BGP routes in certain IP ranges (e.g., 172.x.x.x) were not being advertised from a Juniper SSR router due to an incorrectly configured prefix filter. The issue was traced to a prefix range of 0.0.0.0/1–32, which inadvertently excluded part of the IPv4 address space. Updating the filter to 0.0.0.0/0–32 resolved the issue.

Only certain prefixes (e.g., 10.x.x.x) were being advertised to BGP peers.

Other valid routes (e.g., 172.x.x.x) were missing from show bgp vrf <VRF> <prefix> output, showing:

Not advertised to any peer

Route filtering policy applied:

Block_Default_To_Core-out-non-overlay-VRF_<VRF>

show bgp neighbors <peer> advertised-routes showed incomplete prefix list.

Root Cause:

The outbound routing policy referenced a prefix filter defined as:

prefix-filter Block_Default_To_Core-s1-prefix-filter
  rule r0 prefix 0.0.0.0/1
  rule r0 le     32

This configuration only matched prefixes in the range 0.0.0.0 – 127.255.255.255, excluding all prefixes with higher-order bits starting with 1 (i.e., 128.0.0.0/1–255.255.255.255).

As a result, prefixes like 172.x.x.x were filtered out and never advertised.

To fix the issue, update the prefix filter to correctly include the entire IPv4 address space and explicitly block only the default route.

prefix-filter Block_Default_To_Core-s1-prefix-filter

 rule r0 prefix 0.0.0.0/0

 rule r0 policy reject

 rule r1 prefix 0.0.0.0/0

 rule r1 le 32

 rule r1 policy accept

or equivalently (if policy context allows):

0.0.0.0/0 Reject

0.0.0.0/0-32 Accept

Default route (0.0.0.0/0) remains blocked.

All other IPv4 prefixes (0.0.0.0/1–255.255.255.255) are now advertised successfully.