Q: Users inside the corporate office navigate to `wiki.company.com` and hit the fast, private internal server IP `10.0.5.10`. Users working from a coffee shop navigate to `wiki.company.com` and hit the public AWS Load Balancer IP `203.0.113.1`. How is the same domain name returning two completely different IPs without conflict?
This is achieved via Split-Horizon DNS.
#Networking #Networking #L2 #VPC #DNS #Security
🎙️ Candidate Opening & Architectural Context
""Isolating network failures requires proving whether packets are dropped by route tables, security groups, or stateless NACLs. The interviewer is testing: Split-Horizon DNS (Split-brain DNS).. I structure my answer around systematic triage first, root cause analysis second, and permanent remediation third.""
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🛠️ Production Runbook & Step-by-Step Resolution
1️⃣
Initial Diagnostics & Root Cause Analysis
This is achieved via Split-Horizon DNS.
- Internal Zone: The corporate office routers hand out internal DNS servers (like Active Directory DNS or Route 53 Resolver) via DHCP. These servers hold an authoritative internal zone for
company.comand return10.0.5.10. - External Zone: The rest of the world queries public DNS resolvers, which traverse to the public authoritative nameservers for
company.com(e.g., Route 53 Public Hosted Zone), which returns the public ALB IP203.0.113.1.
2️⃣
Remediation & Permanent Safeguards
DNS servers are configured to return different answers based on the originating IP address of the requester.
💡 The Senior SRE Gold Nugget (Key Architectural Takeaway)
"Pro-Tip: Internal Zone: The corporate office routers hand out internal DNS servers (like Active Directory DNS or Route 53 Resolver) via DHC."
⚡ 60-Second Elevator Pitch Talking Points
- Internal Zone: The corporate office routers hand out internal DNS servers (like Active Directory ...
- External Zone: The rest of the world queries public DNS resolvers, which traverse to the public a...
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