解决可达性问题-CCNA中文版PPT下载

解决可达性问题 水平分割在NBMA环境中导致问题,子接口可以解决水平分隔的问题 ,单个物理接口模拟多个逻辑接口。 Subnet A Subnet B Subnet C S0 物理接口 划分子接口 S0.1 S0.2 S0.3 * Purpose: This figure defines subinterfaces and how they can resolve NBMA issues. Emphasize: You can have connectivity problems in a Frame Relay network if these conditions exist: You are using an NBMA model. Your configuration is in a partial mesh. You are using a distance vector routing protocol. Split horizon is enabled on the routing protocol. If the routing protocol is configured with split horizon, routing updates from one router connected on the multipoint subinterface are not propagated to other routers connected on this multipoint subinterface. For example, if router C sends a routing update, this split horizon will keep this update from being sent back out the subinterface to router D. To resolve this problem you can: Use Frame Relay subinterfaces to overcome the split horizon problem. Use a routing protocol that supports disabling split horizon. Use this configuration if you want to save IP address space. You can also use this type of configuration with several fully meshed groups. Routing updates will be exchanged between the fully meshed routers. Note: When an interface is assigned “encapsulation frame-relay,” split horizon is disabled for IP and enabled for IPX and AppleTalk, by default.