Context Isolation; Default Context; Restrictions And Recommendations - Cisco CRS Configuration Manual

MPLS LDP Carrier Supporting Carrier for Multiple VRFs
Also, a user must not configure the same LDP interface under more than one VRF.

Context Isolation

Each active VRF under LDP points to a separate context under which LDP runs. This means that various
variables, database, tables, FSM are kept separate in their respective VRF contexts and do not interfere or
interact with each other. This allows the LDP to provide per-VRF isolation and support CSC with customers
with overlapping addresses or routing information.

Default Context

The default (global) context is enabled at the time of the LDP process startup and remains enabled always. It
is not possible to disable IPv4 for the default context. Also, it is required to explicitly enable IPv4 for non-default
context. Therefore you can effectively disable IPv4 for non-default context by not configuring it. This means
that, it is possible to enable or disable the non-default context under LDP, whereas the same is not possible
for a default context.

Restrictions and Recommendations

The following restrictions and recommendations apply to the MPLS LDP CSC feature:
• Only IPv4 address family is supported for a default or a non-default VRF.
• No T-LDP support in a VRF context.
• An address family under VRF and VRF interface must be configured for non-default VRFs.
• Following scenarios are not supported :
• LDP router-id must be configured per-VRF. If not configured for non-default VRF, LDP computes
router-id from available loopback interfaces under the VRF.
• It is recommended to configure a routable discovery transport address under a VRF IPv4 address-family
submode for deterministic transport endpoint and connection.
• When LDP CSC is configured and in use:
Cisco IOS XR MPLS Configuration Guide for the Cisco CRS Router, Release 5.1.x
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◦ Different VRFs between a given PE-CE device pair (VRFs configured on different links and
interfaces)
◦ LDP/BGP CSC co-existence on a given VRF between a given PE-CE device pair:
◦ Single link
◦ Parallel links: LDP CSC on one link and BGP CSC on the other
◦ BGP label allocation policy for VRF prefixes must be per-prefix
◦ Selective VRF Download (SVD) feature must be disabled
Implementing MPLS Label Distribution Protocol