Configuring Local Label Allocation Control; Configuring Downstream On Demand - Cisco NCS 5500 Series Configuration Manual

Implementing MPLS Label Distribution Protocol
Configuration Example : Label Acceptance Control (Inbound Filtering)
This example shows how to configure label acceptance control. In this example, an LSR is configured to
accept and retain label bindings from neighbors for prefixes defined in access list .
RP/0/RP0/CPU0:Router(config)#mpls ldp
RP/0/RP0/CPU0:Router(config-ldp)#address-family ipv4
RP/0/RP0/CPU0:Router(config-ldp-af)#label remote accept from 192.168.1.1:0 for acl_1
RP/0/RP0/CPU0:Router(config-ldp-af)#label remote accept from 192.168.2.2:0 for acl_2
RP/0/RP0/CPU0:Router(config-ldp-af)#commit

Configuring Local Label Allocation Control

LDP creates label bindings for all IGP prefixes and receives label bindings for all IGP prefixes from all its
peers. If an LSR receives label bindings from several peers for thousands of IGP prefixes, it consumes
significant memory and CPU. In some scenarios, most of the LDP label bindings may not useful for any
application and you may required to limit the allocation of local labels. This is accomplished using LDP local
label allocation control, where an access list can be used to limit allocation of local labels to a set of prefixes.
Limiting local label allocation provides several benefits, including reduced memory usage requirements, fewer
local forwarding updates, and fewer network and peer updates.
Configuration Example
This example shows how to configure local label allocation using an IP access list to specify a set of prefixes
that local labels can allocate and advertise.
RP/0/RP0/CPU0:Router(config)# mpls ldp
RP/0/RP0/CPU0:Router(config-ldp)# address-family ipv4
RP/0/RP0/CPU0:Router(config-ldp-af)# label local allocate for pfx_acl_1
RP/0/RP0/CPU0:Router(config-ldp-af)# commit

Configuring Downstream on Demand

By default, LDP uses downstream unsolicited mode in which label advertisements for all routes are received
from all LDP peers. The downstream on demand feature adds support for downstream-on-demand mode,
where the label is not advertised to a peer, unless the peer explicitly requests it. At the same time, since the
peer does not automatically advertise labels, the label request is sent whenever the next-hop points out to a
peer that no remote label has been assigned.
In downstream on demand configuration, an ACL is used to specify the set of peers for downstream on demand
mode. For down stream on demand to be enabled, it needs to be configured on both peers of the session. If
only one peer in the session has downstream-on-demand feature configured, then the session does not use
downstream-on-demand mode.
Configuration Example
This example shows how to configure LDP Downstream on Demand.
RP/0/RP0/CPU0:Router(config)# mpls ldp
RP/0/RP0/CPU0:Router(config-ldp)# session downstream-on-demand with ACL1
RP/0/RP0/CPU0:Router(config-ldp)# commit
MPLS Configuration Guide for Cisco NCS 5500 Series Routers, IOS XR Release 6.2.x
Configuring Local Label Allocation Control
7