- About this Manual
- Chapter 1, Overview
- Chapter 2, CTC Operations
- Chapter 3, Initial Configuration
- Chapter 4, Configuring Interfaces
- Chapter 5, Configuring Bridging
- Chapter 6, Configuring STP and RSTP
- Chapter 7, Configuring VLANs
- Chapter 8, Configuring 802.1Q and Layer 2 Protocol Tunneling
- Chapter 9, Configuring Link Aggregation
- Chapter 10, Configuring Networking Protocols
- Chapter 11, Configuring IRB
- Chapter 12, Configuring VRF Lite
- Chapter 13, Configuring Quality of Service
- Chapter 14, Configuring the Switching Database Manager
- Chapter 15, Configuring Access Control Lists
- Appendix A, Command Reference
- Appendix B Cisco IOS Commands Not Supported in ML-Series Card Software
- Appendix C, Using Technical Support
Configuring IEEE 802.1Q and Layer 2 Protocol Tunneling
Virtual private networks (VPNs) provide enterprise-scale connectivity on a shared infrastructure, often Ethernet-based, with the same security, prioritization, reliability, and manageability requirements of private networks. Tunneling is a feature designed for service providers who carry traffic of multiple customers across their networks and are required to maintain the VLAN and Layer 2 protocol configurations of each customer without impacting the traffic of other customers. The ML-Series cards support IEEE 802.1Q tunneling and Layer 2 protocol tunneling.
This chapter contains these sections:
•
Understanding IEEE 802.1Q Tunneling
•Configuring IEEE 802.1Q Tunneling
•Understanding Layer 2 Protocol Tunneling
•Configuring Layer 2 Protocol Tunneling
•Monitoring and Verifying Tunneling Status
Understanding IEEE 802.1Q Tunneling
Business customers of service providers often have specific requirements for VLAN IDs and the number of VLANs to be supported. The VLAN ranges required by different customers in the same service-provider network might overlap, and traffic of customers through the infrastructure might be mixed. Assigning a unique range of VLAN IDs to each customer would restrict customer configurations and could easily exceed the VLAN limit of 4096 of the IEEE 802.1Q specification.
Using the IEEE 802.1Q tunneling feature, service providers can use a single VLAN to support customers who have multiple VLANs. Customer VLAN IDs are preserved and traffic from different customers is segregated within the service-provider infrastructure even when they appear to be on the same VLAN. The IEEE 802.1Q tunneling expands VLAN space by using a VLAN-in-VLAN hierarchy and tagging the tagged packets. A port configured to support IEEE 802.1Q tunneling is called a tunnel port. When you configure tunneling, you assign a tunnel port to a VLAN that is dedicated to tunneling. Each customer requires a separate VLAN, but that VLAN supports all of the customer's VLANs.
Customer traffic tagged in the normal way with appropriate VLAN IDs comes from an IEEE 802.1Q trunk port on the customer device and into a tunnel port on the ML-Series card. The link between the customer device and the ML-Series card is an asymmetric link because one end is configured as an IEEE 802.1Q trunk port and the other end is configured as a tunnel port. You assign the tunnel port interface to an access VLAN ID unique to each customer. See Figure 8-1.
Figure 8-1 IEEE 802.1Q Tunnel Ports in a Service-Provider Network
Packets coming from the customer trunk port into the tunnel port on the ML-Series card are normally IEEE 802.1Q-tagged with appropriate VLAN ID. The tagged packets remain intact inside the ML-Series card and, when they exit the trunk port into the service provider network, are encapsulated with another layer of an IEEE 802.1Q tag (called the metro tag) that contains the VLAN ID unique to the customer. The original IEEE 802.1Q tag from the customer is preserved in the encapsulated packet. Therefore, packets entering the service-provider infrastructure are double-tagged, with the outer tag containing the customer's access VLAN ID, and the inner VLAN ID being the VLAN of the incoming traffic.
When the double-tagged packet enters another trunk port in a service provider ML-Series card, the outer tag is stripped as the packet is processed inside the switch. When the packet exits another trunk port on the same core switch, the same metro tag is again added to the packet. Figure 8-2 shows the structure of the double-tagged packet.
Figure 8-2 Normal, IEEE 802.1Q, and 802.1Q Tunneled Ethernet Packet Formats
When the packet enters the trunk port of the service-provider egress switch, the outer tag is again stripped as the packet is processed internally on the switch. However, the metro tag is not added when it is sent out the tunnel port on the edge switch into the customer network, and the packet is sent as a normal IEEE 802.1Q-tagged frame to preserve the original VLAN numbers in the customer network.
In Figure 8-1, Customer A was assigned VLAN 30, and Customer B was assigned VLAN 40. Packets entering the ML-Series card tunnel ports with IEEE 802.1Q tags are double-tagged when they enter the service-provider network, with the outer tag containing VLAN ID 30 or 40, appropriately, and the inner tag containing the original VLAN number, for example, VLAN 100. Even if both Customers A and B have VLAN 100 in their networks, the traffic remains segregated within the service-provider network because the outer tag is different. With IEEE 802.1Q tunneling, each customer controls its own VLAN numbering space, which is independent of the VLAN numbering space used by other customers and the VLAN numbering space used by the service-provider network.
