Ascend Archive
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Re: (ASCEND) DNS resolution bug
At 09:27 AM 5/8/98 -0700, Kit Knox wrote:
>
>There appears to be a problem with Ascend's DNS resolution code and hosts
>with many A records. Could people with a minute to spare please do the
>following :
>
>1. Telnet to any Ascend router.
>2. Enter term serv mode.
>3. Attempt to ping/traceroute to www.microsoft.com.
>4. Record if the DNS lookup fails.
>5. Let me know which nameserver you are using and what version of Bind it
>is running.
The problem is an old one that has just surfaced on our products. It's
been around as Kit observes on other (including UNIX) platforms for a
while. It relates to a section of the relevant RFC - where DNS replies
of over 512 bytes is addressed.
Conclusion so far...
DNS is normally a UDP based protocol, however if the reply is longer than
512 bytes, the RFC recommends establishing a TCP connection. This is not a
widely implemented portion of the RFC, as few DNS lookups require more than
512 byte responses.
We have considered processing what we could (the first 512 bytes) and
ignoring the TC bit. But that could have unpredictable consequences.
The alternative is also unpredictable, since virtually no one else supports
the TCP option, even if we did, it most likely wouldn't work.
Kevin
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