Re: [dnsext] compression in UPDATE

[Mark Andrews <[e-mail]>]

In message <[e-mail]>, Brian Wellington
 writes:
> 
> On May 9, 2011, at 1:26 PM, Paul Vixie wrote:
> 
> >> Date: Mon, 9 May 2011 16:03:59 -0400
> >> From: Edward Lewis <[e-mail]>
> >> 
> >>> so i see.  ouch.  in fact the bind8 version of this goes well beyond
> >>> RFC 3597's constraints on "known types".  i suggest that we draw a new
> >>> line in the sand and require that compression be understood for all
> >>> types that any now-current implementation is known to compress for.
> >> 
> >> I'd go the other way.  There's little harm in never compressing an outgoin
> g
> >> message (the loss is that extra octets are moved).  There's more harm in
> >> compressing a type the receiver doesn't know, especially because the
> >> receiver wouldn't know that there was compression in use. (Compression
> >> isn't transitive, message to message, that is.)
> > 
> > i agree, and that was my first inclination also, but i hate breaking the
> > installed base just for the sake of purity.  nsupdate is a huge contributor
> > to the world's supply of UPDATE messages and i am loathe to declare it
> > broken.
> 
> A few more points:
> 
> RFC 1035 (in section 4.1.4. Message compression) doesn't say anything about o
> pcode.  UPDATE was defined later, so obviously wouldn't be mentioned there, b
> ut there's also no specific mention of QUERY, IQUERY, or STATUS; the text say
> s "In order to reduce the size of messages".
> 
> RFC 1996 (NOTIFY) also doesn't mention compression; is anyone suggesting that
>  compression be outlawed there as well?
> 
> RFC 3597 (unknown RR types) doesn't mention anything about opcode QUERY; I'd 
> interpret it as defining the list of types expected to be known regardless of
>  OPCODE.  If bind8's nsupdate is compressing types not listed by RFC3597, tha
> t sounds like a potential problem, but compressing any type listed in RFC 359
> 7 seems safe enough.
> 
> Brian

BIND 8's nsupdate knows about the following types. 

        { "a",          T_A },     	/* no rdata compression possible */
        { "ns",         T_NS },		/* listed in RFC 3597 */
        { "cname",      T_CNAME },	/* listed in RFC 3597 */
        { "soa",        T_SOA },	/* listed in RFC 3597 */
        { "mb",         T_MB },		/* listed in RFC 3597 */
        { "mg",         T_MG },		/* listed in RFC 3597 */
        { "mr",         T_MR },		/* listed in RFC 3597 */
        { "null",       T_NULL },	/* no rdata compression possible */
        { "wks",        T_WKS },	/* no rdata compression possible */
        { "ptr",        T_PTR },	/* listed in RFC 3597 */
        { "hinfo",      T_HINFO },	/* no rdata compression possible */
        { "minfo",      T_MINFO },	/* listed in RFC 3597 */
        { "mx",         T_MX },		/* listed in RFC 3597 */
        { "txt",        T_TXT },	/* no rdata compression possible */
        { "rp",         T_RP },		/* listed in RFC 3597 */
        { "afsdb",      T_AFSDB },	/* listed in RFC 3597 */
        { "x25",        T_X25 },	/* no rdata compression possible */
        { "isdn",       T_ISDN },	/* no rdata compression possible */
        { "rt",         T_RT },		/* listed in RFC 3597 */
        { "nsap",       T_NSAP },	/* no rdata compression possible */
        { "nsap_ptr",   T_NSAP_PTR }, /* SHOULD HAVE BEEN LISTED IN RFC 3597 */
        { "sig",        T_SIG },	/* listed in RFC 3597 */
        { "key",        T_KEY },	/* no rdata compression possible */
        { "px",         T_PX },		/* listed in RFC 3597 */
        { "loc",        T_LOC },	/* no rdata compression possible */
        { "nxt",        T_NXT },	/* listed in RFC 3597 */
        { "eid",        T_EID },
        { "nimloc",     T_NIMLOC },
        { "srv",        T_SRV },	/* listed in RFC 3597 */
        { "atma",       T_ATMA },
        { "naptr",      T_NAPTR },	/* listed in RFC 3597 */
        { "kx",         ns_t_kx },	/* listed in RFC 3597 */
        { "cert",       ns_t_cert },	/* no rdata compression possible */
        { "aaaa",       ns_t_aaaa },	/* no rdata compression possible */
        { "dname",      ns_t_dname },   /* listed in RFC 3597 */

This all being said, case sensitive, compression should be used so
that UPDATE can meet the case preservation requirements of RFC103[45].

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Mark Andrews, ISC
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