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Cisco IOS Software Releases 12.0 Special and Early Deployments

ATM Routed Bridge Encaps

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Table of Contents

ATM Routed Bridge Encaps

Feature Overview

Supported Platforms

Supported Standards, MIBs, and RFCs

Configuration Tasks

Configuration Examples

Command Reference

Glossary

ATM Routed Bridge Encaps

Feature Overview

The ATM routed bridge encaps feature on the Cisco 6400 node route processor (NRP) is used to route IP over bridged RFC 1483 Ethernet traffic from a stub-bridged LAN.


Figure 1: ATM Routed Bridge Encaps

Bridged IP packets received on an ATM interface configured in route-bridged mode are routed via the IP header. Such interfaces take advantage of the characteristics of a stub LAN topology commonly used for digital subscriber line (DSL) access and offer increased performance and flexibility over integrated routing and bridging (IRB).

Benefits

Security

ATM routed bridge encaps reduces the security risk associated with normal bridging or IRB by reducing the size of the non-secured network. By using a single virtual circuit (VC) allocated to a subnet (which could be as small as a single IP address), ATM routed bridge encaps limits the "trust environment" to a single customer premises using IP addresses in the subnet.

Restrictions

ATM routed bridge encaps does not support MAC-layer access lists. Only IP access lists are supported.

Supported Platforms

ATM routed bridge encaps is supported on the Cisco 6400.

Supported Standards, MIBs, and RFCs

MIBs

None

RFCs
  • RFC 1483, Multiprotocol Encapsulation over ATM Adaptation Layer 5, July 1993

Standards

None

Configuration Tasks

Perform the following tasks to configure ATM routed bridge encaps. The first task is required; the remaining tasks are optional.

Configuring ATM Routed Bridge Encaps

Perform the following tasks to configure ATM routed bridge encaps on your Cisco 6400 NRP:

Step Command Purpose
1 .   


Router(config)# interface atm slot/0.subinterface-number 
point-to-point

Specify an ATM point-to-point interface.
2 .   


Router(config-if)# pvc VPI/VCI

Configure a VC to carry the routed bridge traffic.
3 .   


Router(config-if)# atm route-bridge ip

Enable ATM routed bridge encaps for IP.
4 .   


Router(config-if)# ip address ip-address mask 
[secondary]

Provide an IP address on the same subnetwork as the remote network.
5 .   


Router(config-if)# ^Z

Exit to EXEC mode.


Only the specified network layer (IP) will be routed. Any remaining protocols can be passed on to bridging or other protocols. In this manner, ATM routed bridge encaps can be used to route IP while other protocols (such as IPX) are bridged normally.

Verifying ATM Routed Bridge Encaps

Use the show ip cache command to confirm that ATM routed bridge encaps is enabled:

Router# show ip cache
IP routing cache version 4490, 141 entries, 20772 bytes, 0 hash overflows
Minimum invalidation interval 2 seconds, maximum interval 5 seconds,
   quiet interval 3 seconds, threshold 0 requests
Invalidation rate 0 in last 7 seconds, 0 in last 3 seconds
Last full cache invalidation occurred 0:06:31 ago
Prefix/Length       Age       Interface       MAC Header
131.108.1.1/32      0:01:09   Ethernet0/0     AA000400013400000C0357430800
131.108.1.7/32      0:04:32   Ethernet0/0     00000C01281200000C0357430800
131.108.1.12/32     0:02:53   Ethernet0/0     00000C029FD000000C0357430800
131.108.2.13/32     0:06:22   Fddi2/0         00000C05A3E000000C035753AAAA0300
                                              00000800
131.108.2.160/32    0:06:12   Fddi2/0         00000C05A3E000000C035753AAAA0300
                                              00000800
131.108.3.0/24      0:00:21   Ethernet1/2     00000C026BC600000C03574D0800
131.108.4.0/24      0:02:00   Ethernet1/2     00000C026BC600000C03574D0800
131.108.5.0/24      0:00:00   Ethernet1/2     00000C04520800000C03574D0800
131.108.10.15/32    0:05:17   Ethernet0/2     00000C025FF500000C0357450800
131.108.11.7/32     0:04:08   Ethernet1/2     00000C010E3A00000C03574D0800
131.108.11.12/32    0:05:10   Ethernet0/0     00000C01281200000C0357430800
131.108.11.57/32    0:06:29   Ethernet0/0     00000C01281200000C0357430800

Configuration Examples

This section provides the following configuration examples:

ATM Routed Bridge Encaps

The following example shows a typical ATM routed bridge encaps configuration:

interface atm 4/0.100 point-to-point
  ip address 172.69.5.9 255.255.255.0
  pvc 0/32
  atm route-bridged ip

ATM Routed Bridge Encaps on an Unnumbered Interface

The following ATM routed bridge encaps example uses a static route to point to an unnumbered interface:

interface atm 4/0.100 point-to-point
  ip unnumbered ethernet 1/0
  pvc 0/32
  atm route-bridged ip
 
ip route 172.69.5.9 255.255.255.0 interface atm 4/0.100

Concurrent Bridging and ATM Routed Bridge Encaps

The following example shows concurrent use of ATM routed bridge encaps with normal bridging. IP datagrams are route-bridged, while other protocols (such as IPX or AppleTalk) are bridged.

bridge 1 protocol ieee
 
interface atm 4/0.100 point-to-point
  ip address 172.69.5.9 255.255.255.0
  pvc 0/32
  bridge-group 1
  atm route-bridged ip

Command Reference

This section documents new commands. All other commands used with this features are documented in the Cisco IOS Release 12.0 command references.

atm route-bridge

To configure an interface to use ATM routed bridge encaps, use the atm route-bridge interface configuration command.

atm route-bridge protocol

Syntax Description

protocol

Protocol to be route-bridged.

Defaults

No default behavior or values.

Command Modes

Interface configuration

Command History

Release Modification

12.0(5)DC

This command was first introduced.

Examples

The following example configures ATM routed bridge encaps on an interface:

interface atm 4/0.100 point-to-point
  ip address 172.69.5.9 255.255.255.0
  pvc 0/32
  atm route-bridged ip

Glossary

bridge-group---A group of interfaces bridged together to emulate a multi-port bridge.

BVI---Bridge Virtual Interface. The logical Layer 3-only interface associated with a bridge-group when IRB is configured.

NRP---node route processor. One of the component modules used in the Cisco 6400. This module is the Layer 3 element for the Cisco 6400 responsible for implementing the routing function.

routed bridge encaps---The process by which a stub-bridged segment is terminated on a point-to-point routed interface. Specifically, the router is routing on an IEEE 802.3 or Ethernet header carried over a point-to-point protocol such as PPP, RFC 1483 ATM, or RFC 1490 Frame Relay.

IRB---integrated routing and bridging. The process of routing between a number of bridge-groups.

U interface---The interface between the telco and the user, also known as the local digital subscriber line (DSL) loop.