3Com AccessBuilder 500 User Manual

Contents

3Com AccessBuilder 500 User Manual Manual pdf 64 page image

1-44 CHAPTER 1: GETTING STARTEDThere are some issues about which you should be aware whenimplementing an IP bridging solution.n Although calls to the remote site are only generated when data isaddressed to a specific IP host or hosts (in our example, 191.000.000.100),any data that cannot be identified as local is also passed over the linkwhile it is open. This can prevent the link from closing after the intendeddata has been transferred.n Some devices and applications (for example autodiscovery programson SNMP managers) poll all devices on a subnet at regular intervalsand this could lead to frequent ISDN calls if you have entered several IPhosts to generate autocalls to the remote site. When combined withthe problem described above, you could find your ISDN linepermanently connected.To avoid this situation you need to be sure that no devices or applicationsexist on your local site that could make unnecessary and costly calls to yourremote site. You can also configure the AccessBuilder 500 units at bothends of the link to implement a Firewall and/or Call Guillotine to reduce theamount of traffic permitted to pass across the link. See the AccessBuilderISDN Access Router Software Reference guide for more information aboutthese features.Alternatively, you may wish to configure the AccessBuilder 500 to operateas a router to prevent this problem occurring altogether. This howeverrequires that each site consists of separate subnets. See the next sectionfor more information about IP routing.IP Host on Another IP NetworkMost organizations using TCP/IP protocols on their network, choose tosubnet remote sites or even to have them on different networks. Thisrequires that connections to remote sites are routed rather than bridged.The advantage of routing over bridging is that calls to the remote site areonly made when data is specifically addressed to a remote network.Bridging passes any data not known to be for the local network to theremote network whether that is its destination or not.