11-5 neighbor ip-address priority priority

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11-5 neighbor ip-address priority priority

Syntax Description:

  • ip-address ” IP address of the OSPF neighbor. If a secondary address is used on the interface, then the primary address must be used with this command because OSPF will only form an adjacency using the primary address.

  • priority ” The OSPF priority of the neighbor with the given IP address. The range of values is 0 to 255. The router with the lowest OSPF priority on a network will be elected the DR for the network. A priority of zero means that the router is not eligible to be elected the DR or Backup Designated Router (BDR). The default priority is 1.

Purpose: To influence the election of the DR. The router with the lowest non-zero priority will be elected the DR. In a hub and spoke topology, the hub router should be elected as the DR.

Initial Cisco IOS Software Release: 10.0

Configuration Example: Setting the Priority of an OSPF Neighbor

Configure the routers in Figure 11-8 as shown in the listing that follows .

Figure 11-8. The Election of the DR Can Be Influenced by Using the priority Option with the neighbor Router Configuration Command

graphics/11fig08.gif

 Router A  interface Loopback0   ip address 1.1.1.1 255.255.255.255   !   interface Serial0/0   bandwidth 64   ip address 10.1.1.1 255.255.255.252   encapsulation frame-relay   frame-relay map ip 10.1.1.2 101 broadcast   no frame-relay inverse-arp   frame-relay lmi-type ansi   !   router ospf 1   network 1.1.1.1 0.0.0.0 area 1   network 10.1.1.0 0.0.0.3 area 0  ________________________________________________________________ Router B  interface Loopback0   ip address 2.2.2.2 255.255.255.255   !   interface Serial0   ip address 10.1.1.2 255.255.255.252   encapsulation frame-relay   bandwidth 64   frame-relay map ip 10.1.1.1 110 broadcast   no frame-relay inverse-arp   frame-relay lmi-type ansi   !   router ospf 1   network 2.2.2.2 0.0.0.0 area 2   network 10.1.1.0 0.0.0.3 area 0    neighbor 10.1.1.1 priority 1   

Examine the state of the OSPF neighbors to determine which router has been elected the DR.

 rtrA#  show ip ospf neighbor  Neighbor ID     Pri   State           Dead Time   Address         Interface 2.2.2.2           1  FULL/BDR  00:01:45    10.1.1.2        Serial0/0 ______________________________________________________________________________________________________________ rtrB#  show ip ospf neighbor  Neighbor ID     Pri   State           Dead Time   Address         Interface 1.1.1.1           1  FULL/DR  00:01:37    10.1.1.1        Serial0 

Router A is the DR because it has a lower OSPF router ID. Modify the configuration on Router B so that it will be elected the DR. This can be accomplished by either setting the priority to 0 or larger than 1 in the neighbor statement.

 Router B  router ospf 1   network 2.2.2.2 0.0.0.0 area 2   network 10.1.1.0 0.0.0.3 area 0    neighbor 10.1.1.1 priority 2   

OSPF will not immediately elect a new DR. For stability reasons, OSPF will elect a new DR only if the current DR is down. Force the re-election of the DR by clearing the OSPF process on Router A.

 rtrA#  clear ip ospf process  Reset ALL OSPF processes? [no]:  y  rtrA# 
Verification

Verify that Router B has been elected as the DR.

 rtrA#  show ip ospf neighbor  Neighbor ID     Pri   State           Dead Time   Address         Interface 2.2.2.2           1  FULL/DR  00:01:45    10.1.1.2        Serial0/0 _____________________________________________________________________________________________________________ rtrB#  show ip ospf neighbor  Neighbor ID     Pri   State           Dead Time   Address         Interface 1.1.1.1           1   FULL/BDR        00:01:44    10.1.1.1        Serial0 
Troubleshooting
Step 1. The configured priority value will not take effect until the current DR is down and a new election takes place.

Step 2. Verify that the desired priority value has been used with the OSPF neighbor command.

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Cisco[r] OSPF Command and Configuration Handbook
Cisco OSPF Command and Configuration Handbook (paperback)
ISBN: 1587055406
EAN: 2147483647
Year: 2002
Pages: 236

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