Document ID: 25086
Contents
Introduction
It is now possible to configure a Cisco Catalyst 8540MSR as a ATM Label Edge Router (ATM LER) with the Cisco IOS®
Software version 12.1(10)EY. Previously, a Catalyst 8540MSR could only be configured as ATM Label Switch Router (ATM LSR). In other words, there were only "transit" VCs on a Catalyst 8540. As a result, a this device could not be at the head-end of a cell-based Label Switched path. That functionality had to be performed by other kinds of routers, such as the 7500.
The Catalyst 8540 can now be installed at the edge of a cell-based Multiprotocol Label Switching (MPLS) network. In order to achieve such functionality, it is necessary to use an Enhanced ATM Router Module (ARM) (also known as ARM2). The ARM2 acts as a "proxy" interface for every incoming and outgoing ATM interface (that is linked to an Enhanced ATM router module using the mpls-forwarding command) to do the MPLS packet processing.
This feature has some limitations:
- The ATM interface (main interface) can only be linked with the enhanced ATM router module main interface.
- VRF configuration on ATM OC-x interfaces is not supported.
- The class of service (CoS), label forwarding information base (LFIB) , and Label region in the Switching Database Manager (SDM) can be modified using the sdm sram command. But, the changes only take effect after a switch reload.
- Load Balancing between provider edge (PE) and provider (P) switches is not supported.
- Forwarding of VPN traffic is based only on the VPN routing table and not on the global routing table. If the VPN routing table lookup fails, the packets will be discarded.
- The Enhanced ATM router module internal link has a maximum capacity of 1.2 Gbps which could affect the number of interfaces associated with the Enhanced ATM router module.
- Only 2k terminating TAG VCs are supported per controlling Enhanced ATM router module hardware interface.
- Fragmentation based on MTU for IP to MPLS and MPLS to MPLS traffic is implemented in the route processors not on the interface modules.
Network Diagram
The following network topology will be used to illustrate this document.- Procida is a Catalyst 8540MSR running Cisco IOS® Software Release 12.1(10)EY and has an Enhanced ATM Router Module in slot 10 as can be seen in the show hardware output below.
- Bernard is a Cisco 7505 router running Cisco IOS Software Release 12.2(8)T with a PA-A.
- Fernet is a Cisco 2620 and Router is a Cisco 3620 used to inject routes to Bernard.
Fernet and Router are two CE routers. Procida acts as PE router and Bernard is a 7500 router.Procida#show hardware C8540 named Procida, Date: 04:23:57 UTC Wed May 22 2002 Slot Ctrlr-Type Part No. Rev Ser No Mfg Date RMA No. Hw Vrs Tst EEP ---- ------------ ---------- -- -------- --------- -------- ------- --- --- 2/* Super Cam 73-2739-03 B0 03170TC6 Apr 27 99 0 3.0 2/0 155MM PAM 73-1496-03 A0 10988822 Dec 09 98 00-00-00 3.2 0 2 10/* CMPM Card 73-3944-05 A0 04209F5M Aug 31 00 0 5.0 10/0 ARM2 PAM 73-5533-01 A0 0424A16L Aug 31 00 0 5.1 10/1 ARM2 PAM 73-5533-01 A0 0424A17V Aug 31 00 0 5.1 12/* ETHERNET PAM 73-3754-04 A0 0246013S Nov 19 98 0 3.2
Configurations
For clarity purposes, only the configurations of Procida and Bernard will be shown.
Quick Configuration Guide
- Set up your network as usual (MPLS needs a standard IP connection in order to establish forwarding bases).
- Ensure that the routing protocol (in this case OSPF) is working correctly.
- Enable ip cef (for better performances use ip cef distributed when available) in the general configuration mode (shown in bold in the following configurations).
- Enable tag-switching ip (or mpls ip on newer IOS versions) in the ATM interface (shown in bold in the following configurations).
