1. WAN Backup Paul Flynn

2. 2 Dial Backup Mission-critical applications require additional WAN links in order to prevent downtime. Multiple T1s may be provisioned for a particular application and even backed up by a Frame Relay PVC. Although the additional lines may have been leased for backup purposes, these lines can also be used for load balancing or to route certain traffic. Strictly speaking, such links are extra links, not backup links.

3. 3 The primary link is typically a Frame Relay PVC, or a leased line. Backup interfaces can be a physical interface or a logical interface such as a dialer profile. Typical backup interfaces include Integrated Services Digital Network Basic rate Interface (ISDN BRI) and asynchronous interfaces. Serial interfaces connected to either an asynchronous modem or ISDN BRI can also be backup interfaces. The backup interface is also called the secondary link

4. 4 Configuring Backup

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6. 6 Backup Interface Options If a physical link is used as a backup to a primary connection, it is in standby mode and cannot be used as a link to another site. Next Slide illustrates a potential drawback of placing an interface in standby mode. Branch Office A wants to back up its Frame Relay connection with an ISDN BRI. However, Branch Office A also wants to use the same BRI interface as a DDR link to Branch Office B.

7. 7 If Branch Office A places the physical BRI link in standby mode, it is deactivated. The link does not activate until the primary line fails or reaches a specified threshold. Therefore, the BRI link cannot be used to connect to Branch Office B.

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9. 9 Dialer profiles and backup Configure one dialer profile to act as the backup line. This profile is in standby mode until engaged. Configure another dialer profile for DDR between the Branch Office A and Branch Office B. Then make the physical BRI interface a member of both dialer pools.

10. 10 When using a BRI for a dial backup, neither of the B channels can be used while the interface is in standby mode. When using dialer profiles, it is possible to have one B channel bound to the backup dialer profile and the other B channel bound to the DDR dialer profile at the same time.

11. 11 Configuring dial backups with dialer profiles 1.Create and configure a dialer interface. 2.Make the physical interface to be used as the backup, typically Bri 0/0, a member of the dialer pool by using the dialer pool-member number command.

12. 12 3. Configure the primary interface to use a backup: –Enter interface configuration mode for the primary interface. –Assign a Layer 3 address to the primary interface. –Specify the backup interface dialer to be used with the backup interface dialer number command.

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14. 14 Load backup with OSPF OSPF uses cost as the sole routing metric. Cost is based on bandwidth. For example, a 64-kbps link gets a metric of 1562, while a T1 link gets a metric of 64. Unless both the primary link and the secondary link have the same cost, OSPF will not install both routes in the routing table. If one link has a lower cost than the other, all routing occurs over the link with the lower cost, even if both lines are up.

15. 15 When the OSPF interface costs for the primary and secondary links are unequal, configure the costs to be the same by using the following command: Router(config-if)#ip ospf cost interface-cost The OSPF cost can be a value in the range from 1 to 65535.

16. 16 Load backup with IGRP and EIGRP With IGRP and EIGRP, unequal-cost load balancing can be configured. Use the variance multiplier command to configure unequal-cost load balancing by defining the difference between the best metric and the worst acceptable metric.

17. 17 Show Backup Commands

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19. 19 Floating static routes as backup

20. 20 Dialer watch The router monitors the existence of a specified route in the routing table. If that route is not present, the router initiates the dialup backup link. Unlike the other backup methods, such as backup interface or floating static routes, dialer watch does not require interesting traffic to trigger the dial.