This chapter describes how to use the IP tunneling. It includes the following sections:
Bridging IP Tunnel
Encapsulation and OSPF
Bridging IP Tunnel
Bridging IP tunnel is another feature of the ASRT bridging software. With the bridging tunnel feature enabled, the software encapsulates packets in TCP/IP packets. To the router, the packet looks like a TCP/IP packet. Once a frame is encapsulated in an IP envelope, the IP forwarder is responsible for selecting the appropriate network interface based on the destination IP address. This packet can be routed dynamically through large internetworks without degradation or network size restrictions.
The IP tunnel appears to the bridge as one of the bridge ports using IP as a means of input/output device. On the tunnel bridge port you can configure STB, SRB or SRT bridge behavior.
In SRB configuration, IP tunnel helps overcome the usual 7-hop distance limit encountered in source routing configurations. It also lets you connect source- routing end stations across non-source-routing media, such as Ethernet networks.
The bridging tunnel also reduces the large amounts of overhead that source routing causes in wide area networks (WANs)
Finally, it reduces source-routing's sensitivity to WAN faults and failures (if a path fails, all systems must restart their transmissions)
End stations see this path or tunnel, as a single hop, regardless of the complexity of the internetwork. Figure 8-1 shows an example of an IP internetwork using the tunnel feature in its configuration.
Figure 8-1 End Stations See Routing Across Complex IP Internet as One Hop
Encapsulation and OSPF
A major benefit of the encapsulation feature is the addition of the OSPF dynamic routing protocol to the routing process. OSPF offers the following benefits when used with encapsulation: