Prefix Suppression Support for OSPFv3

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Before you can use the mechanism to exclude IPv4 and IPv6 prefixes from LSAs, the OSPFv3 routing protocol must be configured.

The OSPFv3 Prefix Suppression Support feature allows you to hide IPv4 and IPv6 prefixes that are configured on interfaces running OSPFv3.

In OSPFv3, addressing semantics have been removed from the OSPF protocol packets and the main LSA types, leaving a network-protocol-independent core. This means that Router-LSAs and network-LSAs no longer contain network addresses, but simply express topology information. The process of hiding prefixes is simpler in OSPFv3 and suppressed prefixes are simply removed from the intra-area-prefix-LSA. Prefixes are also propagated in OSPFv3 via link LSAs

The OSPFv3 Prefix Suppression feature provides a number of benefits.The exclusion of certain prefixes from adverstisements means that there is more memory available for LSA storage, bandwidth and buffers for LSA flooding, and CPU cycles for origination and flooding of LSAs and for SPF computation. Prefixes are also filtered from link LSAs. A device only filters locally configured prefixes, not prefixes learnt via link LSAs. In addition, security has been improved by reducing the possiblity of remote attack with the hiding of transit-only networks.

You can reduce OSPFv3 convergence time by configuring the OSPFv3 process on a device to prevent the advertisement of all IPv4 and IPv6 prefixes by using the prefix-suppression command in router configuration mode or address-family configuration mode.

Note	Prefixes that are associated with loopbacks, secondary IP addresses, and passive interfaces are not suppressed by the router mode or the address-family configuration commands because typical network designs require prefixes to remain reachable.

SUMMARY STEPS

1.    enable

2.    configure terminal

3.    router ospfv3 process-id [vrf vpn-name]

4.    prefix-suppression

5.    end

6.    show ospfv3

DETAILED STEPS

	Command or Action	Purpose
Step 1	enable Example: Device> enable	Enables privileged EXEC mode. Enter your password if prompted.
Step 2	configure terminal Example: Device# configure terminal	Enters global configuration mode.
Step 3	router ospfv3 process-id [vrf vpn-name] Example: Device(config)# router ospfv3 23	Configures an OSPFv3 routing process and enters router configuration mode.
Step 4	prefix-suppression Example: Device(config-router)# prefix-suppression	Prevents OSPFv3 from advertising all IPv4 and IPv6 prefixes, except prefixes that are associated with loopbacks, secondary IP addresses, and passive interfaces.
Step 5	end Example: Device(config-router)# end	Returns to privileged EXEC mode.
Step 6	show ospfv3 Example: Device# show ospfv3	Displays general information about OSPFv3 routing processes. Note    Use this command to verify that IPv4 and IPv6 prefix suppression has been enabled.

SUMMARY STEPS

1.    enable

2.    configure terminal

3.    router ospfv3 process-id [vrf vpn-name]

4.    address-family ipv6 unicast

5.    prefix-suppression

6.    end

7.    show ospfv3

DETAILED STEPS

	Command or Action	Purpose
Step 1	enable Example: Device> enable	Enables privileged EXEC mode. Enter your password if prompted.
Step 2	configure terminal Example: Device# configure terminal	Enters global configuration mode.
Step 3	router ospfv3 process-id [vrf vpn-name] Example: Device(config)# router ospfv3 23	Configures an OSPFv3 routing process and enters router configuration mode.
Step 4	address-family ipv6 unicast Example: Device(config-router)# address-family ipv6 unicast	Enters IPv6 address family configuration mode for OSPFv3.
Step 5	prefix-suppression Example: Device(config-router-af)# prefix-suppression	Prevents OSPFv3 from advertising all IPv4 and IPv6 prefixes, except prefixes that are associated with loopbacks, secondary IP addresses, and passive interfaces.
Step 6	end Example: Device(config-router-af)# end	Returns to privileged EXEC mode.
Step 7	show ospfv3 Example: Device# show ospfv3	Displays general information about OSPFv3 routing processes. Note    Use this command to verify that IPv4 and IPv6 prefix suppression has been enabled.

SUMMARY STEPS

1.    enable

2.    configure terminal

3.    interface type number

4.   Do one of the following:

5.    end

6.    show ospfv3 interface

DETAILED STEPS

	Command or Action	Purpose
Step 1	enable Example: Device> enable	Enables privileged EXEC mode. Enter your password if prompted.
Step 2	configure terminal Example: Device# configure terminal	Enters global configuration mode.
Step 3	interface type number Example: Device(config)# interface serial 0/0	Configures an interface type and enters interface configuration mode.
Step 4	Do one of the following: ipv6 ospf prefix-suppression [disable] ospfv3 prefix-suppression disable Example: Device(config-if)# ipv6 ospf prefix-suppression Example: Device(config-if)# ospfv3 1 prefix-suppression disable	Prevents OSPFv3 from advertising IPv4 and IPv6 prefixes that belong to a specific interface, except those that are associated with secondary IP addresses. When you enter the ipv6 ospf prefix-suppression command or the ospfv3 prefix-suppression command in interface configuration mode, it takes precedence over the prefix-suppression command that is entered in router configuration mode.
Step 5	end Example: Device(config-if)# end	Returns to privileged EXEC mode.
Step 6	show ospfv3 interface Example: Device# show ospfv3 interface	Displays OSPFv3-related interface information. Note    Use this command to verify that IPv4 and IPv6 prefix suppression has been enabled for a specific interface.

SUMMARY STEPS

1.    enable

2.    debug ospfv3 lsa-generation

3.    debug condition interface interface-type interface-number [dlci dlci] [vc {vci | vpi | vci}]

4.    show debugging

5.    show logging [slot slot-number | summary]

DETAILED STEPS

	Command or Action	Purpose
Step 1	enable Example: Device> enable	Enables privileged EXEC mode. Enter your password if prompted.
Step 2	debug ospfv3 lsa-generation Example: Device# debug ospfv3 lsa-generation	Displays informations about each OSPFv3 LSA that is generated.
Step 3	debug condition interface interface-type interface-number [dlci dlci] [vc {vci | vpi | vci}] Example: Device# debug condition interface serial 0/0	Limits output for some debug commands on the basis of the interface or virtual circuit.
Step 4	show debugging Example: Device# show debugging	Displays information about the types of debugging that are enabled for your device.
Step 5	show logging [slot slot-number | summary] Example: Device# show logging	Displays the state of syslog and the contents of the standard system logging buffer.