Cisco Commands - Revision history

50.220.241.211: /* Common OSPF Troubleshooting */

2026-10-22T01:08:07Z

Common OSPF Troubleshooting

← Older revision		Revision as of 01:08, 22 October 2026
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	==== Common OSPF Troubleshooting ====		==== Common OSPF Troubleshooting ====
	If OSPF neighbors or routes are missing, check the following:		If OSPF neighbors or routes are missing, check the following:


	* Verify that the correct interfaces have IP addresses and are up.		* Verify that the correct interfaces have IP addresses and are up.

50.220.241.211: /* Common OSPF Troubleshooting */

2026-10-22T01:08:02Z

Common OSPF Troubleshooting

← Older revision		Revision as of 01:08, 22 October 2026
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	If OSPF neighbors or routes are missing, check the following:		If OSPF neighbors or routes are missing, check the following:

	~~- Verify that the correct interfaces have IP addresses and are up.~~

	- Verify that ~~OSPF is enabled on~~ the ~~intended~~ interfaces.		* Verify that the correct interfaces have IP addresses and are up.

	~~- Check~~ the ~~area ID and hello/dead timers~~.		* Verify that OSPF is enabled on the intended interfaces.

	~~- Verify that router IDs are unique~~.		* Check the area ID and hello/dead timers.

	~~- Check passive-interface configuration~~.		* Verify that router IDs are unique.

	~~- Verify that the interfaces use compatible OSPF network types and authentication settings~~.		* Check passive*interface configuration.

	~~- Confirm~~ that the ~~required networks are advertised~~.		* Verify that the interfaces use compatible OSPF network types and authentication settings.

	~~- Check interface costs and~~ the ~~routing table~~.		* Confirm that the required networks are advertised.

	- Confirm that area 0 connectivity is correct in multiarea configurations.		* Check interface costs and the routing table.

			* Confirm that area 0 connectivity is correct in multiarea configurations.

	==== OSPFv2 and OSPFv3 ====		==== OSPFv2 and OSPFv3 ====

50.220.241.211: /* OSPFv2 and OSPFv3 */

2026-10-22T01:07:36Z

OSPFv2 and OSPFv3

← Older revision		Revision as of 01:07, 22 October 2026
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	==== OSPFv2 and OSPFv3 ====		==== OSPFv2 and OSPFv3 ====

	'''OSPFv2''' — Used for IPv4 routing.		*'''OSPFv2''' — Used for IPv4 routing.
			*'''OSPFv3''' — Originally designed for IPv6 routing and also supports address-family extensions for IPv4 on supported platforms.
	'''OSPFv3''' — Originally designed for IPv6 routing and also supports address-family extensions for IPv4 on supported platforms.

	IPv6 OSPFv3 configuration differs from OSPFv2. Interface-level commands and address-family configuration depend on the Cisco IOS version and platform.		IPv6 OSPFv3 configuration differs from OSPFv2. Interface-level commands and address-family configuration depend on the Cisco IOS version and platform.

50.220.241.211: /* OSPF Areas */

2026-10-22T01:07:02Z

OSPF Areas

← Older revision		Revision as of 01:07, 22 October 2026
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	OSPF divides a routing domain into areas to improve scalability and reduce the amount of routing information that must be processed by each router.		OSPF divides a routing domain into areas to improve scalability and reduce the amount of routing information that must be processed by each router.

	'''Area 0''' — The backbone area.		*'''Area 0''' — The backbone area.
			*'''Internal router''' — Has all OSPF interfaces within the same area.
	'''Internal router''' — Has all OSPF interfaces within the same area.		*'''Backbone router''' — Has at least one interface in area 0.
			*'''Area Border Router (ABR)''' — Connects multiple OSPF areas.
	'''Backbone router''' — Has at least one interface in area 0.		*'''Autonomous System Boundary Router (ASBR)''' — Redistributes routes from another routing source into OSPF.

	'''Area Border Router (ABR)''' — Connects multiple OSPF areas.

	'''Autonomous System Boundary Router (ASBR)''' — Redistributes routes from another routing source into OSPF.

	In a multiarea OSPF design, non-backbone areas must connect to area 0 logically, directly or through a supported virtual link.		In a multiarea OSPF design, non-backbone areas must connect to area 0 logically, directly or through a supported virtual link.