Procida
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ip cef ! interface FastEthernet12/0/0 ip address 20.1.1.2 255.255.255.0 ! interface ATM10/0/0 no shutdown ! interface ATM2/0/1 ip address 20.2.2.1 255.255.255.0 logging event subif-link-status no atm ilmi-keepalive tag-switching ip mpls-forwarding interface ATM10/0/0 ! router ospf 1 log-adjacency-changes network 20.1.1.0 0.0.0.255 area 0 network 20.2.2.0 0.0.0.255 area 0 |
Bernard
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ip cef ! interface ATM3/0/0.1 tag-switching ip address 20.2.2.2 255.255.255.0 no ip directed-broadcast no atm enable-ilmi-trap tag-switching ip ! interface FastEthernet3/1/0 ip address 20.3.3.1 255.255.255.0 ! router ospf 1 log-adjacency-changes network 20.2.2.0 0.0.0.255 area 0 network 20.3.3.0 0.0.0.255 area 0 |
Configuration Task for the 8540MSR
As mentioned in the introduction, in order to act as an ATM LER, the ATM interfaces used in the MPLS forwarding must be configured for MPLS first and then linked to one of the ARM ATM interfaces using the mpls-forwarding interface atm x/y/z command.
Note: Make sure that the ARM ATM interface used is up before configuring the mpls-forwarding command. In this case, the interface atm 2/0/1 is linked to the ARM interface atm 10/0/0.
Once MPLS is enabled on an ATM interface and the interface is linked to the enhanced ATM router module, all head-end, control, and tail-end VCs through that ATM interface terminate on the Enhanced ATM router module. All MPLS or IP packet processing is performed on the linked Enhanced ATM router module.
Show Commands
The show commands most commonly used for this type of configuration are:
- show ip route
- show tag-switching tdp neighbor
- show tag-switching forwarding-table
- show tag-switching bindings
- show ip cef
Procida#show ip route Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2 E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area * - candidate default, U - per-user static route, o - ODR P - periodic downloaded static route Gateway of last resort is 10.48.72.1 to network 0.0.0.0 4.0.0.0/32 is subnetted, 1 subnets C 4.4.4.4 is directly connected, Loopback0 20.0.0.0/24 is subnetted, 3 subnets O 20.3.3.0 [110/2] via 20.2.2.2, 01:39:20, ATM2/0/1 C 20.2.2.0 is directly connected, ATM2/0/1 C 20.1.1.0 is directly connected, FastEthernet12/0/0 7.0.0.0/32 is subnetted, 1 subnets O 7.0.0.1 [110/3] via 20.2.2.2, 01:39:20, ATM2/0/1 8.0.0.0/32 is subnetted, 1 subnets O 8.0.0.1 [110/3] via 20.2.2.2, 01:39:20, ATM2/0/1 9.0.0.0/32 is subnetted, 1 subnets O 9.0.0.1 [110/3] via 20.2.2.2, 01:39:21, ATM2/0/1
Use the show tag-switching tdp * commands to verify the state of TDP. View neighbors by using the show tag-switching tdp neighbor command:
Procida#show tag-switching tdp neighbor Peer TDP Ident: 20.3.3.1:1; Local TDP Ident 4.4.4.4:2 TCP connection: 20.2.2.2.11005 - 20.2.2.1.711 State: Oper; PIEs sent/rcvd: 13/13; Downstream on demand Up time: 00:05:57 TDP discovery sources: ATM2/0/1, Src IP addr: 20.2.2.2
The tag-switching forwarding table is the label switching equivalent of the IP routing table for standard IP routing. It contains incoming and outgoing labels and descriptions of the packets. You can check it by using the show tag-switching forwarding-table command:
Procida#show tag-switching forwarding-table Local Outgoing Prefix Bytes tag Outgoing Next Hop tag tag or VC or Tunnel Id switched interface 16 51 20.3.3.0/24 0 AT2/0/1 point2point 17 48 7.0.0.1/32 0 AT2/0/1 point2point 18 49 8.0.0.1/32 0 AT2/0/1 point2point 19 50 9.0.0.1/32 0 AT2/0/1 point2point
Use the show tag-switching atm-tdp bindings to display the requested entries from the ATM TDP tag binding database.
