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Re: [DNSOP] CNAME chain length limits

John R Levine <johnl@taugh.com> Wed, 27 May 2020 19:26 UTC

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Date: Wed, 27 May 2020 15:26:23 -0400
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From: John R Levine <johnl@taugh.com>
To: Eric Orth <ericorth@google.com>
Cc: dnsop <dnsop@ietf.org>
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Subject: Re: [DNSOP] CNAME chain length limits
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>> While I should have been doing something else, I made a rather long CNAME
>> chain.  When I looked up chain.examp1e.com it got SERVFAIL, but after I
>> warmed up my cache five links at a time by looking for chain5, chain10,
>> chain15, and so forth, it worked.  At least it worked in "dig" and "host".
>> When I try and look up http://chain.examp1e.com, Chrome waits a while
>> and says not found,
>
> If Chrome is using its built-in stub, there's not expected to be a limit
> (other than the overall message size limits), but nothing tests chains this
> long other than security fuzzers that are only looking for crashes or
> memory issues.

On my Mac, I get surprisingly consietent browser results.  In Chrome, 
Firefox, and Safari, chain10.examp1e.com works, chain11.examp1e.com fails 
slowly.  From the TTLs I get from dig, it appears that none of them are 
using the resolver to follow the CNAME chains.  For Firefox I have the 
canary domain blocked so I dunno what it is doing.

>> chain12.examp1e.com.    3449    IN      CNAME   chain11.examp1e.com.
>> chain11.examp1e.com.    3486    IN      CNAME   chain10.examp1e.com.
>> chain10.examp1e.com.    3455    IN      CNAME   chain9.examp1e.com.
>> chain9.examp1e.com.     3455    IN      CNAME   chain8.examp1e.com.
>> chain8.examp1e.com.     3455    IN      CNAME   chain7.examp1e.com.
>> chain7.examp1e.com.     3455    IN      CNAME   chain6.examp1e.com.
>> chain6.examp1e.com.     3455    IN      CNAME   chain5.examp1e.com.
>> chain5.examp1e.com.     3455    IN      CNAME   chain4.examp1e.com.
>> chain4.examp1e.com.     3455    IN      CNAME   chain3.examp1e.com.
>> chain3.examp1e.com.     3455    IN      CNAME   chain2.examp1e.com.
>> chain2.examp1e.com.     3455    IN      CNAME   chain1.examp1e.com.
>> chain1.examp1e.com.     3466    IN      CNAME   chain0.examp1e.com.
>> chain0.examp1e.com.     3460    IN      A       64.57.183.119

Regards,
John Levine, johnl@taugh.com, Taughannock Networks, Trumansburg NY
Please consider the environment before reading this e-mail. https://jl.ly

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