At the outbound tunnel port, the original VLAN numbers on the customer's network are recovered. If the traffic coming from a customer network is not tagged (native VLAN frames), these packets are bridged or routed as if they were normal packets, and the metro tag is added (as a single-level tag) when they exit toward the service provider network.
If using the native VLAN (VLAN 1) in the service provider network as a metro tag, it is important that this tag always be added to the customer traffic, even though the native VLAN ID is not normally added to transmitted frames. If the VLAN 1 metro tag were not added on frames entering the service provider network, then the customer VLAN tag would appear to be the metro tag, with disastrous results. The global configuration command "vlan dot1q tag native" must be used to prevent this by forcing a tag to be added to VLAN 1. Avoiding the use of VLAN 1 as a metro tag transporting customer traffic is recommended to reduce the risk of misconfiguration. A best practice is to use VLAN 1 as a private management VLAN in the service provider network.
The IEEE 802.1Q class of service (COS) priority field on the added metro tag is set to zero by default, but may be modified by input or output policy maps.
Configuring IEEE 802.1Q Tunneling
This section includes this information about configuring IEEE 802.1Q tunneling:
•IEEE 802.1Q Tunneling and Other Features
•Configuring an IEEE 802.1Q Tunneling Port
Note By default, IEEE 802.1Q tunneling is not configured on the ML-Series.
IEEE 802.1Q Tunneling and Other Features
Although IEEE 802.1Q tunneling works well for Layer 2 packet switching, there are incompatibilities with some Layer 2 features and with Layer 3 switching.
•A tunnel port cannot be a routed port.
•Tunnel ports do not support IP access control lists (ACLs).
•Layer 3 quality of service (QoS) ACLs and other QoS features related to Layer 3 information are not supported on tunnel ports. MAC-based QoS is supported on tunnel ports.
•EtherChannel port groups are compatible with tunnel ports as long as the IEEE 802.1Q configuration is consistent within an EtherChannel port group.
•Port Aggregation Protocol (PAgP) and Unidirectional Link Detection (UDLD) Protocol are not supported on IEEE 802.1Q tunnel ports.
•Dynamic Trunking Protocol (DTP) is not compatible with IEEE 802.1Q tunneling because you must manually configure asymmetric links with tunnel ports and trunk ports.
•Loopback detection is supported on IEEE 802.1Q tunnel ports.
•When a port is configured as an IEEE 802.1Q tunnel port, spanning tree bridge protocol data unit (BPDU) filtering is automatically disabled on the interface.
Configuring an IEEE 802.1Q Tunneling Port
Beginning in privileged EXEC mode, follow these steps to configure a port as an IEEE 802.1Q tunnel port:
Note The VLAN ID (VID) range of 2 to 4095 is recommended for IEEE 802.1Q tunneling on the ML-Series card.
Note If VID 1 is required, use the following command: Router (config)# VLAN dot1Q tag native
Use the no mode dot1q-tunnel interface configuration command to remove the IEEE 802.1Q tunnel from the interface.
The following sections show how to configure the example in Figure 8-1. The first section applies to Router_A, and the second section applies to Router_B.
Router A Configuration Example
bridge 30 protocol ieee
bridge 40 protocol ieee
interface FastEthernet0
no ip routing
no ip address
mode dot1q-tunnel
bridge-group 30
!
interface FastEthernet1
no ip address
mode dot1q-tunnel
bridge-group 40
!
interface POS0
no ip address
crc 32
pos flag c2 1
!
interface POS0.1
encapsulation dot1Q 30
bridge-group 30
!
interface POS0.2
encapsulation dot1Q 40
bridge-group 40
Router B Configuration Example
bridge 30 protocol ieee
bridge 40 protocol ieee
interface FastEthernet0
no ip routing
no ip address
mode dot1q-tunnel
bridge-group 30
!
interface FastEthernet1
no ip address
mode dot1q-tunnel
bridge-group 40
!
interface POS0
no ip address
crc 32
pos flag c2 1
!
interface POS0.1
encapsulation dot1Q 30
bridge-group 30
!
interface POS0.2
encapsulation dot1Q 40
bridge-group 40
Understanding Layer 2 Protocol Tunneling
Customers at different sites connected across a service-provider network need to run various Layer 2 protocols to scale their topology to include all remote sites, as well as the local sites. STP must run properly, and every VLAN should build a proper spanning tree that includes the local site and all remote sites across the service-provider infrastructure. Cisco Discovery Protocol (CDP) must discover neighboring Cisco devices from local and remote sites. VLAN Trunking Protocol (VTP) must provide consistent VLAN configuration throughout all sites in the customer network.
