ARS Optimization Vrf Mode Big

Introduction

This feature is called Deterministic Large VRF Support, which allows for greater scale in the number of routes a vrf holds.

Mode Big

  • Introduced in 4.1.1 IOS-XR.
  • Support up to 16 vrf with extended vrf space.
  • After changing the mode as big, the corresponding VRF must be re-configured.
  • The default vrf instance can only have 64K routes, with mode big it is expended to 4M depending on the line card (4M Typhoon).
  • Feature should be enabled when installing the full internet routing table in a vrf.
  • Below is a potential error that can be received if the mode is not enabled:
LC/0/0/CPU0:Feb 19 16:42:55.833 : prm_server_tr[295]: %PLATFORM-NP-3-OOR : Routing Table Full : PRM failed to install a route 
(114.255.239.0/24) because the subtree  was full. Each subtree is limited to 262144 routes per subtree.
Subtree where install failed is 114.0.0.0/8

Relevant Commands

mode big

RP/0/RSP0/CPU0:router(config-vrf)# mode big

Additional Resources

Deterministic Large VRF Support - ASR Release notes.
ASR9K - PLATFORM-NP-3-OOR Error - c-nsp
Internet in a VRF and LFIB Explosion - IP Space Blog (Catalyst 6500).

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