Description

BGP_PREFIX_SID_ATTR_CONFLICT: BGP prefix sid index: 1887 conflicting for reason: SRGB not configured. 

Symptoms

BGP_PREFIX_SID_ATTR_CONFLICT: BGP prefix sid index: 1887 conflicting for reason: SRGB not configured.

Solution

Segment Routing uses Multiprotocol Label Switching (MPLS) labels to create a path to guide a packet in a network. Using segment routing, an MPLS label range is reserved with MPLS Forwarding Infrastructure (MFI). This label range is called Segment Routing Global Block (SRGB).

A prefix SID assigned to a prefix is an extension of SRGB. To support segment routing, Border Gateway Protocol (BGP) requires the ability to advertise a segment identifier (SID) for a BGP prefix. A BGP-Prefix-SID is the segment identifier of the BGP prefix segment in a segment routing with a BGP network. 

When BGP nodes communicate with neighbor nodes in a network, the BGP Update, message sent to neighbor nodes, includes the Prefix-SID Label in Labeled Unicast NLRI and a prefix SID index in a new attribute called Prefix-SID attribute. 

Each BGP node assigns a local label to the neighbors and advertises the local label as adjacency SID through BGP--link state updates. 

The log was due to the new JUNOS release of 21.4R3-S1.5 which introduced the new feature, BGP-LU BGP Prefix SID support. Before this feature, the BGP router received updates from eBGP peers with Prefix-SID attribute are ignored; while with the feature, the attribute is recognized, and check the local configuration, since there was no BGP prefix segment enabled, so the log was seen.

A conflict in the BGP prefix SID is encountered while one of below:

•SRGB is not configured.

•SID index is out of range.

•Same SID index is used for multiple prefixes.
 

For more details regarding the feature, you might refer to the user manual:

https://www.juniper.net/documentation/us/en/software/junos/bgp/topics/ref/statement/srgb-edit-protocols-bgp-source-packet-routing.html

 

To reiterate, it is due to SRBG not being configured.

You can add accept-prefix-sid under a specific eBGP group or do the traffic engineering accordingly.

[edit protocols bgp]

root@R1_re# show

group test-ebgp-r4 {

   type external;

   family inet {

       labeled-unicast;

   }

   peer-as 65400;

   local-as 65100;

   neighbor 10.0.0.3;

   accept-prefix-sid;

}

It should be configured under the eBGP session

Modification History

2024-09-09 : Article Created