Re: Caching SERVFAIL?

My experience with caching SERVFAIL, I lost connectivity for a day.

From time to time but at least once per day my isp is breaking my aDSL session.

When my router does not reconnect fast enough or when there is an outage
all queries will fail and get cached. After about 10 minutes the internet
is dead for the rest of the day. Of coarse killing dnscache works much
faster.

Cheers
Peter


Mark Johnson wrote:
> On Tue, Mar 24, 2009 at 6:41 PM, Matthew Dempsky <[email protected]> wrote:
>> dnscache before djbdns-1.05 used to cache SRVFAIL responses (with
>> support for actually caching them as SRVFAIL, rather than turning them
>> into NXDOMAIN).  Dan specifically removed this from djbdns-1.04, with
>> a CHANGES comment "dnscache no longer caches SERVFAIL. per-ip is
>> obviously the way to go."
> 
> Relevant bits from CHANGES from djbdns-1.05:
> 
> 20010106
>         version: djbdns 1.03.
> 20010113
>         <snip>
>         ui: dnscache no longer caches SERVFAIL. per-ip is obviously the
>                 way to go.
>         <snip>
> <snip>
> 20010121
>         version: djbdns 1.04.
> 
> Here's the relevant bits from a diff between djbdns-1.03 and djbdns-1.04:
> 
> diff -r djbdns-1.03/log.c djbdns-1.04/log.c
> 178,183d177
> < void log_cachedservfail(const char *dn)
> < {
> <   string("cached servfail "); name(dn);
> <   line();
> < }
> <
> diff -r djbdns-1.03/log.h djbdns-1.04/log.h
> 18d17
> < extern void log_cachedservfail(const char *);
> diff -r djbdns-1.03/query.c djbdns-1.04/query.c
> 200d199
> <     cachegeneric(DNS_T_AXFR,z->name[z->level],"",0,60);
> 254,260d252
> <     byte_copy(key,2,DNS_T_AXFR);
> <     cached = cache_get(key,dlen + 2,&cachedlen,&ttl);
> <     if (cached) {
> <       log_cachedservfail(d);
> <       goto SERVFAIL;
> <     }
> <
> 
> Hi Jos!
> 
> http://marc.info/?l=djbdns&m=108560819606350&w=2
> 
> Questions, Queries, Posers:
> 
> Why the change?  What's with the DNS_T_AXFR?  I'll take a stab at the
> former and guess maybe that the downside from a cached SERVFAIL
> (bounced mail, etc) was determined to be worse than the performance
> benefit of not repeatedly trying to contact horked servers?
> 
> What do other recursive resolvers do?  I'll go stare at the code
> eventually, but if anybody knows, save me the trouble...

-- 
Peter and Karin Dambier
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