Certain applications in the SR OS require extra traffic processing in the forwarding plane. Such additional traffic processing is facilitated by an internal cross-connect that uses PXC ports (described in the Port Cross-Connect). Application-specific use of the cross-connect is built on the common premise that the traffic must be steered from the input ports to the PXC ports where the traffic can be looped for additional processing in the forwarding plane. To shield the operator from the intricacies involved when configuring application-specific cross-connect attributes, a CLI construct referred to as Forwarding Path Extensions (FPE) simplifies provisioning of various applications which rely on PXC functionality. Two examples of applications which rely on PXC and FPE are:
Anchored PW-ports where PW payload termination in Layer 3 services is disjointed from I/O ports in the system.
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VXLAN termination on non-system IPv4 addresses and VXLAN IPv6 underlay.
Application-specific uses of PXC ports and FPEs are described in the respective user guides (7450 ESS, 7750 SR, and VSR Triple Play Service Delivery Architecture Guide, 7450 ESS, 7750 SR, 7950 XRS, and VSR Layer 3 Services Guide: IES and VPRN, and 7450 ESS, 7750 SR, 7950 XRS, and VSR Layer 2 Services and EVPN Guide: VLL, VPLS, PBB, and EVPN).
The FPE configuration provides information to the SR OS node necessary to associate the application with the PXC (paired PXC sub-ports or PXC based LAG ids). Consequently, the SR OS node sets up the internal logic utilizing PXC as required by the application.
An example of FPE provisioning is given in Figure 1.
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The first three steps are applicable to PXC port provisioning.
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Association between the application and the PXC is performed in steps 4 and 5. In this particular example, two applications can be configured: PW-port or VXLAN-termination (non-system IPv4 termination or IPv6 underlay). These applications require internal configuration of SDPs and their IDs are allocated from the user configurable range. To prevent conflict between the user provisioned SDP IDs and internally configured SDP ID in FPE case, a range of SDP IDs that are used by FPE is reserved by the sdp-id-range commands under the config>fwd-path-ext CLI hierarchy.
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Application-specific configuration is performed in step 6, partially by the operator and partially by the system. This is described in the application- specific user guides.
After the PXC sub-port or LAG is associated with an FPE object, the manual creation (by the operator) of IP interfaces and SAPs under such PXC sub-ports/LAGs is not permitted. Only the internal SR OS system is allowed to reference these PXC sub-ports/LAGs in internal IP interfaces and SAPs, as required by each application.
However, the PXC sub-ports and LAG parameters (QoS, lag-profiles, and so on) can be modified by the operator.
PXC sub-ports or LAGs can be removed from the FPE object only if they are not associated with an application.