© 2008 Cisco Systems, Inc. All rights reserved. Cisco ConfidentialBSCI 1 BSCI Module 3 Lesson 8 – Virtual-links OSPF © 2008 Cisco Systems, Inc. All rights reserved.BSCI 2 CCNP – BSCI Bachkhoa Networking Academy Học viện mạng Bách Khoa - www.bkacad.com Objective OSPF Virtual Links Configuring Virtual Links Virtual Link Configuration Example Verifying a Virtual Link Configuration © 2008 Cisco Systems, Inc. All rights reserved.BSCI 3 CCNP – BSCI Bachkhoa Networking Academy Học viện mạng Bách Khoa - www.bkacad.com 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 © 2008 Cisco Systems, Inc. All rights reserved.BSCI 4 CCNP – BSCI Bachkhoa Networking Academy Học viện mạng Bách Khoa - www.bkacad.com OSPF Virtual Links © 2008 Cisco Systems, Inc. All rights reserved.BSCI 5 CCNP – BSCI Bachkhoa Networking Academy Học viện mạng Bách Khoa - www.bkacad.com 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. © 2008 Cisco Systems, Inc. All rights reserved.BSCI 6 CCNP – BSCI Bachkhoa Networking Academy Học viện mạng Bách Khoa - www.bkacad.com 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 © 2008 Cisco Systems, Inc. All rights reserved.BSCI 7 CCNP – BSCI Bachkhoa Networking Academy Học viện mạng Bách Khoa - www.bkacad.com 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)# © 2008 Cisco Systems, Inc. All rights reserved.BSCI 8 CCNP – BSCI Bachkhoa Networking Academy Học viện mạng Bách Khoa - www.bkacad.com 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 © 2008 Cisco Systems, Inc. All rights reserved.BSCI 9 CCNP – BSCI Bachkhoa Networking Academy Học viện mạng Bách Khoa - www.bkacad.com Activity © 2008 Cisco Systems, Inc. All rights reserved.BSCI 10 CCNP – BSCI Bachkhoa Networking Academy Học viện mạng Bách Khoa - www.bkacad.com Self Check 1. List 2 situation need to use Virtual Link 2. Area 0 virtual-link ……. ? . © 2008 Cisco Systems, Inc. All rights reserved. Cisco ConfidentialBSCI 1 BSCI Module 3 Lesson 8 – Virtual-links OSPF © 2008 Cisco Systems, Inc. All rights reserved.BSCI 2 CCNP – BSCI. – BSCI Bachkhoa Networking Academy Học viện mạng Bách Khoa - www.bkacad.com RouterA#sh ip ospf virtual-links Virtual Link OSPF_VL0 to router 10.2.2.2 is up Run as demand circuit DoNotAge LSA