“Before modern Cloudflare Anycast DNS existed, steering global user traffic across multiple physical data centers required Cisco GSS DNS delegation and Cisco CSS HTTP probes.”

While expanding Net4 India’s cloud hosting infrastructure across Delhi and Chennai datacenters in 2012, client applications required active-active global load balancing.

Architecture: Multi-Region GSLB with Cisco CSS & GSS

We deployed a 2-tier load balancing architecture using Cisco GSS 4400 (Global Site Selector) and Cisco CSS 11500 (Content Services Switch).

1. DNS Delegation (GSS 4400): Authoritative DNS queries for app.net4.in were delegated to Cisco GSS appliances.
2. Health Probe Monitoring: GSS polled local Cisco CSS load balancers in Delhi and Chennai via KALAP (Keep-Alive Application Protocol) and HTTP probes.
3. Dynamic DNS Response: If Delhi’s ISP uplinks experienced degradation, GSS automatically altered DNS A-record responses to steer incoming users to Chennai VIPs.

[!TIP] Keep DNS TTLs low (30 seconds) on GSLB delegated records to force client browsers to re-query DNS during regional failovers.

# # Cisco GSS 4400 CLI Configuration Snippet
gss-config
  answer-alias APP-GSLB
    answer-type a-record
    add-answer 192.168.10.100  # Delhi VIP
    add-answer 192.168.20.100  # Chennai VIP
  dns-clause APP-RULE
    match-domain app.net4.in
    enable-answer APP-GSLB
    balance-method least-loaded

The Verdict

Key Takeaway

Leverage Health-Aware DNS Delegation for Multi-Region Application High Availability.

Deploying Cisco GSS & CSS GSLB proved that dynamic DNS steering based on real-time application health probes prevents regional datacenter outages from impacting end users.