When protocol tunneling is enabled, edge switches on the inbound side of the service-provider infrastructure encapsulate Layer 2 protocol packets with a special MAC address and send them across the service-provider network. Core switches in the network do not process these packets, but forward them as normal packets. Layer 2 protocol data units (PDUs) for CDP, Spanning-Tree Protocol (STP), or Virtual terminal Protocol (VTP) cross the service-provider infrastructure and are delivered to customer switches on the outbound side of the service-provider network. Identical packets are received by all customer ports on the same VLANs with the following results:
•Users on each of a customer's sites are able to properly run STP and every VLAN can build a correct spanning tree based on parameters from all sites and not just from the local site.
•CDP discovers and shows information about the other Cisco devices connected through the service-provider network.
•VTP provides consistent VLAN configuration throughout the customer network, propagating through the service provider to all switches.
Layer 2 protocol tunneling can be used independently or to enhance IEEE 802.1Q tunneling. If protocol tunneling is not enabled on IEEE 802.1Q tunneling ports, remote switches at the receiving end of the service-provider network do not receive the PDUs and cannot properly run STP, CDP, and VTP. When protocol tunneling is enabled, Layer 2 protocols within each customer's network are totally separate from those running within the service-provider network. Customer switches on different sites that send traffic through the service-provider network with IEEE 802.1Q tunneling achieve complete knowledge of the customer's VLAN. If IEEE 802.1Q tunneling is not used, you can still enable Layer 2 protocol tunneling by connecting to the customer switch through access ports and enabling tunneling on the service-provider access port.
Configuring Layer 2 Protocol Tunneling
You enable Layer 2 protocol tunneling (by protocol) on the tunnel ports that are connected to the customer in the edge switches of the service-provider network. ML-Series card tunnel ports are connected to customer IEEE 802.1Q trunk ports. The ML-Series card supports Layer 2 protocol tunneling for CDP, STP, and VTP. The ML-Series cardes connected to the customer switch perform the tunneling process.
When the Layer 2 PDUs that entered the inbound ML-Series switch through the tunnel port exit the switch through the trunk port into the service-provider network, the switch overwrites the customer PDU-destination MAC address with a well-known Cisco proprietary multicast address (01-00-0c-cd-cd-d0). If IEEE 802.1Q tunneling is enabled, packets are also double-tagged; the outer tag is the customer metro tag and the inner tag is the customer VLAN tag. The core switches ignore the inner tags and forward the packet to all trunk ports in the same metro VLAN. The ML-Series switches on the outbound side restore the proper Layer 2 protocol and MAC address information and forward the packets. Therefore, the Layer 2 PDUs are kept intact and delivered across the service-provider infrastructure to the other side of the customer network.
This section contains this information about configuring Layer 2 protocol tunneling:
•Default Layer 2 Protocol Tunneling Configuration
•Layer 2 Protocol Tunneling Configuration Guidelines
•Monitoring and Verifying Tunneling Status
Default Layer 2 Protocol Tunneling Configuration
Table 8-1 shows the default Layer 2 protocol tunneling configuration.
Layer 2 Protocol Tunneling Configuration Guidelines
These are some configuration guidelines and operating characteristics of Layer 2 protocol tunneling:
•The switch supports tunneling of CDP, STP (including multiple STP [MSTP], and VTP protocols. Protocol tunneling is disabled by default but can be enabled for the individual protocols on IEEE 802.1Q tunnel ports.
•Tunneling is not supported on trunk ports. If you enter the l2protocol-tunnel interface configuration command on a trunk port, the command is accepted, but Layer 2 tunneling does not take affect unless you change the port to a tunnel port.
•EtherChannel port groups are compatible with tunnel ports as long as the IEEE 802.1Q configuration is consistent within an EtherChannel port group.
•If an encapsulated PDU (with the proprietary destination MAC address) is received from a tunnel port or access port with Layer 2 tunneling enabled, the tunnel port is shut down to prevent loops.
•Only decapsulated PDUs are forwarded to the customer network. The spanning tree instance running on the service-provider network does not forward BPDUs to tunnel ports. No CDP packets are forwarded from tunnel ports.
•Because tunneled PDUs (especially STP BPDUs) must be delivered to all remote sites for the customer virtual network to operate properly, you can give PDUs higher priority within the service-provider network than data packets received from the same tunnel port. By default, the PDUs use the same CoS value as data packets.
•Protocol tunneling has to be configured symmetrically at both the ingress and egress point. For example, if you configure the entry point to tunnel STP, CDP, VTP, then you must configure the egress point in the same way.
Configuring a Layer 2 Tunneling Port
Beginning in privileged EXEC mode, follow these steps to configure a port as a Layer 2 tunnel port:
Monitoring and Verifying Tunneling Status
Table 8-2 shows the privileged EXEC commands for monitoring and maintaining IEEE 802.1Q and Layer 2 protocol tunneling.
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