Cisco Systems 78-11741-02 manual Nhrp over ATM Example, IPC-53

Configuring IP Addressing

IP Addressing Examples

Figure 10 Physical Configuration of a Sample NBMA Network

Source host

Router A

Router E

Destination host

Router B

Router C

Router D

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Refer again to Figure 9. Initially, before NHRP has resolved any NBMA addresses, IP packets from the source host to the destination host travel through all five routers connected to the switch before reaching the destination. When Router A first forwards the IP packet toward the destination host, Router A also generates an NHRP request for the IP address of the destination host. The request is forwarded to Router C, whereupon a reply is generated. Router C replies because it is the egress router between the two logical NBMA networks.

Similarly, Router C generates an NHRP request of its own, to which Router E replies. In this example, subsequent IP traffic between the source and the destination still requires two hops to traverse the NBMA network, because the IP traffic must be forwarded between the two logical NBMA networks. Only one hop would be required if the NBMA network were not logically divided.

NHRP over ATM Example

The following example shows a configuration of three routers using NHRP over ATM. Subinterfaces and dynamic routing also are used. Router A obtains an OSPF route that it can use to reach the LIS where Router B resides. Router A can then initially reach Router B through Router C. Router A and Router B are able to directly communicate without Router C once NHRP has resolved the respective NSAP addresses of Router A and Router C.

Cisco IOS IP Configuration Guide

IPC-53