Configuring Layer 2 Switching Cross-Connects Using CCC
Layer 2 switching cross-connects join logical interfaces to form what is essentially Layer 2 switching. The interfaces that you connect must be of the same type.
Figure 1 illustrates a Layer 2 switching cross-connect. In this topology, Router A and Router C have Frame Relay connections to Router B, which is a Juniper Networks router. Circuit cross-connect (CCC) allows you to configure Router B to act as a Frame Relay (Layer 2) switch.
To configure Router B to act as a Frame Relay switch, you configure a circuit from Router A to Router C that passes through Router B, effectively configuring Router B as a Frame Relay switch with respect to these routers. This configuration allows Router B to transparently switch packets (frames) between Router A and Router C without regard to the packets’ contents or the Layer 3 protocols. The only processing that Router B performs is to translate DLCI 600 to 750.
Figure 1: Layer 2 Switching Cross-Connect
If the Router A–to–Router B and Router B–to–Router C circuits were PPP, for example, the Link Control Protocol and Network Control Protocol exchanges occur between Router A and Router C. These messages are handled transparently by Router B, allowing Router A and Router C to use various PPP options (such as header or address compression and authentication) that Router B might not support. Similarly, Router A and Router C exchange keepalives, providing circuit-to-circuit connectivity status.
You can configure Layer 2 switching cross-connects on PPP, Cisco HDLC, Frame Relay, Ethernet, and ATM circuits. In a single cross-connect, only like interfaces can be connected.
To configure Layer 2 switching cross-connects, you must configure the following on the router that is acting as the switch (Router B in Figure 1):
Configuring the CCC Encapsulation for Layer 2 Switching Cross-Connects
To configure Layer 2 switching cross-connects, configure the CCC encapsulation on the router that is acting as the switch (Router B in Figure 1).
 | Note: You cannot configure families on CCC interfaces; that is, you cannot include the family statement at the [edit interfaces interface-name unit logical-unit-number] hierarchy level. |
For instructions for configuring the encapsulation for Layer 2 switching cross-connects, see the following sections:
- Configuring ATM Encapsulation for Layer 2 Switching Cross-Connects
- Configuring Ethernet Encapsulation for Layer 2 Switching Cross-Connects
- Configuring Ethernet VLAN Encapsulation for Layer 2 Switching Cross-Connects
- Configuring Aggregated Ethernet Encapsulation for Layer 2 Switching Cross-Connects
- Configuring Frame Relay Encapsulation for Layer 2 Switching Cross-Connects
- Configuring PPP and Cisco HDLC Encapsulation for Layer 2 Switching Cross-Connects
Configuring ATM Encapsulation for Layer 2 Switching Cross-Connects
For ATM circuits, specify the encapsulation when configuring the virtual circuit (VC). Configure each VC as a circuit or a regular logical interface by including the following statements:
You can include these statements at the following hierarchy levels:
- [edit interfaces]
- [edit logical-systems logical-system-name interfaces]
Configuring Ethernet Encapsulation for Layer 2 Switching Cross-Connects
For Ethernet circuits, specify ethernet-ccc in the encapsulation statement. This statement configures the entire physical device. For these circuits to work, you must also configure a logical interface (unit 0).
Ethernet interfaces with standard Tag Protocol Identifier (TPID) tagging can use Ethernet CCC encapsulation. On M Series Multiservice Edge Routers, except the M320, one-port Gigabit Ethernet, two-port Gigabit Ethernet, four-port Gigabit Ethernet, and four-port Fast Ethernet PICs can use Ethernet CCC encapsulation. On T Series Core Routers and M320 routers, one-port Gigabit Ethernet and two-port Gigabit Ethernet PICs installed in FPC2 can use Ethernet CCC encapsulation. When you use this encapsulation type, you can configure the ccc family only.
You can include these statements at the following hierarchy levels:
- [edit interfaces]
- [edit logical-systems logical-system-name interfaces]
Configuring Ethernet VLAN Encapsulation for Layer 2 Switching Cross-Connects
An Ethernet virtual LAN (VLAN) circuit can be configured using either the vlan-ccc or extended-vlan-ccc encapsulation. If you configure the extended-vlan-ccc encapsulation on the physical interface, you cannot configure the inet family on the logical interfaces. Only the ccc family is allowed. If you configure the vlan-ccc encapsulation on the physical interface, both the inet and ccc families are supported on the logical interfaces. Ethernet interfaces in VLAN mode can have multiple logical interfaces.
