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This feature module describes the ATM Routed Bridge Encapsulation feature and includes the following sections:
The ATM Routed Bridge Encapsulation feature is used to route IP over bridged RFC 1483 Ethernet traffic from a stub-bridged LAN.
Figure 1 shows an ATM subinterface on a head-end router, which is configured to function in ATM route-bridged encapsulation mode. This configuration is useful when a remote bridged Ethernet network device needs connectivity to a routed network via a device bridging from an Ethernet LAN to an ATM RFC 1483 bridged encapsulation.
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).
The ATM Routed Bridge Encapsulation feature reduces the security risk associated with normal bridging or IRB by reducing the size of the nonsecured network. By using a single virtual circuit (VC) allocated to a subnet (which could be as small as a single IP address), the ATM Routed Bridge Encapsulation feature uses IP address in the subnet to limit the "trust environment" to the premises of a single customer.
This feature does not support MAC-layer access lists. Only IP access lists are supported.
Standards
None
MIBs
No new or modified MIBs are supported by this feature. To obtain lists of MIBs supported by platform and Cisco IOS release and to download MIB modules, go to the Cisco MIB web site on Cisco Connection Online (CCO) at http://www.cisco.com/public/sw-center/netmgmt/cmtk/mibs.shtml.
RFCs
RFC 1483, Multiprotocol Encapsulation over ATM Adaptation Layer 5, July 1993
See the following sections for configuration tasks for the ATM Routed Bridge Encapsulation feature. Each task in this list is identified as optional or required.
To configure the ATM Routed Bridge Encapsulation feature, use the following commands beginning in global configuration mode:
| Command | Purpose | |
|---|---|---|
Step 1 | Router(config)# interface atm slot/0.subinterface-number point-to-point | Specifies an ATM point-to-point interface. |
Step 2 | Router(config-if)# pvc VPI/VCI | Configures a VC to carry the routed bridge traffic. |
Step 3 | Router(config-if)# atm route-bridge ip | Enables the ATM Routed Bridge Encapsulation feature for IP. |
Step 4 | Router(config-if)# ip address ip-address mask [secondary] | Provides an IP address on the same subnetwork as the remote network. |
Step 5 | Router(config-if)# ^Z | Exits 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, the ATM Routed Bridge Encapsulation feature can be used to route IP, while other protocols (such as IPX) are bridged normally.
To confirm that the ATM Routed Bridge Encapsulation feature is enabled, use the show arp command and the show ip cache verbose command:
pp4-72k1# show arp
Protocol Address Age (min) Hardware Addr Type Interface
Internet 10.1.0.51 6 0001.c9f2.a81d ARPA Ethernet3/1
Internet 10.1.0.49 - 0060.0939.bb55 ARPA Ethernet3/1
Internet 10.0.75.1 30 0010.0ba6.2020 ARPA Ethernet3/0
Internet 10.8.101.35 6 00e0.1e8d.3f90 ARPA ATM1/0.4
Internet 10.8.100.50 5 0007.144f.5d20 ARPA ATM1/0.2
Internet 10.0.75.49 - 0060.0939.bb54 ARPA Ethernet3/0
Internet 10.1.0.125 30 00b0.c2e9.bc55 ARPA Ethernet3/1
pp4-72k1#
pp4-72k1# show ip cache verbose
IP routing cache 3 entries, 572 bytes
9 adds, 6 invalidates, 0 refcounts
Minimum invalidation interval 2 seconds, maximum interval 5 seconds,
quiet interval 3 seconds, threshold 0 requests
Invalidation rate 0 in last second, 0 in last 3 seconds
Last full cache invalidation occurred 00:30:34 ago
Prefix/Length Age Interface Next Hop
10.1.0.51/32-24 00:30:10 Ethernet3/1 10.1.0.51
14 0001C9F2A81D00600939BB550800
10.8.100.50/32-24 00:00:04 ATM1/0.2 10.8.100.50
28 00010000AAAA030080C2000700000007144F5D2000600939
BB1C0800
10.8.101.35/32-24 00:06:09 ATM1/0.4 10.8.101.35
28 00020000AAAA030080C20007000000E01E8D3F9000600939
BB1C0800
pp4-72k1#
This section provides the following configuration examples:
The following example shows a typical ATM routed bridge encapsulation configuration:
interface atm 4/0.100 point-to-point ip address 172.16.5.9 255.255.255.0 pvc 0/32 atm route-bridge ip
The following 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-bridge ip ip route 172.16.5.9 255.255.255.0 interface atm 4/0.100
The following example shows concurrent use of ATM routed bridge encapsulation with normal bridging. IP datagrams are route-bridged and other protocols (such as IPX or AppleTalk) are bridged.
bridge 1 protocol ieee interface atm 4/0.100 point-to-point ip address 172.16.5.9 255.255.255.0 pvc 0/32 bridge-group 1 atm route-bridge ip
This section documents the atm route-bridge command. All other commands used with this feature are documented in the Cisco IOS Release 12.1 command references.
To configure an interface to use the ATM Routed Bridge Encapsulation feature, 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
12.0(5)DC This command was introduced. 12.1(2)T This command was migrated to the T train.
Release
Modification
Examples
The following example configures the ATM Routed Bridge Encapsulation feature on an interface:
interface atm 4/0.100 point-to-point ip address 172.16.5.9 255.255.255.0 pvc 0/32 atm route-bridge ip
bridge group—A group of interfaces bridged together to emulate a multiport bridge.
Bridge Group Virtual Interface—see BVI.
BVI—Bridge Group Virtual Interface. The logical Layer 3-only interface associated with a bridge group when IRB is configured.
integrated routing and bridging—see IRB.
IRB—integrated routing and bridging. The process of routing among a number of bridge groups.
routed bridge encapsulation—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.
Posted: Wed Sep 6 13:19:15 PDT 2000
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