BGP Labeled Unicast with Implicit Null Label for Local Routes

Overview

In OcNOS, by default, the BGP router allocates a unique, valid MPLS label (>16) for all the IPv4 routes when allocate-label (all | route-map NAME) command is issued. The BGP Labeled Unicast (BGP LU) attaches the MPLS label to the routes and advertises them to its peers. This existing functionality is enhanced for Penultimate hop popping (PHP) requirement with an implicit null label allocation only for locally originated IPv4 routes, whether connected or redistributed from other protocols. Meanwhile, the non local routes are assigned with a valid MPLS label. Using PHP with implicit null eliminates the unnecessary label allocation, providing a more efficient and effective solution for handling local routes in the BGP-LU. If BGP LU is deployed in multiple segments, the implicit null label plays a significant role in the last segment.

A new CLI is introduced under the BGP router configuration mode. When the CLI is configured, the BGP implicit null label allocation is applied only after the expiry of the currently active BGP RIB scan timer that validates all the routes at the configured interval time.

This feature is supported on Qumran1 (Q1) series platforms, Qumran2 (Q2) series platforms, and Qumran (Q1 and Q2) series platforms (Q1, Q2 Qax Qux Q2c, Qmx).

Benefits

The regular MPLS label allocation for connected routes necessitates additional label processing on the egress Provider Edge (PE) and, sometimes, fails to forward traffic. The BGP LU with IMPLICIT NULL support reduces the label processing overheads at the egress node and efficiently uses the hardware FEC resources during route allocation.

Prerequisites

The following is mandatory before issuing the bgp implicit-null CLI:

• Set up the global BGP configuration using the command allocate-label (all | route-map NAME) to assign MPLS labels for IPv4 unicast routes. This configuration ensures that IPv4 unicast routes are qualified for MPLS label assignment. The following show running sample output illustrates that the MPLS labels are assigned to the routes.

Copy

!
router bgp 100
 allocate-label all
 neighbor 11.11.11.55 remote-as 100
 neighbor 172.3.4.53 remote-as 100
 neighbor 11.11.11.55 update-source lo
 !
 address-family ipv4 unicast
 network 21.21.21.56/32
 exit-address-family
 !

•

Configuring BGP implicit null among network peers running different OcNOS versions earlier than 6.5.x causes traffic drops. To restore traffic flow, remove the implicit null configuration. Additionally, to implement this feature, ensure all peers are using version 6.5.x or higher.

Topology

In this topology, PE1 node advertise all connected or local IPv4 unicast routes advertised in labeled-unicast address-family mode with implicit null label to remote PE2 via ABR node.

Figure 80. BGP labeled unicast with Implicit Null Label