2. A Study of DNS Lameness by Ed Lewis ARIN Research Engineer
Presented by
Ray Plzak
President

3. Agenda
Definition
Purpose
Results
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4. Definitions Lameness is – an NS RR That Lameness might happen if:
Contains no address record(s)
Does not respond to queries
Responds negatively for the zone
Lameness might happen if:
Domain name has multiple addresses
Server responds non-authoritatively (recursively)
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5. Why Bother? ARIN membership raised the issue of cleaning this up
Lame delegations cause
Application Failure
Service Delay
Lame delegations can be limited easily
Intermittent network problems make it infeasible to eliminate it completely
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6. Reverse Map This effort is targeted at ARIN's reverse map delegations
ARIN's /8's
Legacy /8's
Not all /8's - not RIPE NCC, not APNIC
Dependencies are
simplifying assumptions about the parsing of the zone files
summary output breaks results into /16's and /24's
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7. Early results Remember, this is not all of in-addr.arpa...
As of July 2002
Number of NS RR's 548,667
Number of zones 231,240
Number of name server names 25,047
Number of IP unique addresses 21,846
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8. per Zone demographics Servers per zone - max 7, avg 2.37
Addresses per zone - max 26, avg 2.32
Zones with no addresses 3,062
Zones with one address 7,365
All zones have multiple NS RR's
Some lacked glue for one
Some had two names with identical glue
Some duplicates slipped through
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9. per Name Server Zones - max 5772, avg 21.9 No address - 3,178
Multiple addresses - 219
Addresses - max 24, avg not counted
Longest name 41 chars
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10. per IP
Zones - max 5772, avg 24.6
Addresses with multiple domain names pointing to them - 291
Max number of domain names pointing to an address - 9
PTR records not checked
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11. Counting By Zones Condition % Comment No IP address 1 Unreachable
One IP address 3
Multi Address 95
“the requirement”
No Working 38
Zone not reachable
One Working 10
Multi Working 52
No Broken 49
“perfect zones”
Some Broken 13
Notes
"No working" – Never a reply
"No broken" – All servers good
"Some broken“ – Some lameness
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12. Next steps Measure number of faulty NS RRs
Distribute and run from different locations
Correlate results from different network locations
Present observations to membership
Investigate the use of this data
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13. Thank You
September 2002
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