Catalyst 4500 Series Switch Software Configuration Guide, Release IOS XE 3.3(0)XO

Configuring VRF-lite

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Virtual Private Networks (VPNs) provide a secure way for customers to share bandwidth over an ISP backbone network. A VPN is a collection of sites sharing a common routing table. A customer site is connected to the service provider network by one or more interfaces, and the service provider associates each interface with a VPN routing table. A VPN routing table is called a VPN routing/forwarding (VRF) table.

With the VRF-lite feature, the Catalyst 4500 series switch supports multiple VPN routing/forwarding instances in customer edge devices. (VRF-lite is also termed multi-VRF CE, or multi-VRF Customer Edge Device). VRF-lite allows a service provider to support two or more VPNs with overlapping IP addresses using one interface.

Note The Catalyst 4500 switch supports VRF lite NSF support with routing protocols OSPF/EIGRP/BGP.

Note The switch does not use Multiprotocol Label Switching (MPLS) to support VPNs. For information about MPLS VRF, refer to the Cisco IOS Switching Services Configuration Guide at:

http://www.cisco.com/en/US/docs/ios/mpls/configuration/guide/mp_vpn_ipv4_ipv6_ps6922_TSD_Products_Configuration_Guide_Chapter.html

This chapter includes these topics:

• About VRF-lite
• Default VRF-lite Configuration
• VRF-lite Configuration Guidelines
• Configuring VRFs
• Configuring VRF-Aware Services
• Configuring Per-VRF for TACACS+ Servers
• Configuring Multicast VRFs
• Configuring a VPN Routing Session
• Configuring BGP PE to CE Routing Sessions
• VRF-lite Configuration Example
• Displaying VRF-lite Status

Note For complete syntax and usage information for the switch commands used in this chapter, first look at the Cisco Catalyst 4500 Series Switch Command Reference and related publications at this location:

http://www.cisco.com/en/US/products//hw/switches/ps4324/index.html

If the command is not found in the Catalyst 4500 Series Switch Command Reference, it will be found in the larger Cisco IOS library. Refer to the Cisco IOS Command Reference and related publications at this location:

http://www.cisco.com/en/US/products/ps6350/index.html

About VRF-lite

VRF-lite is a feature that enables a service provider to support two or more VPNs, where IP addresses can be overlapped among the VPNs. VRF-lite uses input interfaces to distinguish routes for different VPNs and forms virtual packet-forwarding tables by associating one or more Layer 3 interfaces with each VRF. Interfaces in a VRF can be either physical, such as Ethernet ports, or logical, such as VLAN SVIs, but a Layer 3 interface cannot belong to more than one VRF at any time.

Note VRF-lite interfaces must be Layer 3 interfaces.

VRF-lite includes these devices:

• Customer edge (CE) devices provide customer access to the service provider network over a data link to one or more provider edge routers. The CE device advertises the site’s local routes to the provider edge router and learns the remote VPN routes from it. A Catalyst 4500 series switch can be a CE.
• Provider edge (PE) routers exchange routing information with CE devices by using static routing or a routing protocol such as BGP, RIPv1, or RIPv2.

The PE is only required to maintain VPN routes for those VPNs to which it is directly attached, eliminating the need for the PE to maintain all of the service provider VPN routes. Each PE router maintains a VRF for each of its directly connected sites. Multiple interfaces on a PE router can be associated with a single VRF if all of these sites participate in the same VPN. Each VPN is mapped to a specified VRF. After learning local VPN routes from CEs, a PE router exchanges VPN routing information with other PE routers by using internal BGP (iBPG).

• Provider routers (or core routers) are any routers in the service provider network that do not attach to CE devices.

With VRF-lite, multiple customers can share one CE, and only one physical link is used between the CE and the PE. The shared CE maintains separate VRF tables for each customer and switches or routes packets for each customer based on its own routing table. VRF-lite extends limited PE functionality to a CE device, giving it the ability to maintain separate VRF tables to extend the privacy and security of a VPN to the branch office.

Figure 36-1 shows a configuration where each Catalyst 4500 series switch acts as multiple virtual CEs. Because VRF-lite is a Layer 3 feature, each interface in a VRF must be a Layer 3 interface.

