[anti-abuse-wg] DNS DoS attacks by 91.235.143.158 and 69.162.110.100

For several weeks now our DNS server gets attacked by the following 2 systems.
It's a DoS attack. We have DNS recursion disabled, but these systems
countlessly send recursion queries.
We now are blocking them at the firewall level:

pkts bytes target     prot opt in     out     source               destination
1845K  118M DROP       all  --  *      *       91.235.143.158       0.0.0.0/0
1518K  100M DROP       all  --  *      *       69.162.110.100       0.0.0.0/0

We have sent the first one 4 Abuse Reports, and the seconds one 10 (!) ARs,
and also had email contact to both their admins/abuse team. But nothing changes.
Their cheap excuse is by saying that our DNS server is allegedly an
open resolver (this is total BS! it's untrue), and the attack would
be a so called "reflected UDP DNS attack" carried out by someone else
using forged IP headers (IMO again cheap BS excuse as nowadays
every ISP uses egress/ingress filtering to block such SenderIP-forgeries).

My suspicion is that these companies are maybe specialized (and get paid for)
to carry out such DNS attacks to bring down the network infrastructure of target systems.
It seems they try to poison our DNS cache. This of course would affect our whole infrastructure.

The IPs belong to these domains/companies:

91.235.143.158 (Ukraine --> RIPE): belongs to the operators of www.irishindependentescorts.com ,
  a porno site operated/administered by a David Walsh <david at irishindependentescorts.com>
  and davidwalsheire at gmail.com, AbuseAdress: support at v-sys.org

69.162.110.100 (US --> ARIN): www.limestonenetworks.com, an ISP,
  AbuseAdress: abuseteam at limestonenetworks.com and abuse at lstn.net
  This ISP seems to be well known for doing nothing against such attacks either
  carried out by its own staff or by its clients as can be seen in the postings
  of admins of other attacked systems:
   http://www.webhostingstuff.com/review/LimestoneNetworks.html
   http://www.webhostingtalk.com/showthread.php?t=1159070
   http://www.webhostingtalk.com/showthread.php?t=1183580


Anybody else get attacked by the above systems?
What else can be done in such a case?
Is this a case for CERT's ? Anybody have experience with CERT's and can give tips?



The attacks look like the following excerpts from the DNS log (before blocking them in the firewall):

# Log evidence:
#
# AR BC=BC48b Logfile=/var/log/named/named_misc.log GenTime=20120925-095445 ToAbuseEMA: support at v-sys.org
# AttackerIP=91.235.143.158 Hostname(rDNS)= IPfromHN(DNS)=
#   cAT=14869 cAS=7 cAR=4 CC=UA RIR=RIPE ASN=AS6849 JSC UKRTELECOM,
# AttackedServerIP(s)=82.211.8.197 84.200.248.120 84.201.4.43 84.200.248.111 84.200.20.194 84.200.43.148
# LogExcerpt (timezone: UTC+02 = GMT+02, syncd via NTP):

2012-09-22 16:06:52.905 security: info: client 91.235.143.158#80: query (cache) 'isc.org/ANY/IN' denied
2012-09-22 16:06:52.934 security: info: client 91.235.143.158#80: query (cache) 'isc.org/ANY/IN' denied
2012-09-22 16:06:52.956 security: info: client 91.235.143.158#80: query (cache) 'isc.org/ANY/IN' denied
2012-09-25 09:46:08.661 security: info: client 91.235.143.158#8775: query (cache) 'google.com/A/IN' denied
2012-09-25 09:46:08.663 security: info: client 91.235.143.158#52882: query (cache) 'google.com/A/IN' denied
2012-09-25 09:46:08.754 security: info: client 91.235.143.158#31714: query (cache) 'google.com/A/IN' denied
2012-09-25 09:46:08.794 security: info: client 91.235.143.158#7089: query (cache) 'google.com/A/IN' denied
2012-09-25 09:46:08.827 security: info: client 91.235.143.158#7064: query (cache) 'google.com/A/IN' denied
2012-09-25 09:46:08.833 security: info: client 91.235.143.158#16716: query (cache) 'google.com/A/IN' denied
2012-09-25 09:46:08.868 security: info: client 91.235.143.158#80: query (cache) 'isc.org/ANY/IN' denied


# Log evidence:
#
# AR BC=BC48b Logfile=/var/log/named/named_misc.log GenTime=20120923-022150 ToAbuseEMA: 
abuse at limestonenetworks.com
# AttackerIP=69.162.110.100 Hostname(rDNS)=100-110-162-69.static.reverse.lstn.net
#   cAT=2324432 cAS=300 cAR=10 CC=US RIR=ARIN ASN=AS46475 Limestone Networks, Inc.
# AttackedServerIP(s)=82.211.8.197 84.200.248.120 84.201.4.43 84.200.248.111 84.200.20.194 84.200.43.148
# LogExcerpt (timezone: UTC+02 = GMT+02, syncd via NTP):

2012-09-22 16:25:36.969 security: info: client 69.162.110.100#53: query (cache) 'ripe.net/ANY/IN' denied
2012-09-22 16:25:36.969 security: info: client 69.162.110.100#53: query (cache) 'ripe.net/ANY/IN' denied
2012-09-22 16:25:37.144 security: info: client 69.162.110.100#53: query (cache) 'ripe.net/ANY/IN' denied
2012-09-22 16:25:37.144 security: info: client 69.162.110.100#53: query (cache) 'ripe.net/ANY/IN' denied
2012-09-22 16:25:37.144 security: info: client 69.162.110.100#53: query (cache) 'ripe.net/ANY/IN' denied
2012-09-22 16:25:37.144 security: info: client 69.162.110.100#53: query (cache) 'ripe.net/ANY/IN' denied
2012-09-22 16:25:37.144 security: info: client 69.162.110.100#53: query (cache) 'ripe.net/ANY/IN' denied
2012-09-22 16:25:37.322 security: info: client 69.162.110.100#53: query (cache) 'ripe.net/ANY/IN' denied
2012-09-22 16:25:37.322 security: info: client 69.162.110.100#53: query (cache) 'ripe.net/ANY/IN' denied
2012-09-22 16:25:37.322 security: info: client 69.162.110.100#53: query (cache) 'ripe.net/ANY/IN' denied
2012-09-22 16:25:37.322 security: info: client 69.162.110.100#53: query (cache) 'ripe.net/ANY/IN' denied
2012-09-22 16:25:37.322 security: info: client 69.162.110.100#53: query (cache) 'ripe.net/ANY/IN' denied