override ttl=0

Thu Jan 3 01:50:55 UTC 2008

Well, it *shouldn't* be included in BIND, in my opinion. If a DNS record 
comes from an authoritative source with TTL=0 then it is to be treated 
as highly dynamic, literally able to change from second to second. The 
resolver shouldn't be holding onto data that it's been told is extremely 
mutable. To do so risks defeating whatever load-balancing mechanisms the 
domain owner has in place.

If you *really* need functionality like this, then set up a "fake" 
version of the zone in question, query the real zone periodically, and 
then update your fake version dynamically. At least then you contain 
this ugliness within the normal nameserver/resolver constructs.

By the way, the document you linked to in your previous message makes 
mention of the fact that TTLs are set to 0 when an address is allocated 
at the time of query (which I interpret to mean *dynamically*), but also 
talks about static translation. Could it be that the TTL=0 problem is 
just a side effect of your network architecture? Or, if Cisco is dumb 
enough to set TTL=0 blindly and unconditionally, everyone who uses the 
product should be complaining to them about it.

                                       - Kevin

Herve Guehl wrote:
> Hi,
> Could such a feature be included in bind ?
> regards
> Hervé
>
> On Dec 22, 2007 8:56 AM, Herve Guehl <herve.guehl at gmail.com> wrote:
>
>   
>> Unfortunatly, The manufacturer is CISCO... http://www.cisco.com/en/US/products/ps6553/products_white_paper09186a008011ff51.shtml
>>
>> It's a pain when your working with partners that use this
>> technology...(Obviously I have no choice and bo weight about it :) )
>>
>> regard.
>> Herve Guehl
>>
>>
>>
>> On Dec 21, 2007 10:51 PM, Mark Andrews <Mark_Andrews at isc.org> wrote:
>>
>>     
>>>> Hi everybody,
>>>> I'm getting troubles with a DNS-ALG machine that send ttl=0 for every
>>>> question I send to it.
>>>> I browsed archive but did not find any solution to my problem.
>>>> I just need to override ttl for A record when the ttl=0.
>>>> Here a patch for bind 9.3.3rc2 (redhat 5.0).
>>>> I know, that TTL should not be overrided, but in some case this
>>>> functionality can be helpfull.
>>>>         
>>>        Tell us the manufacture of the DNS-ALG so we can all avoid
>>>        such a broken product.  The DNS requires caching to work.
>>>        Any DNS-ALG that don't pass on the TTL is broken.
>>>
>>>       
>>>> The status of this patch is 'works for me'.
>>>>
>>>> Please let me know if there is another implementation
>>>>
>>>> Regard
>>>> Hervé Guehl
>>>>
>>>> Note : dont blame me if i'm not using the right list, just say me
>>>>         
>>> where I
>>>       
>>>> should write
>>>>
>>>>
>>>>
>>>> diff -urN bind-9.3.3rc2.ori/bin/named/server.c bind-9.3.3rc2
>>>> /bin/named/server.c
>>>> --- bind-9.3.3rc2.ori/bin/named/server.c        2006-05-24 06:30:
>>>> 24.000000000 +0200
>>>> +++ bind-9.3.3rc2/bin/named/server.c    2007-12-18 22:01:47.000000000+0100
>>>> @@ -1245,6 +1245,11 @@
>>>>         result = ns_config_get(maps, "max-cache-ttl", &obj);
>>>>         INSIST(result == ISC_R_SUCCESS);
>>>>         view->maxcachettl = cfg_obj_asuint32(obj);
>>>> +
>>>> +       obj = NULL;
>>>> +       result = ns_config_get(maps, "override-zero-cache-ttl", &obj);
>>>> +       INSIST(result == ISC_R_SUCCESS);
>>>> +       view->overridezerocachettl = cfg_obj_asuint32(obj);
>>>>
>>>>         obj = NULL;
>>>>         result = ns_config_get(maps, "max-ncache-ttl", &obj);
>>>> diff -urN bind-9.3.3rc2.ori /lib/dns/include/dns/view.h bind-9.3.3rc2
>>>> /lib/dns/include/dns/view.h
>>>> --- bind-9.3.3rc2.ori/lib/dns/include/dns/view.h        2004-03-10
>>>>         
>>> 03:55:
>>>       
>>>> 58.000000000 +0100
>>>> +++ bind-9.3.3rc2/lib/dns/include/dns/view.h    2007-12-18 22:02:
>>>> 01.000000000 +0100
>>>> @@ -116,6 +116,7 @@
>>>>         isc_boolean_t                   requestixfr;
>>>>         isc_boolean_t                   provideixfr;
>>>>         dns_ttl_t                       maxcachettl;
>>>> +       dns_ttl_t                       overridezerocachettl;
>>>>         dns_ttl_t                       maxncachettl;
>>>>         in_port_t                       dstport;
>>>>         dns_aclenv_t                    aclenv;
>>>> diff -urN bind-9.3.3rc2.ori/lib/dns/resolver.c bind-9.3.3rc2
>>>> /lib/dns/resolver.c
>>>> --- bind-9.3.3rc2.ori/lib/dns/resolver.c        2006-08-31 05:57:
>>>> 11.000000000 +0200
>>>> +++ bind-9.3.3rc2 /lib/dns/resolver.c    2007-12-18 22:02:56.000000000+0100
>>>> @@ -3537,6 +3537,11 @@
>>>>                         rdataset->ttl = res->view->maxcachettl;
>>>>
>>>>                 /*
>>>> +                 * HGU configure minimum ttl if ttl=0 for A record
>>>> +               */
>>>> +               if  ( (rdataset->ttl == 0) && (rdataset->type ==
>>>> dns_rdatatype_a) )
>>>> +                        rdataset->ttl > > res->view->overridezerocachettl;
>>>> +               /*
>>>>                  * If this rrset is in a secure domain, do DNSSEC
>>>>         
>>> validation
>>>       
>>>>                  * for it, unless it is glue.
>>>>                  */
>>>> diff -urN bind-9.3.3rc2.ori /lib/isccfg/namedconf.c bind-9.3.3rc2
>>>> /lib/isccfg/namedconf.c
>>>> --- bind-9.3.3rc2.ori/lib/isccfg/namedconf.c    2006-03-02 01:37:
>>>> 20.000000000 +0100
>>>> +++ bind-9.3.3rc2/lib/isccfg/namedconf.c        2007-12-19 15:11:
>>>> 49.000000000 +0100
>>>> @@ -715,6 +715,7 @@
>>>>         { "lame-ttl", &cfg_type_uint32, 0 },
>>>>         { "max-ncache-ttl", &cfg_type_uint32, 0 },
>>>>         { "max-cache-ttl", &cfg_type_uint32, 0 },
>>>> +       { "override-zero-cache-ttl", &cfg_type_uint32, 0 },
>>>>         { "transfer-format", &cfg_type_transferformat, 0 },
>>>>         { "max-cache-size", &cfg_type_sizenodefault, 0 },
>>>>         { "check-names", &cfg_type_checknames, CFG_CLAUSEFLAG_MULTI },
>>>>
>>>>
>>>>         
>>> --
>>> Mark Andrews, ISC
>>> 1 Seymour St., Dundas Valley, NSW 2117, Australia
>>> PHONE: +61 2 9871 4742                 INTERNET: Mark_Andrews at isc.org
>>>
>>>       
>>     
>
>
>
>
>   