Riverstone Networks WICT1-12 - Manual (Page 343)

Riverstone Networks RS Switch Router User Guide Release 8.0 17-35
MPLS Configuration Configuring L3 Label Switched Paths
See "Dynamic L3 LSP Configuration Example" for details on how to configure a dynamic LSP on the RS.
Adaptive LSP
An LSP can be rerouted if the explicit path is reconfigured or unable to connect. When an LSP is rerouting, the existing
path is torn down even if the new optimized route is not yet set up for traffic. Also, transit LSRs can allocate the same
amounts of bandwidth to both the old and new paths for the same LSP; this can cause over-allocation of available
bandwidth on some links.
To counter these problems, you can configure an LSP or an explicit path to be
adaptive
. An adaptive LSP or explicit
path retains its resources and continues to carry traffic until the new LSP or path is established. An adaptive LSP or
explicit path is torn down only when the new route is successfully set up for traffic. Note that if you specify an LSP to
be adaptive, all primary and secondary paths of the LSP are adaptive; the primary and secondary paths share bandwidth
on common links. If you specify a primary or secondary path to be adaptive, only that path will be adaptive.
Bandwidth
You can use the
bps
parameter to specify the bandwidth, in bits, to be reserved with RSVP for this LSP. ( The default
bandwidth value is 0.) If you specify a bandwidth, transit routers will reserve outbound link capacity for the LSP. LSP
setup may fail if there is a failure in bandwidth reservation.
CoS Value
A class of service (CoS) value places traffic into a transmission priority queue. For packets entering an LSP, the ingress
LSR can place a specific CoS value into the MPLS header. This CoS value enables all packets that enter the LSP to
receive the same class of service, as all LSRs in the LSP will use the CoS set by the ingress LSR. The MPLS header
and the CoS value are removed at the egress LSR.
You can assign the CoS value to be set by the ingress LSR by specifying the
class-of-service
parameter when
configuring the LSP. If you do not specify this parameter, the CoS value placed in the MPLS header is the value that
corresponds to the internal priority queue used to buffer the packet on the ingress LSR.
Hop Limit
The hop limit is the maximum number of hops, including the ingress and egress routers, allowed in the LSP. A hop
limit of 2 includes only the ingress and egress routers. The default hop limit is 255, which you can change with the
hop-limit
parameter.
LSP Metric
Assigning a metric to LSPs forces traffic to prefer certain LSPs over other LSPs, to prefer LSPs over IGP paths, or to
load share among LSPs or among LSPs and IGP paths. For example, if there are two or more LSPs to the same egress
router, the LSP with the lowest metric value is the preferred path. If the metric value is the same for multiple LSPs to
the same egress router, the traffic load is shared among the LSPs.