Page 52 7750 SR OS Services Guide
Operation of Class-Based Forwarding over RSVP LSPs
The 7750 SR class-based forwarding feature applies to a set of LSPs that are part of the same SDP.
Each LSP must be configured as part of an SDP specifying the forwarding classes it will support.
A forwarding class can only be assigned to one LSP in a given SDP, meaning that only one LSP
within an SDP will support a given class of service. However, multiple classes of services can be
assigned to an LSP. Both RSVP and static LSPs are allowed. All subclasses will be assigned to the
same LSP as the parent forwarding class.
When a service packet is received at an ingress SAP, it is classified into one of the eight 7750 SR
forwarding classes. If the packet will leave the SR on an SDP that is configured for class-based
forwarding, the outgoing LSP will be selected based on the packet's forwarding class. Each SDP
has a default LSP. The default LSP is used to forward a received packet that was classified at the
ingress SAP into a forwarding class for which the SDP does not have an explicitly-configured LSP
association. It is also used to forward a received packet if the LSP supporting its forwarding class
is down. Note that the SDP goes down if the default LSP is down.
Class-based forwarding can be applied to all services supported by the 7750 SR. For VPLS
services, explicit FC-to-LSP mappings are used for known unicast packets. Multicast and
broadcast packets use the default LSP. There is a per-SDP user configuration that optionally
overrides this behavior to specify an LSP to be used for multicast/broadcast packets.
VLL service packets are forwarded based on their forwarding class only if shared queuing is
enabled on the ingress SAP. Shared queuing must be enabled on the VLL ingress SAP if class-
forwarding is enabled on the SDP the service is bound to. Otherwise, the VLL packets will be
forwarded to the LSP which is the result of hashing the VLL service ID. Since there are eight
entries in the ECMP table for an SDP, one LSP ID for each forwarding class, the resulting load
balancing of VLL service ID is weighted by the number of times an LSP appears on that table. For
instance, if there are eight LSPs, the result of the hashing will be similar to when class based
forwarding is disabled on the SDP. If there are fewer LSPs, then the LSPs which were mapped to
more than one forwarding class, including the default LSP, will have proportionally more VLL
services forwarding to them.
Note that only user packets are forwarded based on their forwarding class. OAM packets are
forwarded in the same way as an SDP with class-based forwarding disabled. In other words, LSP
ping and LSP trace messages are queued in the queue corresponding to the forwarding class
specified by the user and are forwarded over the LSP being tested. Service and SDP OAM packets,
such as, service ping, VCCV ping, and SDP ping, are queued in the queue corresponding to the
forwarding class specified by the user and forwarded over the first available LSP.
Class-based forwarding is not supported for protocol packets tunneled through a SDP. All packets
are forwarded over the default LSP.
Class-based forwarding is not supported on a spoke SDP used for termination on an IES or VPRN
service. All packets are forwarded over the default LSP.
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