[ Pobierz całość w formacie PDF ]
.For example:interface serial 0description leased line from San Franciscoip address 128.10.200.65 255.255.255.192!interface serial 1description interface to answer backup calls from San Franciscoip address 128.10.200.129 255.255.255.192dialer in-band!router igrp 1network 128.10.0! route back to San Francisco with administrative distanceip route 128.10.0 255.255.0 128.10.200.130 150The first serial interface is the leased line, whereas the second answers calls from the central site incase the central site needs to use DDR as a backup method.2-24 Internetworking Case Studies Floating Static Routes on Shared InterfacesFloating Static Routes on Shared InterfacesThe central site configuration requires a large number of serial ports because each primary port hasits own backup.For true redundancy, backup is a requirement.But in many cases, an interface or aset of interfaces can be shared as backup for a set of primary lines.The following configurationshows how to set up a single interface to back up all of the primary lines:interface serial 1description Leased connection to Hong Kongip address 128.10.200.66 255.255.255.192!interface serial 2description leased connection to Singaporeip address 128.10.202.66 255.255.255.192!interface serial 5description backup DDR connection for all destinations except Tokyoip address 128.10.200.130 255.255.255.192ip address 128.10.202.130 255.255.255.192 secondarydialer in-banddialer wait-for-carrier-time 60! map Hong Kong to a phone numberdialer map ip 128.10.200.129 0118527351625! map Singapore to a phone numberdialer map ip 128.10.202.129 011653367085pulse-time 1dialer-group 1!interface serial 7description DDR connection to Tokyoip address 128.10.204.66 255.255.255.192dialer in-banddialer wait-for-carrier-time 60dialer string 0118127351625pulse-time 1dialer-group 1!router igrp 1network 128.10.0passive-interface serial 5redistribute static!! route to Hong Kong with administrative distanceip route 128.10.200.0 255.255.255.192 128.10.200.129 150! route to Singapore with administrative distanceip route 128.10.202.0 255.255.255.192 128.10.202.129 150! route to Tokyoip route 128.10.204.0 255.255.255.192 128.10.204.65!access-list 101 deny igrp 0.0 255.255.255.255 255.255.255.255 0.0access-list 101 permit ip 0.0 255.255.255.255 0.0 255.255.255.255dialer-list 1 list 101Serial interface 5 is the DDR backup interface for all destinations and is configured with multiple IPaddresses for routing.The dialer map commands map the next hop addresses to the telephonenumbers for each of the destinations.If a dynamic route is lost, the floating static route takes over.The next hop address sends the packets to serial interface 5, where the dialer map commands placethe telephone call.If two primary lines fail at the same time, there will be contention to use serial interface 5.Thefast-idle timer may disconnect the calls.If serial interface 5 were in constant use, one of the primarylines would be disconnected and packets would be dropped.The fact that the backup route isDial-on-Demand Routing 2-25 Using Leased Lines and Dial Backupunavailable is not communicated because there is no way to announce that one of the two IPaddresses on the interface are unavailable.If you use a dialer rotary group, the contention problemcan be avoided.Using Leased Lines and Dial BackupThis section describes how to use the following two methods for dial backup with leased lines:" DTR Dialing" V.25bis DialingDTR DialingSince Software Release 8.3, a dial backup capability has been provided.Although it is somewhatmore restrictive than floating static routes, dial backup can be used if V.25bis modems are notavailable or if protocols that do not have support for floating static routes are used.Central SiteDial backup requires that the modems place a call when the Data Terminal Ready (DTR) signal israised.The telephone number is configured into the modem or other DCE device.That number iscalled when DTR is raised.The call is disconnected when DTR is lowered.The followingconfiguration illustrates how to take advantage of dial backup and DTR dialing:interface serial 1description Leased connection to Hong Kongip address 128.10.200.66 255.255.255.192backup interface serial 4backup delay 0 20!interface serial 2description leased connection to Singaporeip address 128.10.202.66 255.255.255.192backup interface serial 5backup delay 0 20!interface serial 4description backup connection for Hong Kongip address 128.10.200.67 255.255.255.192pulse-time 10!interface serial 5description backup connection for Singaporeip address 128.10.202.67 255.255.255.192pulse-time 10!interface serial 7description DDR connection to Tokyoip address 128.10.204.66 255.255.255.192dialer in-banddialer wait-for-carrier-time 60dialer string 0118127351625pulse-time 1dialer-group 1!router igrp 1network 128.10
[ Pobierz całość w formacie PDF ]