Subject: Re: [ISC-Bugs #36330] [PATCH 3/3] use a larger starting EDNS UDP size, and add some debug logging
In-Reply-To: Your message of "Fri, 25 Jul 2014 14:45:44 +0000." <rt-3.8.6-35138-1406299544-1900.36330-4-0@isc.org>
Date: Mon, 04 Aug 2014 12:14:07 +1000
References: <RT-Ticket-36330@isc.org> <alpine.LSU.2.00.1406191110370.3035@hermes-1.csi.cam.ac.uk> <E1XAgke-0002LU-Ff@hermes-1.csi.cam.ac.uk> <rt-3.8.6-35138-1406299544-1900.36330-4-0@isc.org>
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Message-ID: <20140804021407.52C9E1B76D77@rock.dv.isc.org>
To: bind9-bugs@isc.org
From: Mark Andrews <marka@isc.org>
RT-Message-ID: <rt-3.8.6-35151-1407118455-53.36330-0-0@isc.org>
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This one will break lookups from behind a firewall that only passes DNS
queries <= 512 bytes.  This can be demonstrated by having named silently
drop any UDP packets > 512 bytes.

	named -T maxudp512

B.T.W.
	The broken TCP behaviour of the nameservers for soy and foo has
been fixed.

Mark

In message <rt-3.8.6-35138-1406299544-1900.36330-4-0@isc.org>, "Tony Finch via 
RT" writes:
> ---
>  lib/dns/resolver.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/lib/dns/resolver.c b/lib/dns/resolver.c
> index 884aeb8..0b48d1a 100644
> --- a/lib/dns/resolver.c
> +++ b/lib/dns/resolver.c
> @@ -2022,10 +2022,10 @@ resquery_send(resquery_t *query) {
>  
>  			/*
>  			 * We know nothing about the peer's capabilities
> -			 * so start with minimal EDNS UDP size.
> +			 * so start with moderate EDNS UDP size.
>  			 */
>  			if (udpsize == 0U)
> -				udpsize = 512;
> +				udpsize = 1232;
>  
>  			if ((flags & DNS_FETCHOPT_EDNSVERSIONSET) != 0) {
>  				version = flags & DNS_FETCHOPT_EDNSVERSIONMASK;
> @@ -2103,6 +2103,8 @@ resquery_send(resquery_t *query) {
>  	 * Record the UDP EDNS size choosen.
>  	 */
>  	query->udpsize = udpsize;
> +	isc_log_write(dns_lctx,	DNS_LOGCATEGORY_RESOLVER, DNS_LOGMODULE_RESOLVE
> R,
> +	    ISC_LOG_DEBUG(10), "fctx %p(%s): udpsize %d", fctx, fctx->info, udp
> size);
>  
>  	if (udpsize > 0)
>  		add_triededns(fctx, &query->addrinfo->sockaddr);
> -- 
> 2.0.1
> 
> 
> 
> 
> -- 
> Ticket History: https://bugs.isc.org/Ticket/Display.html?id=36330
-- 
Mark Andrews, ISC
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: +61 2 9871 4742                 INTERNET: marka@isc.org