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JUNOS 10.1 Network Interfaces Configuration Guide
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 interface.
For most CCC connections that connect interfaces, the interfaces must be of the
same type; that is, ATM to ATM, Frame Relay to Frame Relay, PPP to PPP, or Cisco
HDLC to Cisco HDLC.
ATM-to-Ethernet interworking cross-connect circuits connect logical interfaces
configured on an ATM2 and Gigabit Ethernet IQ2 and IQ2-E or 10-Gigabit Ethernet
IQ2 and IQ2-E physical interfaces.
For all TCC connections that connect interfaces, the interfaces can be of unlike types.
Mainly, TCC is used for Layer 2.5 virtual private networks (VPNs), but it can also be
used as a simple "unlike circuit" switch.
Switching cross-connects join logical interfaces to form what is essentially Layer 2
switching.
Figure 10 on page 230 illustrates a Layer 2 switching circuit cross-connect. In this
topology, Router A and Router C have Frame Relay connections to Router B, which
is a Juniper Networks router. CCC allows you to configure Router B to act as a Frame
Relay (Layer 2) switch. To do this, 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 10: Layer 2 Switching Circuit Cross-Connect
If the Router A–to–Router B and Router B–to–Router C circuits are 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 CCC, Ethernet VLAN, and ATM circuits. With CCC, only like interfaces
can be connected in a single cross-connect. With TCC, unlike interfaces can be
connected in a single cross-connect. In Layer 2 switching cross-connects, the
exchanges take place between point-to-point links.
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Circuit and Translational Cross-Connects Overview
LSP stitching (LSP-to-LSP)—Cross-connects between LSPs provide a way to "stitch"
together two label-switched paths, including paths that fall in two different traffic
engineering database (TED) areas.
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