Procida#show tag-switching atm-tdp bindings Destination: 7.0.0.1/32 Headend Switch ATM2/0/1 (2 hops) 1/33 Active, VCD=48 Destination: 8.0.0.1/32 Headend Switch ATM2/0/1 (2 hops) 1/34 Active, VCD=49 Destination: 9.0.0.1/32 Headend Switch ATM2/0/1 (2 hops) 1/35 Active, VCD=50 Destination: 20.3.3.0/24 Headend Switch ATM2/0/1 (2 hops) 1/36 Active, VCD=51 Destination: 20.1.1.0/24 Tailend Switch ATM2/0/1 1/33 Active -> Terminating Active, VCD=52Procida#show ip cef 20.1.1.1 20.1.1.1/32, version 40, connected, cached adjacency 20.1.1.1 0 packets, 0 bytes via 20.1.1.1, FastEthernet12/0/0, 0 dependencies next hop 20.1.1.1, FastEthernet12/0/0 valid cached adjacencyProcida#show ip cef 7.0.0.1 7.0.0.1/32, version 50, cached adjacency to ATM2/0/1 0 packets, 0 bytes tag information set local tag: 17 fast tag rewrite with AT2/0/1, point2point, tags imposed: {48(vcd=48)} via 20.2.2.2, ATM2/0/1, 0 dependencies next hop 20.2.2.2, ATM2/0/1 valid cached adjacency tag rewrite with AT2/0/1, point2point, tags imposed: {48(vcd=48)} Procida#show atm vc interface atm 2/0/1 Interface VPI VCI Type X-Interface X-VPI X-VCI Encap Status ATM2/0/1 0 5 PVC ATM0 0 44 QSAAL UP ATM2/0/1 0 16 PVC ATM0 0 37 ILMI UP ATM2/0/1 0 32 PVC ATM10/0/0 2 42 SNAP UP ATM2/0/1 1 33 TVC(O) ATM10/0/0 2 48 MUX UP ATM2/0/1 1 33 TVC(I) ATM10/0/0 2 52 MUX UP ATM2/0/1 1 34 TVC(O) ATM10/0/0 2 49 MUX UP ATM2/0/1 1 35 TVC(O) ATM10/0/0 2 50 MUX UP ATM2/0/1 1 36 TVC(O) ATM10/0/0 2 51 MUX UP
Example
The following example is based on the outputs above. Upon reception of a packet destined for 7.0.0.1 on the interface fast-ethernet 12/0/0, the 8540 (Procida) will forward the packet to the controlling ARM2 interface (atm10/0/0) which in turn sends the packet on to the appropriate Tag VC (TVC) (in this case 2/48) which is then switched by the fabric to the TVC 1/33 on atm 2/0/1 (as shown in the output above). Upon reception of a packet for 20.1.1.1 on the interface atm 2/0/1, this packet will be forwarded to the controlling ARM2 which in turn forwards it to the appropriate interface. The Enhanced ARM interface is acting as a "proxy" interface.
Related Information
- MPLS over ATM: VC Merge
- Understanding Session Establishment and Route Exchange in an MPLS-Enabled
- Understanding Multiprotocol Label Switching (MPLS) Label Imposition in an ATM
- Implementing MPLS with the Cisco Catalyst 8540
- Configuring Basic MPLS Using OSPF
- Configuring MPLS over RFC1483 PVCs on the Enhanced ATM Router Module (ARM)
Additional Links
- More ATM Information
- MPLS over ATM Home Page
- Technical Support - Cisco Systems
- Tools and Utilities - Cisco Systems
| Updated: Dec 18, 2007 | Document ID: 25086 |