Figure 36-1 Catalyst 4500 Series Switches Acting as Multiple Virtual CEs

Figure 36-1 illustrates the packet-forwarding process in a VRF-lite CE-enabled network.

• When the CE receives a packet from a VPN, it looks up the routing table based on the input interface. When a route is found, the CE forwards the packet to the PE.
• When the ingress PE receives a packet from the CE, it performs a VRF lookup. When a route is found, the router adds a corresponding MPLS label to the packet and sends it to the MPLS network.
• When an egress PE receives a packet from the network, it strips the label and uses the label to identify the correct VPN routing table. The egress PE then performs the normal route lookup. When a route is found, it forwards the packet to the correct adjacency.
• When a CE receives a packet from an egress PE, it uses the input interface to look up the correct VPN routing table. If a route is found, the CE forwards the packet within the VPN.

To configure VRF, create a VRF table and specify the Layer 3 interface associated with the VRF. You then configure the routing protocols in the VPN and between the CE and the PE. BGP is the preferred routing protocol used to distribute VPN routing information across the providers’ backbone. The VRF-lite network has three major components:

• VPN route target communities—Lists all other members of a VPN community. You need to configure VPN route targets for each VPN community member.
• Multiprotocol BGP peering of VPN community PE routers—Propagates VRF reachability information to all members of a VPN community. You need to configure BGP peering in all PE routers within a VPN community.
• VPN forwarding—Transports all traffic between all VPN community members across a VPN service-provider network.

Default VRF-lite Configuration

Table 36-1 shows the default VRF configuration.

VRF-lite Configuration Guidelines

Consider these points when configuring VRF in your network:

• A switch with VRF-lite is shared by multiple customers, and all customers have their own routing tables.
• Because customers use different VRF tables, you can reuse the same IP addresses. Overlapped IP addresses are allowed in different VPNs.
• VRF-lite lets multiple customers share the same physical link between the PE and the CE. Trunk ports with multiple VLANs separate packets among customers. All customers have their own VLANs.
• VRF-lite does not support all MPLS-VRF functionality: label exchange, LDP adjacency, or labeled packets.
• For the PE router, there is no difference between using VRF-lite or using multiple CEs. In Figure 36-1, multiple virtual Layer 3 interfaces are connected to the VRF-lite device.
• The Catalyst 4500 series switch supports configuring VRF by using physical ports, VLAN SVIs, or a combination of both. You can connect SVIs through an access port or a trunk port.
• A customer can use multiple VLANs as long because they do not overlap with those of other customers. A customer’s VLANs are mapped to a specific routing table ID that is used to identify the appropriate routing tables stored on the switch.
• The Layer 3 TCAM resource is shared between all VRFs. To ensure that any one VRF has sufficient CAM space, use the maximum routes command.
• A Catalyst 4500 series switch using VRF can support one global network and up to 64 VRFs. The total number of routes supported is limited by the size of the TCAM.
• You can use most routing protocols (BGP, OSPF, EIGRP, RIP and static routing) between the CE and the PE. However, we recommend using external BGP (EBGP) for these reasons:

– BGP does not require multiple algorithms to communicate with multiple CEs.

– BGP is designed for passing routing information between systems run by different administrations.

– BGP makes it easy to pass attributes of the routes to the CE.

• VRF-lite does not support IGRP and ISIS.
• VRF-lite does not affect the packet switching rate.
• Multicast and VRF can be configured together on a Layer 3 interface.
• The Catalyst 4500 series switch supports all the PIM protocols (PIM-SM, PIM-DM, PIM-SSM, PIM BiDIR).
• The capability vrf-lite subcommand under router ospf should be used when configuring OSPF as the routing protocol between the PE and the CE.

Configuring VRFs

To configure one or more VRFs, perform this task:

Note For complete syntax and usage information for the following commands, see the switch command reference for this release and see the Cisco IOS Switching Services Command Reference at: http://www.cisco.com/en/US/docs/ios/ipswitch/command/reference/isw_book.html

Use the no ip vrf vrf-name global configuration command to delete a VRF and to remove all interfaces from it. Use the no ip vrf forwarding interface configuration command to remove an interface from the VRF.

