DNS Session 2: Operation of recursive (caching) nameserver
Table of Contents
DNS Session 2: Operation of recursive (caching) nameserver
How caching NS works (1)
What if the answer is not in the cache?
How caching NS works (2)
How does it know which auth nameserver to ask?
Intermediate nameservers return a "NS" resource record
Eventually this process will either:
How does this process start?
Distributed systems have many points of failure!
Caching reduces the load on auth nameservers
Example 1: www.tiscali.co.uk (on an empty cache)
Example 2: smtp.tiscali.co.uk (after previous example)
Caches can be a problem if data becomes stale
The owner of an auth server can control how their data is cached
A compromise policy
What sort of problems might happen when a caching nameserver is operating?
(1) One authoritative server is down or unreachable
(2) *ALL* authoritative servers are down or unreachable!
(3) Referral points to a nameserver which is not authoritative for this zone
(4) Inconsistencies between authoritative servers
(5) Inconsistencies in delegations
(6) Mixing caching and authoritative nameservers
(7) Inappropriate choice of parameters
These problems are not the fault of the caching server!
How to debug these problems?
How to interpret responses (1)
How to interpret responses (2)
How to debug a domain using "dig +norec" (1)
How to debug a domain using "dig +norec" (2)
How to debug a domain using "dig +norec" (3)
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