different interface. Packets from unknown neighbors are ignored when the limit has been reached or exceeded.

If graceful restart or Cisco nonstop forwarding is configured, the hello packets must be accepted from every neighboring device The restarting device must include the neighbors’ device IDs in its hello packets to prevent the adjacency from being dropped by the neighbor. If graceful restart is in configured, the grace link-state advertisements (LSAs) must be sent in a normal mode and not in a throttling mode. When the device is performing graceful restart and if the limit is reached, new adjacencies are allowed to remain in 2-WAY or EXSTART. However, they are prevented from proceeding to EXCHANGE until the number of forming adjacencies is less than the limit.

Use the adjacency stagger command to configure the maximum limit and the initial limit for an area in the router or address-family configuration modes. The initial limit must not be greater than the process limit. The default value is 300 and the minimum is 1. If the none keyword is used, the maximum limit is only effective. The none keyword also disables the initial limit for areas. If an initial limit is reached in an area and no adjacencies are forming, no adjacencies will be allowed to form in the area until global number of adjacencies forming is less than the PL.

Use the ip ospf adjacency stagger disable or the ospfv3 adjacency stagger disable command to disable staggering on an interface. Adjacencies forming on a disabled interface are counted towards throttling limits. Disabling the throttling on an interface allows exceeding the maximum limit when the maximum limit is reached and a new adjacency forms on an interface where throttling is disabled.

Note

When using the no adjacency stagger command to disable the feature, the command is displayed in the running configuration. To return to the default values, use the default adjacency stagger command. After using this command, the adjacency stagger command does not appear in the running configuration.

1.    enable


2.    configure terminal


3.    router ospf process-id


4.    adjacency stagger {initial-limit | none} maximum-limit


5.    end

Device> enable

Device# configure terminal

Device(config)# router ospf 109

Device(config-router)# adjacency stagger 10 50

Device(config-router)# end

1.    enable


2.    configure terminal


3.    router ospfv3 [process-id]


4.    Do one of the following:

• address-family ipv4 unicast
• address-family ipv6 unicast

5.    adjacency stagger {initial-limit | none} {maximum-limit| disable}


6.    end

Device> enable

Device# configure terminal

Device(config)# router ospfv3 1

Device(config-router)# address-family ipv4 unicast 

Device(config-router)# address-family ipv6 unicast 

Device(config-router-af)# adjacency stagger 10 50

Device(config-router-af)# end

1.    enable


2.    configure terminal


3.    interface type number


4.    Do one of the following:

• ip ospf adjacency stagger disable
• ospfv3 adjacency stagger disable

5.    end

Device> enable

Device# configure terminal

Device(config)# interface serial 2/0

Device(config-if)# ip ospf adjacency stagger disable

Device(config-if)# ospfv3 adjacency stagger disable

Device(config-if)# end

1.    enable


2.    show ip ospf


3.    show ospfv3

Device> enable

Device# show ip ospf

 Routing Process "ospf 10" with ID 10.8.3.3
 Start time: 2w0d, Time elapsed: 00:16:43.033
 Supports only single TOS(TOS0) routes
 Supports opaque LSA
 Supports Link-local Signaling (LLS)
 Supports area transit capability
 Supports NSSA (compatible with RFC 3101)
 Supports Database Exchange Summary List Optimization (RFC 5243)
 Event-log enabled, Maximum number of events: 1000, Mode: cyclic
 Router is not originating router-LSAs with maximum metric
 Initial SPF schedule delay 5000 msecs
 Minimum hold time between two consecutive SPFs 10000 msecs
 Maximum wait time between two consecutive SPFs 10000 msecs
 Incremental-SPF disabled
 Minimum LSA interval 5 secs
 Minimum LSA arrival 1000 msecs
 LSA group pacing timer 240 secs
 Interface flood pacing timer 33 msecs
 Retransmission pacing timer 66 msecs
 EXCHANGE/LOADING adjacency limit: initial 300, process maximum 300
 Number of external LSA 0. Checksum Sum 0x000000
 Number of opaque AS LSA 0. Checksum Sum 0x000000
 Number of DCbitless external and opaque AS LSA 0
 Number of DoNotAge external and opaque AS LSA 0
 Number of areas in this router is 0. 0 normal 0 stub 0 nssa
 Number of areas transit capable is 0
 External flood list length 0
 IETF NSF helper support enabled
 Cisco NSF helper support enabled
 Reference bandwidth unit is 100 mbps

Device# show ospfv3

 OSPFv3 12 address-family ipv6
 Router ID 10.8.3.3
 Supports NSSA (compatible with RFC 3101)
 Supports Database Exchange Summary List Optimization (RFC 5243)
 Event-log enabled, Maximum number of events: 1000, Mode: cyclic
 Router is not originating router-LSAs with maximum metric
 Initial SPF schedule delay 5000 msecs
 Minimum hold time between two consecutive SPFs 10000 msecs
 Maximum wait time between two consecutive SPFs 10000 msecs
 Minimum LSA interval 5 secs
 Minimum LSA arrival 1000 msecs
 LSA group pacing timer 240 secs
 Interface flood pacing timer 33 msecs
 Retransmission pacing timer 66 msecs
 Retransmission limit dc 24 non-dc 24
 EXCHANGE/LOADING adjacency limit: initial 10, process maximum 50
 Number of external LSA 0. Checksum Sum 0x000000
 Number of areas in this router is 0. 0 normal 0 stub 0 nssa
 Graceful restart helper support enabled
 Reference bandwidth unit is 100 mbps
 RFC1583 compatibility enabled