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Configuring IP Router Parameters
QPPB When Next-Hops are Resolved by QPPB Routes
In some circumstances (IP VPN inter-AS model C, Carrier Supporting Carrier, indirect static
routes, etc.) an IPv4 or IPv6 packet may arrive on a QPPB-enabled interface and match a route A1
whose next-hop N1 is resolved by a route A2 with next-hop N2 and perhaps N2 is resolved by a
route A3 with next-hop N3, etc. In release 9.0 the QPPB result is based only on the forwarding-
class and priority of route A1. If A1 does not have a forwarding-class and priority association then
the QoS classification is not based on QPPB, even if routes A2, A3, etc. have forwarding-class and
priority associations.
QPPB and Multiple Paths to a Destination
When ECMP is enabled some routes may have multiple equal-cost next-hops in the forwarding
table. When an IP packet matches such a route the next-hop selection is typically based on a hash
algorithm that tries to load balance traffic across all the next-hops while keeping all packets of a
given flow on the same path. The QPPB configuration model described in
Priority with a Route on page 28
different ECMP next-hops of a route. The forwarding-class and priority of a packet matching an
ECMP route is based on the particular next-hop used to forward the packet.
When Edge PIC [1] is enabled some BGP routes may have a backup next-hop in the forwarding
table in addition to the one or more primary next-hops representing the equal-cost best paths
allowed by the ECMP/multipath configuration. When an IP packet matches such a route a
reachable primary next-hop is selected (based on the hash result) but if all the primary next-hops
are unreachable then the backup next-hop is used. The QPPB configuration model described in
Associating an FC and Priority with a Route on page 28
associated with the backup path to be different from the QoS characteristics of the equal-cost best
paths. The forwarding class and priority of a packet forwarded on the backup path is based on the
fc and priority of the backup route.
QPPB and Policy-Based Routing
When an IPv4 or IPv6 packet with destination address X arrives on an interface with both QPPB
and policy-based-routing enabled:
•
•
Page 32
There is no QPPB classification if the IP filter action redirects the packet to a directly
connected interface, even if X is matched by a route with a forwarding-class and priority
QPPB classification is based on the forwarding-class and priority of the route matching IP
address Y if the IP filter action redirects the packet to the indirect next-hop IP address Y,
even if X is matched by a route with a forwarding-class and priority
allows different QoS information to be associated with the
7450 ESS OS Router Configuration Guide
Associating an FC and
allows the forwarding-class and priority
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