50.220.241.211: /* OSPF Neighbor Adjacencies */

2026-10-22T01:06:40Z

OSPF Neighbor Adjacencies

← Older revision		Revision as of 01:06, 22 October 2026
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	Important parameters include:		Important parameters include:
	- Area ID
	- Hello and dead intervals		* Area ID
	- Authentication settings, if configured		* Hello and dead intervals
	- Subnet and network compatibility		* Authentication settings, if configured
	- OSPF area type		* Subnet and network compatibility
	- Unique router IDs		* OSPF area type
			* Unique router IDs

	On broadcast networks, routers elect a Designated Router (DR) and Backup Designated Router (BDR) to reduce adjacency overhead. A point-to-point link does not elect a DR or BDR.		On broadcast networks, routers elect a Designated Router (DR) and Backup Designated Router (BDR) to reduce adjacency overhead. A point-to-point link does not elect a DR or BDR.

50.220.241.211: /* OSPF Network Types */

2026-10-22T01:06:05Z

OSPF Network Types

← Older revision		Revision as of 01:06, 22 October 2026
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	Common OSPF network types include:		Common OSPF network types include:

	'''Broadcast''' — Common on Ethernet LANs; supports DR/BDR elections.		*'''Broadcast''' — Common on Ethernet LANs; supports DR/BDR elections.

	'''Point-to-point''' — Common on direct router-to-router links; no DR/BDR election.		*'''Point-to-point''' — Common on direct router-to-router links; no DR/BDR election.

	'''Nonbroadcast multiaccess (NBMA)''' — Supports multiple routers without the usual broadcast behavior.		*'''Nonbroadcast multiaccess (NBMA)''' — Supports multiple routers without the usual broadcast behavior.

	The network type affects neighbor discovery and adjacency behavior.		The network type affects neighbor discovery and adjacency behavior.

50.220.241.211: /* Router ID Selection */

2026-10-22T01:04:09Z

Router ID Selection

← Older revision		Revision as of 01:04, 22 October 2026
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	If a router ID is not manually configured, Cisco IOS selects one using the following rules when OSPF starts:		If a router ID is not manually configured, Cisco IOS selects one using the following rules when OSPF starts:

	Use the highest IPv4 address configured on any active loopback interface.		*Use the highest IPv4 address configured on any active loopback interface.
	If no active loopback interface has an IPv4 address, use the highest IPv4 address on an active physical interface.		*If no active loopback interface has an IPv4 address, use the highest IPv4 address on an active physical interface.

	A manually configured router ID takes precedence over automatic selection.		A manually configured router ID takes precedence over automatic selection.

50.220.241.211: /* Router ID Selection */

2026-10-22T01:02:48Z

Router ID Selection

← Older revision		Revision as of 01:02, 22 October 2026
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	If a router ID is not manually configured, Cisco IOS selects one using the following rules when OSPF starts:		If a router ID is not manually configured, Cisco IOS selects one using the following rules when OSPF starts:

	Use the highest IPv4 address configured on any active loopback interface.		Use the highest IPv4 address configured on any active loopback interface.
	If no active loopback interface has an IPv4 address, use the highest IPv4 address on an active physical interface.		If no active loopback interface has an IPv4 address, use the highest IPv4 address on an active physical interface.

	A manually configured router ID takes precedence over automatic selection.		A manually configured router ID takes precedence over automatic selection.

50.220.241.211: /* Basic OSPF Configuration */

2026-10-22T01:01:12Z

Basic OSPF Configuration

← Older revision		Revision as of 01:01, 22 October 2026
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	<code>router ospf 1</code> — Starts OSPF process 1.		<code>router ospf 1</code> — Starts OSPF process 1.

	<code>network</code> — Identifies interfaces that participate in OSPF based on their IP addresses.		<code>network</code> — Identifies interfaces that participate in OSPF based on their IP addresses.

	<code>0.0.0.255</code> — Wildcard mask matching the 192.168.1.0/24 network.		<code>0.0.0.255</code> — Wildcard mask matching the 192.168.1.0/24 network.

	<code>area 0</code> — Places matching interfaces in OSPF backbone area 0.		<code>area 0</code> — Places matching interfaces in OSPF backbone area 0.

50.220.241.211: /* OSPF Areas */

2026-10-22T01:00:34Z

OSPF Areas

← Older revision		Revision as of 01:00, 22 October 2026
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	'''Area 0''' — The backbone area.		'''Area 0''' — The backbone area.

	'''Internal router''' — Has all OSPF interfaces within the same area.		'''Internal router''' — Has all OSPF interfaces within the same area.

	'''Backbone router''' — Has at least one interface in area 0.		'''Backbone router''' — Has at least one interface in area 0.

	'''Area Border Router (ABR)''' — Connects multiple OSPF areas.		'''Area Border Router (ABR)''' — Connects multiple OSPF areas.

	'''Autonomous System Boundary Router (ASBR)''' — Redistributes routes from another routing source into OSPF.		'''Autonomous System Boundary Router (ASBR)''' — Redistributes routes from another routing source into OSPF.