What is the purpose of max-prefix limits on BGP sessions and how should you set them?

• A. Limit the number of IPv6 prefixes
• B. Protect routers from memory exhaustion during route floods; set to reasonable multiple of expected routes
• C. Limit the number of peers
• D. Prevent any updates from being accepted

Answer: (B)

Max-prefix limits act as a safety guardrail for BGP sessions. They cap how many prefixes a neighbor can advertise to you, protecting the router from memory exhaustion and high CPU load if a peer floods the session with routes, whether due to churn, misconfiguration, or a sudden surge. When the configured limit is reached, the router typically stops accepting more prefixes from that neighbor or resets the session, which is a controlled reaction that prevents resource exhaustion and instability across the routing table. The best practice is to set the limit to a reasonable multiple of what you expect from that neighbor under normal operation, with some headroom for growth and temporary spikes. Apply this per session and per address family (IPv4 and IPv6) based on actual traffic and hardware capacity. The other options aren’t appropriate because the feature isn’t about limiting the number of peers, nor is it limited to IPv6 prefixes only, nor is it about blocking all updates entirely; it’s about preventing unbounded growth of accepted routes.