Module 3– Virtual-links ppt

OSPF Virtual Links OSPF includes the concept of virtual links.. Virtual links mend the OSPF backbone area area 0..  The backbone should never be intentionally partitioned, but if part

BSCI Module 3 Lesson 8 – Virtual-links

 OSPF Virtual Links

 Configuring Virtual Links

 Virtual Link Configuration Example

 Verifying a Virtual Link Configuration

OSPF Virtual Links

 OSPF includes the concept of virtual links Virtual links mend the OSPF

backbone area (area 0)

 The backbone should never be intentionally partitioned, but if partitioning

occurs, consider using a virtual link to temporarily repair the backbone area

 Virtual links are logical connections that are vaguely analogous to a

tunnel Virtual links are not a true tunnel in the sense that one protocol is encapsulated by another.

 You can use a virtual link in the following cases:

– Area 0 becomes partitioned

– A nonbackbone area does not have a physical connection to area 0

OSPF Virtual Links

Virtual Links

 Virtual links are used to connect a discontiguous area

to area 0.

 A logical connection is built between router A and

router B.

 Virtual links are recommended for backup or temporary

connections.

Special Treatment for LSAs on Virtual Links

 LSAs usually age out after 30 minutes

 LSAs learned across virtual links have the DoNotAge

(DNA) option set

 Required to prevent excessive flooding over virtual links

Configuring Virtual Links

 Creates a virtual link

 Optional parameters are used in place of interface

ip ospf commands

area area-id virtual-link router-id

Router(config-router)#

RouterA# sh ip ospf virtual-links

Virtual Link OSPF_VL0 to router 10.2.2.2 is up Run as demand circuit

DoNotAge LSA allowed.

Transit area 1, via interface Serial0/0/1, Cost of using 781 Transmit Delay is 1 sec, State POINT_TO_POINT,

Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5 Hello due in 00:00:07

Adjacency State FULL (Hello suppressed) Index 1/2, retransmission queue length 0, number of retransmission 1 First 0x0(0)/0x0(0) Next 0x0(0)/0x0(0)

Last retransmission scan length is 1, maximum is 1 Last retransmission scan time is 0 msec, maximum is 0 msec

Configuring and Verifying a Virtual Link

Activity

Self Check

1 List 2 situation need to use Virtual Link

2 Area 0 virtual-link …… ?

 Virtual-Link

Q and A

 OSPF Virtual Link

– http://www.cisco.com/en/US/tech/tk365/technologies_configur ation_example09186a00801ec9ee.shtml

 What Are OSPF Areas and Virtual Links?

– http://www.cisco.com/en/US/tech/tk365/technologies_tech_not e09186a0080094aaa.shtml

 Configuring OSPF Authentication on a Virtual Link

– http://www.cisco.com/en/US/tech/tk365/technologies_configur ation_example09186a00800946bd.shtml