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Validating DNS Resolution from the MID Host

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In this lesson, you will learn:

  • Why DNS matters for Discovery
  • What to check from the MID host
  • What bad DNS looks like

🔁 Quick look back: Last time: Tracking Prerequisites and Chasing Blockers. You learned how to track prerequisites and re-plan when one slips.

1 The Problem: Bad DNS Gives CIs the Wrong Names

Discovery often uses DNS to name what it finds. On a past project:

  • Old DNS records named a new server after a retired one.
  • Some IPs had no name at all.

🎯 The problem: Bad DNS gives CIs the wrong names, and names drive matching.

👉 The fix: Check DNS from each MID Server host before scanning.

Table of DNS checks and results.
Figure 1. DNS checks from snwr-mid-mum-01.

2 What to check

Key term: Forward lookup

Name to IP address.

Key term: Reverse lookup

IP address to name.

  • Pick a few known servers in each zone.
  • Check forward and reverse lookups from the MID host.
  • Note missing or wrong names.

3 Fixing problems

DNS belongs to the client’s network team. Report wrong records to them. Don’t work around them in ServiceNow.

4 Project Clear View: How We Implemented It

📍 Situation: The Mumbai MID Server hosts were ready.

🧭 Decision: Check DNS from them before any scan.

🛠️ Steps we took:

  1. Ran forward and reverse lookups for ten servers.
  2. Found one IP still named after a retired fax server.
  3. Sent it to Ravi, who fixed the record.
  4. Repeated the check from snwr-mid-lon-01 in week 6.

✅ What we verified:

  • All test lookups now return the right names.
  • The check is part of the readiness check.

📁 Evidence: DNS check results, PR-11 in the tracker.

5 Quick recap

  • Discovery often uses DNS to name CIs.
  • Check forward and reverse lookups from each MID host.
  • Report wrong records to the network team.
  • Don’t work around bad DNS in ServiceNow.

6 Check yourself

Think of your answer first. Then tap to check.

1 What’s a reverse lookup? Show answer

Finding the name for an IP address.

2 Why does bad DNS matter? Show answer

It gives CIs wrong names, and names affect matching.

3 Who fixed SNWR’s wrong record? Show answer

Ravi Iyer.

Nice work! SNWR’s DNS is checked. 🎉
Next up: Validating Network Connectivity Before Discovery

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