Internet Unknown (28)
Mark_Andrews at isc.org
Thu Nov 18 20:24:28 UTC 2004
> MA> The polaris.co.in nameservers are not RFC 1034 compliant (they don't
> MA> reply to EDNS (RFC 2671) queries).
> Not replying to queries is not a violation of the protocol. There's no
> way that any protocol (such as DNS) that employs an unreliable transport
> (such as UDP) can make replying to messages a requirement. It's wrong
> to say that a server that doesn't reply to queries is not complying with
> RFC 1034.
To not reply when you receive a query you don't understand is
a violation of the protocol. RFC 1034 includes error code to
tell the client that you don't understand the query. A server
is supposed to use them. To not use them is a violation of
NOTIMP is required to be sent when you get a opcode you don't
FORMERR for when you get a query that doesn't appear to be correct.
REFUSED is for when you are blocking answers for administative
SERVFAIL is the fallback error code.
A RFC 1034 compliant server should send FORMERR in reply to
a EDNS query. In practice some send NOTIMP and SERVFAIL or
just ignore the EDNS extention and just a plain DNS answer.
Then you have the servers that drop EDNS queries and for
kicks there is a vendor that refuses to answer future queries
for ~30 seconds after receiving a EDNS query so lookups
fail even after fallback to DNS on timeout.
> MA> You would think that all nameservers would handle EDNS queries by
> MA> now. After all EDNS has been on the standards track for 5 years now.
> The situation with EDNS0 is that because so few content DNS servers
> support it, the gain that EDNS0 gives from losing the DNS/TCP
> setup/teardown overhead in the small minority of cases is entirely
> offset by the loss incurred by the extra DNS/UDP traffic in the vast
> majority of cases.
> As I have said before, the irony of this is that support for EDNS0 in
> content DNS servers is comparatively easy compared to support for EDNS0
> in the back ends of resolving proxy DNS servers and in DNS Client
> libraries. If everyone merely did only the easy part of implementing
> EDNS0 support in their content DNS servers (even if only supporting
> DNS/UDP datagram sizes up to 512 octets), the current situation would be
> much improved, and enabling the use of EDNS0 in a resolving proxy DNS
> server would no longer result in a net increase in network traffic.
> MA> It only takes 1/2 a day to add support for them to a existing
> MA> server.
> That's a facile assertion. How long it takes to add EDNS0 support
> obviously depends from the particular server software. As I said, it
> also depends from the type of the server software.
If you are capable of writing a DNS server the work required to
implement and test EDNS support is about 1/2 a day. It is much
less in authoritative only servers.
Mark Andrews, ISC
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: +61 2 9871 4742 INTERNET: Mark_Andrews at isc.org
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