Overview

Tunnels provide a way of transporting datagrams between routers separated by networks that do not support all the protocols that those routers support. (See Figure 2.)

Figure 2: Basic Components of a Tunnel

The NMC-RX application supports IP tunnel connections and SMDS tunnel connections. This chapter discusses both types of connections.

IP Tunnels

The E-series router supports static IP tunnels. An IP tunnel is a virtual point-to-point connection between two routers.

To establish an IP tunnel, you specify an IP tunnel type and name, and then specify an interface on each router to act as endpoints for the tunnel. (See Figure 3.)

Figure 3: Interface Column Components for an IP Tunnel

The E-series router supports the following IP tunnel types:

• Generic routing encapsulation (GRE)
• Distance Vector Multicast Routing Protocol (DVMRP)
  

  NOTE: Currently, the E-series router tunnels only IP packets.

  
  

SMDS Tunnels

The E-series router supports SMDS tunnels. The following components support the SMDS application:

• High-speed serial interface (HSSI) line module—Provides the physical interface to connect to the SMDS switch
• GRE tunnels—Transport SMDS traffic among E-series routers
• SMDS trunk interface—Runs over the HSSI line module and GRE tunnels
• Connection-based forwarding (CBF) interface—Forwards SMDS traffic among SMDS trunk interfaces

Figure 4 shows how these components make up the interface columns for the SMDS application.

Figure 4: Interface Columns for the SMDS Application

Two sets of interfaces are required for SMDS:

• The first set provides the connection between the E-series router and the SMDS switch. It has a physical HSSI line module on which you configure an SMDS trunk interface and a CBF interface.
• The second set provides the connection between E-series routers. It has a GRE tunnel, an SMDS trunk interface, and a CBF interface.

HSSI

The HSSI line module supports the SMDS trunk interface. This connection supports speeds of 34.368 or 44.736 Mbps.

GRE Tunnels

All SMDS traffic received on a HSSI must be mapped one-to-one with a specific GRE tunnel.

Line Modules

To create tunnels, you must install a Tunnel Service module in the E-series device. This module receives data from the ingress port and transmits data to other line modules from egress ports. You must assign IP tunnel interfaces to act as destination endpoints for the tunnel.

All line modules forward traffic to tunnels. The following line modules and their corresponding I/O modules accept traffic for tunnels:

• CE1
• cOCx/STMx
• CT1
• CT3
• E3 ATM and FRAME
• FE-2
• GE/FE
• OCx/STMx ATM and POS
• T3 ATM and FRAME