Re: [dnsop] WGLC on draft-ietf-dnsop-bad-dns-res-03.txt

[Kevin Darcy <[e-mail]>]

Peter Koch wrote:

>>Please clearly state to the mailing list whether you support or oppose
>>this draft going to the IESG.
>>    
>>
>
>While I consider this a very valuable document which could serve implementers
>of resolvers and the stability of the DNS as a whole, here are some remarks
>and questions, which make me think the document is not yet ready for
>publication.
>
>  
>
>>   domain (TLD) name servers.  In some cases we recommend minor
>>   additions to the DNS protocol specification and corresponding changes
>>   in iterative resolver implementations to alleviate these unnecessary
>>    
>>
>
>This promise would probably not warrant the BCP but instead the standards
>track. However, as far as I understood the recommendations they are all
>guidelines for resolver implementors and (recursive) server operators, so BCP
>is OK.
>However, I'd suggest the wording be changed to reflect that the standard
>itself, i.e. the on-the-wire protocol, remains unchanged. These are guidelines.
>
>  
>
>>   rate.  Some of the changes recommended affect the core DNS protocol
>>   specification, described principally in RFC 1034 [2], RFC 1035 [3]
>>   and RFC 2181 [4].
>>    
>>
>
>Since I may have missed those changes, could they please be clearly identified?
>
>  
>
>>   answer questions about certain zones authoritatively.  Often called a
>>   "recursive name server" or a "caching name server", it is in fact an
>>   iterative resolver combined with an authoritative name server.
>>    
>>
>
>Shouldn't that read 'a non-authoritative name server', since the cache fed by
>the iterative resolver serves non-auth data?
>
No, this sentence describes a DNS entity that is (in the historical 
terminology) master or slave for one or more zones (i.e. an 
"authoritative name server"), yet supports recursive querying (i.e. an 
"iterative resolver"). It's a combination of two different roles in a 
single entity. I think the wording is fine as it stands.

>>2.1  Aggressive requerying for delegation information
>>
>>   There can be times when every name server in a zone's NS RRset is
>>   unreachable (e.g., during a network outage), unavailable (e.g., the
>>   name server process is not running on the server host) or
>>    
>>
>
>... or the host does not exist (name doesn't resolve) ...
>
>  
>
>>   For this query of the parent zone to be useful, the target zone's
>>   entire set of name servers would have to change AND the former set of
>>   name servers would have to be deconfigured or decommissioned AND the
>>   delegation information in the parent zone would have to be updated
>>   with the new set of name servers, all within the TTL of the target
>>   zone's NS RRset.  We believe this scenario is uncommon:
>>   administrative best practices dictate that changes to a zone's set of
>>   name servers happen gradually when at all possible, with servers
>>   removed from the NS RRset left authoritative for the zone as long as
>>   possible.  The scenarios that we can envision that would benefit from
>>   the parent requery behavior do not outweigh its damaging effects.
>>    
>>
>
>Explicit "NS" queries should never happen (there were some implicit assumptions
>in this direction during the discussion of wildcard NS RRs), but there are
>situations where some requery can be justified:
>
>1) When the NS-RRset in the parent zone is larger than that sent
>   authoritatively from within the zone, additional information may be
>   discovered. This is a configuration problem, of course, but is not too
>   uncommon.
>
>2) More importantly, consider a cache content like this:
>
>	example.com.		NS	dns.example.com.
>				NS	dns.example.net.
>	dns.example.net.	A	192.0.2.42
>
>   The dns.example.com A RR has expired. Now, if dns.example.net is not
>   available, the zone is 'non-responsive'. To learn the address of
>   dns.example.com. there's no other way than to make use of the necessary
>   glue RR present in the COM zone, so there is justification for going
>   one step up. Another recommendation following from this could be that the
>   address records of nameservers in or below the zone served should not have
>   TTLs lower than the NS RRs.
>
>  
>
>>2.1.1  Recommendation
>>
>>   An iterative resolver MUST NOT send a query for the NS RRset of a
>>   non-responsive zone to any of the name servers for that zone's parent
>>   zone.  For the purposes of this injunction, a non-responsive zone is
>>   defined as a zone for which every name server listed in the zone's NS
>>   RRset:
>>   1.  is not authoritative for the zone (i.e., lame), or,
>>   2.  returns a server failure response (RCODE=2), or,
>>   3.  is dead or unreachable according to section 7.2 of RFC 2308 [5].
>>    
>>
>
>This recommendation now can be adjusted accordingly. Explicit NS type queries
>can be recommended against reagrdless of the responsiveness of the zone. They
>have no place in the resolution process, do they?
>
There's nothing wrong with doing explicit type NS queries in the course 
of troubleshooting. Please make sure that any language deprecating 
explicit NS type queries makes clear that it only applies to the 
generation of such queries as part of the regular resolution process.