For encapsulation type vlan-ccc, VLAN IDs from 512 through 4094 are reserved for CCC VLANs. For the extended-vlan-ccc encapsulation type, all VLAN IDs 1 and higher are valid. VLAN ID 0 is reserved for tagging the priority of frames.
| Note: Some vendors use the proprietary TPIDs 0x9100 and 0x9901 to encapsulate a VLAN-tagged packet into a VLAN-CCC tunnel to interconnect a geographically separated metro Ethernet network. By configuring the extended-vlan-ccc encapsulation type, a Juniper Networks router can accept all three TPIDs (0x8100, 0x9100, and 0x9901). |
Configure an Ethernet VLAN circuit with the vlan-ccc encapsulation as follows:
You can configure these statements at the following hierarchy levels:
- [edit interfaces]
- [edit logical-systems logical-system-name interfaces]
Configure an Ethernet VLAN circuit with the extended-vlan-ccc encapsulation statement as follows:
You can configure these statements at the following hierarchy levels:
- [edit interfaces]
- [edit logical-systems logical-system-name interfaces]
Whether you configure the encapsulation as vlan-ccc or extended-vlan-ccc, you must enable VLAN tagging by including the vlan-tagging statement.
Configuring Aggregated Ethernet Encapsulation for Layer 2 Switching Cross-Connects
You can configure aggregated Ethernet interfaces for CCC connections and for Layer 2 virtual private networks (VPNs).
Aggregated Ethernet interfaces configured with VLAN tagging can be configured with multiple logical interfaces. The only encapsulation available for aggregated Ethernet logical interfaces is vlan-ccc. When you configure the vlan-id statement, you are limited to VLAN IDs 512 through 4094.
Aggregated Ethernet interfaces configured without VLAN tagging can be configured only with the ethernet-ccc encapsulation. All untagged Ethernet packets received are forwarded based on the CCC parameters.
To configure aggregated Ethernet interfaces for CCC connections, include the ae0 statement at the [edit interfaces] hierarchy level:
Be aware of the following limitations when configuring CCC connections over aggregated Ethernet interfaces:
- If you configured load balancing between child links, be aware that a different hash key is used to distribute packets among the child links. Standard aggregated interfaces have family inet configured. An IP version 4 (IPv4) hash key (based on the Layer 3 information) is used to distribute packets among the child links. A CCC connection over an aggregated Ethernet interface has family ccc configured instead. Instead of an IPv4 hash key, an MPLS hash key (based on the destination media access control [MAC] address) is used to distributed packets among the child links.
- The extended-vlan-ccc encapsulation is not supported on the 12-port Fast Ethernet PIC and the 48-port Fast Ethernet PIC.
- The Junos OS does not support the Link Aggregation Control Protocol (LACP) when an aggregated interface is configured as a VLAN (with vlan-ccc encapsulation). LACP can be configured only when the aggregated interface is configured with the ethernet-ccc encapsulation.
For more information about how to configure aggregated Ethernet interfaces, see the Junos® OS Network Interfaces.
Configuring Frame Relay Encapsulation for Layer 2 Switching Cross-Connects
For Frame Relay circuits, specify the encapsulation when configuring the DLCI. Configure each DLCI as a circuit or a regular logical interface. The DLCI for regular interfaces must be from 1 through 511. For CCC interfaces, it must be from 512 through 4094.
You can configure these statements at the following hierarchy levels:
- [edit interfaces]
- [edit logical-systems logical-system-name interfaces]
Configuring PPP and Cisco HDLC Encapsulation for Layer 2 Switching Cross-Connects
For PPP and Cisco HDLC circuits, specify the encapsulation in the encapsulation statement. This statement configures the entire physical device. For these circuits to work, you must configure a logical interface (unit 0).
You can configure these statements at the following hierarchy levels:
- [edit interfaces type-fpc/pic/port]
- [edit logical-systems logical-system-name interfaces type-fpc/pic/port]
Configuring the CCC Connection for Layer 2 Switching Cross-Connects
To configure Layer 2 switching cross-connects, define the connection between the two circuits by including the interface-switch statement. You configure this connection on the router that is acting as the switch (Router B in Figure 1). The connection joins the interface that comes from the circuit’s source to the interface that leads to the circuit’s destination. When you specify the interface names, include the logical portion of the name, which corresponds to the logical unit number. The cross-connect is bidirectional, so packets received on the first interface are transmitted out the second interface, and those received on the second interface are transmitted out the first.
You can include this statement at the following hierarchy levels:
- [edit protocols connections]
- [edit logical-systems logical-system-name protocols connections]
Configuring MPLS for Layer 2 Switching Cross-Connects
For Layer 2 switching cross-connects to work, you must enable MPLS on the router by including at least the following statements. This minimum configuration enables MPLS on a logical interface for the switching cross-connect.
Include the family mpls statement:
You can configure this statement at the following hierarchy levels:
- [edit interfaces interface-name unit logical-unit-number]
- [edit logical-systems logical-system-name interfaces interface-name unit logical-unit-number]
You can then specify this logical interface in the MPLS protocol configuration:
You can configure these statements at the following hierarchy levels:
- [edit protocols]
- [edit logical-systems logical-system-name protocols]
Example: Configuring a Layer 2 Switching Cross-Connect
Configure a full-duplex Layer 2 switching cross-connect between Router A and Router C, using a Juniper Networks router, Router B, as the virtual switch. See the topology in Figure 2 and Figure 3.
Figure 2: Topology of a Frame Relay Layer 2 Switching Cross-Connect
Figure 3: Sample Topology of a VLAN Layer 2 Switching Cross-Connect
