DNS cache problem

[Kevin Darcy]

dfwns1.airband.net and dfwns2.airband.net are publishing a 1 day (86400
second) TTL for the zyvex.com NS records. Note that the SOA record has
no direct role in determining how long nameservers cache positive
answers to queries of the zone. It only has an *in*direct role if the
zone administrator is still relying on the SOA to establish the default
TTL value for all records in the zone, but for some time now the
$TTL directive has been the preferred method of establishing default
TTL values for zones.


- Kevin

Mike Weller wrote:

> Hi,
>
> Our company is currently in the process of changing ISPs.  I gave the
> new provider my DNS zone file with the current IP# settings, and
> instructed them to set the "minimum TTL" to 10-15 minutes.  This way,
> the transition would be smooth for when we switch over the actual
> IP#s.
>
> Well, after I changed the DNS authority for our domain (zyvex.com) at
> networksolutions to the new ISP, I noticed that the new ISPs SOA
> record was corrupt! (this was last Friday night).
>
> > set type=SOA
> > zyvex.com
> Server:  dfwns1.airband.net
> Address:  206.50.26.195
> *** dfwns1.airband.net can't find zyvex.com: Non-existent host/domain
>
> Yet, the A, MX and NS records were intact:
> > set type=NS
> > zyvex.com
> Server:  dfwns1.airband.net
> Address:  206.50.26.195
> <snip>
> Authoritative answers can be found from:
> dfwns1.airband.net      internet address = 206.50.26.195
> dfwns2.airband.net      internet address = 206.50.26.196
>
> > set type=MX
> > zyvex.com
> <snip>
> zyvex.com       preference = 10, mail exchanger = mail.zyvex.com
>
> 12 hours later (after trying to desperately get a hold of them),
> they fixed the problem, and set the TTL to 1 hour (this was
> Saturday at about noon).
>
> > set type=SOA
> > zyvex.com
> Server:  gordon.chem.wayne.edu
> Address:  141.217.26.2
>
> Non-authoritative answer:
> zyvex.com
>         origin = dfwns1.airband.net
>         mail addr = hostmaster.airband.net
>         serial = 2001120101
>         refresh = 3600 (1H)
>         retry   = 900 (15M)
>         expire  = 3600000 (3600000)
>         minimum ttl = 3600 (1H)
>
> Authoritative answers can be found from:
> zyvex.com       nameserver = dfwns1.airband.net
> zyvex.com       nameserver = DFWNS2.airband.net
> dfwns1.airband.net      internet address = 206.50.26.195
> DFWNS2.airband.net      internet address = 206.50.26.196
>
> Now here's my problem.  As a test, I asked them to change 1
> unimportant hostname's IP in their DNS table.  I verified
> that the hostname changed on their DNS server (dfwns1.airband.net):
>
> Server:  dfwns1.airband.net
> Address:  206.50.26.195
> Name:    zyric.zyvex.com
> Address:  216.138.97.43
>
> Before the change, I polled a dozen nameservers around the world
> for zyric.zyvex.com:
> nslookup zyric.zyvex.com  140.221.9.6
> nslookup zyric.zyvex.com 141.217.90.3
> nslookup zyric.zyvex.com 141.217.1.13
> nslookup zyric.zyvex.com 141.217.1.15
> nslookup zyric.zyvex.com 206.191.74.19
> nslookup zyric.zyvex.com 24.226.1.11
>
> The change was made at 12pm cst today (Monday).
> 3 hours later, all nameservers still report the old IP
> (64.241.222.34), despite the minimum TTL of 1 hour.
>
> My question to you DNS experts is, if an SOA record is corrupt (and
> thus, can't read the cache time) how long does the nameserver cache
> IPs for?  Is there a way to poll "bind" to determine what the
> cache times are for any particular IP or domain?
>
> I hope it's not too long, because our current ISP is about to drop
> our service!
>
> Thanks for any help you can provide.
>
> -Mike
>
> --
> Michael J. Weller, M.Sc.               office: (972) 235-7881 x.242
> weller at zyvex.com                         cell: (214) 616-6340
> Zyvex Corp., 1321 N Plano           facsimile: (972) 235-7882
> Richardson, TX 75081                      icq: 6180540