Pbts Restrictions - Cisco ASR 9000 Series Configuration Manual

Policy-Based Tunnel Selection

PBTS Restrictions

When implementing PBTS, the following restrictions are listed:
• When QoS EXP remarking on an interface is enabled, the EXP value is used to determine the egress
tunnel interface, not the incoming EXP value.
• Egress-side remarking does not affect PBTS tunnel selection.
• PBTS does not support selecting a TE tunnel for the route driven from Access Based Forwarding (ABF)
lookup result.
• PBTS does not support generic routing encapsulation over traffic engineering (GREoTE).
• PBTS is supported only on L3 interfaces.
• PBTS tunnel selection is not supported on the tunnels with L2VPN configuration.
• PBTS does not support VidMon feature.
• PBTS does not support slow path, instead, default forward class is used.
• PBTS does not support subscriber sessions.
• Forward-class configuration does not apply to the FRR backup tunnels and will be ignored.
• Note that forward-class configuration will not be supported for the auto-backup tunnels.
• Forward-class configuration is not supported for P2MP-TE (MTE) tunnels.
• The policy-class configuration does not co-exist with forward-class configuration.
• DSCP, precedence, or ToS based classification has to be configured through ACL.
• PBTS supports multi-pass implementation only for IPv4 packets.
PBTS Default Class Enhancement
Policy Based Tunnel Selection (PBTS) provides a mechanism that directs traffic into TE tunnels based on
incoming packets TOS/EXP bits. The PBTS default class enhancement can be explained as follows:
• Add a new class called default so that you can configure a tunnel of class (1-7 or default). You can
configure more than one default tunnels. By default, tunnels of class 0 no longer serves as default tunnel.
• The control plane can pick up to 8 default tunnels to carry default traffic.
• The forwarding plane applies the same load-balancing logic on the default tunnels such that default
traffic load is shared over them.
• Default tunnels are not used to forward traffic if each class of traffic is served by at least one tunnel of
the respective class.
• A tunnel is implicitly assigned to class 0 if the tunnel is not configured with a specific class.
• If no default tunnel is available for forwarding, the lowest class tunnels are assigned to carry default
traffic only.
• Both LDP and IGP paths are assigned to a new default class. LDP and IGP no longer statically associate
to class 0 in the platforms, which support this new default class enhancement.
Cisco ASR 9000 Series Aggregation Services Router MPLS Configuration Guide, Release 4.3.x
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Implementing MPLS Traffic Engineering
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