u can monitor bgp/ sessions on Cisco routers using free NMS tools like LibreNMS, Zabbix, Prometheus with SNMP exporter, or Cacti with BGP plugins. The best option is LibreNMS because it automatically discovers BGP peers and tracks session uptime, prefix counts, and even the prefix addresses (X.X.X.X/24 format). and as i can remember u need to enable first SNMP on your Cisco router with #snmp-server public RO . The key SNMP MIBs for BGP are BGP4-MIB (for session state, peer AS, uptime) and CISCO-BGP4-MIB. LibreNMS will poll these MIBs and display the data in graphs and tables.
and For prefix monitoring, focus on the tables in the Cisco MIB. LibreNMS does this automatically, but if using another tool, you may need to manually configure those OIDs.
Let me know if u'd like me to dive deeper into commandline details and configs. hope it helps G
-Enes
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