Configuring VRF-Aware Services

IP services can be configured on global interfaces and within the global routing instance. IP services are enhanced to run on multiple routing instances; they are VRF-aware. Any configured VRF in the system can be specified for a VRF-aware service.

VRF-aware services are implemented in platform-independent modules. VRF provides multiple routing instances in Cisco IOS. Each platform has its own limit on the number of VRFs it supports.

VRF-aware services have the following characteristics:

• The user can ping a host in a user-specified VRF.
• ARP entries are learned in separate VRFs. The user can display Address Resolution Protocol (ARP) entries for specific VRFs.

These services are VRF-aware:

• ARP
• Ping
• Simple Network Management Protocol (SNMP)
• Unicast Reverse Path Forwarding (uRPF)
• Syslog
• Traceroute
• FTP and TFTP
• Telnet and SSH
• NTP

Configuring Per-VRF for TACACS+ Servers

The per-VRF for TACACS+ servers feature allows you to configure per-virtual route forwarding (per-VRF) authentication, authorization, and accounting (AAA) on TACACS+ servers.

Before configuring per-VRF on a TACACS+ server, you must have configured AAA and a server group. You can create the VRF routing table (shown in Steps 3 and 4) and configure the interface (Steps 6, 7, and 8). The actual configuration of per-VRF on a TACACS+ server is done in Steps 10 through 13.

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The following example lists all the steps to configure per-VRF TACACS+:

Switch> enable

Switch# configure terminal

Switch (config)# ip vrf cisco

Switch (config-vrf)# rd 100:1

Switch (config-vrf)# exit

Switch (config)# interface Loopback0

Switch (config-if)# ip vrf forwarding cisco

Switch (config-if)# ip address 10.0.0.2 255.0.0.0

Switch (config-if)# exit

Switch (config-sg-tacacs+)# ip vrf forwarding cisco

Switch (config-sg-tacacs+)# ip tacacs source-interface Loopback0

Switch (config-sg-tacacs)# exit

For more information about configuring per-VRF for TACACS+ server, see the
Cisco IOS Per VRF for TACACS + Server, Release 12.3(7)T.

Configuring Multicast VRFs

To configure multicast within a VRF table, perform this task:

For more information about configuring a multicast within a Multi-VRF CE, see the
Cisco IOS IP Multicast Configuration Guide, Release 12.4.

Use the no ip vrf vrf-name global configuration command to delete a VRF and to remove all interfaces from it. Use the no ip vrf forwarding interface configuration command to remove an interface from the VRF.

Configuring a VPN Routing Session

Routing within the VPN can be configured with any supported routing protocol (RIP, OSPF, or BGP) or with static routing. The configuration shown here is for OSPF, but the process is the same for other protocols.

To configure OSPF in the VPN, perform this task:

Use the no router ospf process-id vrf vrf-name global configuration command to disassociate the VPN forwarding table from the OSPF routing process.

The following examples configure a single VRF named VRF-RED:

Configuring BGP PE to CE Routing Sessions

To configure a BGP PE to CE routing session, perform this task:

Use the no router bgp autonomous-system-number global configuration command to delete the BGP routing process. Use the command with keywords to delete routing characteristics.

VRF-lite Configuration Example

Figure 36-2 is a simplified example of the physical connections in a network similar to that in Figure 36-1. OSPF is the protocol used in VPN1, VPN2, and the global network. BGP is used in the CE to PE connections. The example commands show how to configure the CE switch S8 and include the VRF configuration for switches S20 and S11 and the PE router commands related to traffic with switch S8. Commands for configuring the other switches are not included but would be similar.

Figure 36-2 VRF-lite Configuration Example

Displaying VRF-lite Status

To display information about VRF-lite configuration and status, perform one of the following tasks:

This example shows how to display multicast route table information within a VRF instance:

Note For more information about the information in the displays, refer to the Cisco IOS Switching Services Command Reference at:

http://www.cisco.com/en/US/docs/ios/ipswitch/command/reference/isw_book.html