>>2.2.1  Recommendation
>>
>>   Iterative resolvers SHOULD cache name servers that they discover are
>>    
>>
>
>s/cache name servers/cache the status of name servers/;
>
>  
>
>>   not authoritative for zones delegated to them (i.e.  lame servers).
>>   Lame servers MUST be cached against the specific query tuple <zone
>>   name, class, server IP address>.  Zone name can be derived from the
>>   owner name of the NS record that was referenced to query the name
>>   server that was discovered to be lame.  Implementations that perform
>>   lame server caching MUST refrain from sending queries to known lame
>>   servers based on a time interval from when the server is discovered
>>   to be lame.  A minimum interval of thirty minutes is RECOMMENDED.
>>    
>>
>
>In general I support this recommendation. Here's a corner case:
>
>	dns.example.com is delegated (and detected) lame example.com but
>	is authoritative for sub.example.net 
>
>During resolving www.sub.example.net dns.example.com must be skipped but upon
>receipt of the referral containing the reference to dns.example.com it should
>be eligible again. The problem is that one cannot tell in advance whether
>www.sub.example.net is part of the example.net zone. The recommendation
>could be given more precisely:
>
>  old:	MUST refrain from sending queries to known lame servers
>
>  new:	MUST refrain from sending queries whose QNAME is likely to be in the
>	lame zone (i.e. equals the zone name or is below the zone name and not
>	positively identified to belong to a distinct zone) to known lame
>	servers
>
>  
>
>>2.3  Inability to follow multiple levels of out-of-zone glue
>>    
>>
>
>In this paragraph the term glue is used where 'additional data' would be more
>precise.
>
>  
>
>>   new gTLDs will use name servers in other gTLDs, increasing the amount
>>   of inter-zone glue.
>>    
>>
>
>Again, that's not glue then. s/glue/additional data/
>
>  
>
>>2.4  Aggressive retransmission when fetching glue
>>    
>>
>
>  
>
>>   implementations take this address inclusion a step further with a
>>   feature called "glue fetching".  A name server that implements glue
>>    
>>
>
>While at least one popular implementation called this 'fetch-glue', it's
>actually just additional section processing. Glue is just there (or it isn't),
>it can't be fetched. That should have been clarified by the AXFR draft, but
>that's unfortunately in some indetermined state.
>Sorry for the nitpicking here, but fuzzy or changing use of wording is
>extremely counterproductive in educating DNS operators. And yes, that does
>matter since they are part of our target audience here. So please let's
>use 'additional data processing' in favor of 'glue'.
>
>The overall recommendation is fine, though.
>
>  
>
>>2.6.1  Recommendation
>>
>>   An authoritative server can detect this situation.  A trailing dot
>>   missing from an NS record's RDATA always results by definition in a
>>   name server name that exists somewhere under the SOA of the zone the
>>    
>>
>
>I'd prefer the term 'zone apex' over SOA, since the latter is just an RR type.
>
Strongly agreed. SOA and zone apex are *not* interchangeable terms. This 
is one of my pet peeves and I'm surprised I didn't notice it in my 
previous readings of this ID.

>>   NS record appears in.  Note that further levels of delegation are
>>   possible, so a missing trailing dot could inadvertently create a name
>>   server name that actually exists in a subzone.  But in any case, the
>>   address record must still be present in this zone, either as
>>   authoritative data or glue.
>>    
>>
>
>I disagree with this analysis. Given the zone
>
>	example.net.	NS	dns.example.net
>			->	dns.example.net.example.net.
>
>Now, if a delegation at example.net.example.net. or net.example.net. exists,
>there's no need that dns.example.net.example.net. be one of the authoritative
>servers, so the absence of a glue A RR does not indicate that the name
>dns.example.net.example.net. does not exist. So, not only doesn't it have to
>exist in the zone, it also need not be part of the zone file (using the AXFR
>draft logic).
>
>  
>
>>   An authoritative name server SHOULD report an error when one of a
>>   zone's NS records references a name server below the zone's SOA when
>>    
>>
>
>s/zone's SOA/zone apex/
>
>  
>
>>   a corresponding address record does not exist in the zone.
>>    
>>
>
>First, I'd suggest that any slave server only issue a warning but still load
>the zone. A master should report an error if the target of the NS RR
>is below the zone apex and an address record does not exist (because the
>name is within the zone and neither A nor AAAA RRsets exist or because the
>name doesn't exist) and a warning if the domain name belongs to a child
>zone (regardless of any glue RR).
>
>  
>
>>2.7.1  Recommendation
>>
>>   Because of the additional load placed on a zone's parent's
>>   authoritative servers resulting from a zero TTL on a zone's NS RRset,
>>   under such circumstances authoritative name servers SHOULD issue a
>>   warning when loading a zone or refuse to load the zone altogether.
>>    
>>
>
>A warning is OK at both a master and a slave, otherwise a slave should not
>refuse a zone on these grounds. Causing harm sometimes heals, but the
>slave administrator can't do much about this problem. Also, the recommendation
>should be clear in what to do (warning vs error), and a warning seems less
>invasive here. Also, refusing to load a 0 TTL zone while silently accepting
>TTLs of 1 second is probably hard to sell.
>This is registry policy, though, and could already be implemented there ...
>
>  
>
>>2.8.1  Recommendation
>>
>>   Dynamic update agents SHOULD send SOA or NS queries to progressively
>>   higher-level zones to find the closest enclosing zone for a given
>>    
>>
>
>s/zones/names/, since there's no need to send the query to higher zones.
>The actual problem is that you don't know what zone the name belongs to.
>
>  
>
>>   name to update.  Only after the appropriate zone is found should the
>>   client send an UPDATE message to one of the zone's authoritative
>>    
>>
>
>I'd restrict this recommendation to SOA queries only. NS queries are currently
>not necessary and shouldn't be introduced. 
>
See Section 4 of RFC 2136. A Dynamic Update requestor is assumed to "be 
able to determine the nameservers for th[e] zone" and to be able to 
match an SOA MNAME with an NS NSDNAME. Such statements imply the 
issuance of NS record type queries.

I support this draft going to the IESG, with the exception of the SOA -> 
zone apex editorial change mentioned above.

- Kevin

.
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