Cisco ASA URL Filtering via DNS Inspection Policy Map

One of our Ipoque DPI appliance suddenly failed but activated its fail-to-wire feature. I had to temporarily perform URL filtering on the ASA 5525-X by creating regular expression (regex) for the domains to be blocked and apply a DNS inspection policy to block DNS lookups. For this example, I want to block domains such as Youtube, Facebook and Piratebay.

regex Youtube "youtube\.com"
regex Facebook "facebook\.com"
regex Piratebay "piratebay\.org"

class-map type regex match-any DomainBlockList
 match regex Youtube
 match regex Facebook
 match regex Piratebay

policy-map type inspect dns PM-DNS-inspect
  match domain-name regex class DomainBlockList
  drop-connection log   // DROP SPECIFIED DOMAINS AND ALLOW EVERYTHING ELSE

policy-map global_policy
 class inspection_default
  no inspect dns preset_dns_map   // REMOVE DEFAULT DNS INSPECTION POLICY
  inspect dns PM-DNS-inspect


I've also enabled syslog to verify if the regex and DNS filtering policy are working.

logging enable 
logging buffered informational
logging timestamp

ciscoasa# show log
Syslog logging: enabled
    Facility: 20
    Timestamp logging: enabled
    Standby logging: disabled
    Debug-trace logging: disabled
    Console logging: disabled
    Monitor logging: disabled
    Buffer logging: level informational, 1948 messages logged
    Trap logging: disabled
    Permit-hostdown logging: disabled
    History logging: disabled
    Device ID: disabled
    Mail logging: disabled
    ASDM logging: disabled
 inside:192.168.1.10/53050 (172.27.25.254/14713)
May 23 2016 17:09:30: %ASA-4-410003: DNS Classification: Dropped DNS request (id 7944) from inside:192.168.1.10/53050 to outside:8.8.8.8/53; matched Class 22: match domain-name regex class DomainBlockList
May 23 2016 17:09:30: %ASA-4-507003: udp flow from inside:192.168.1.10/53050 to outside:8.8.8.8/53 terminated by inspection engine, reason - inspector disconnected, dropped packet.
May 23 2016 17:09:30: %ASA-6-302016: Teardown UDP connection 511 for outside:8.8.8.8/53 to inside:192.168.1.10/53050 duration 0:00:00 bytes 0
May 23 2016 17:09:33: %ASA-6-302014: Teardown TCP connection 495 for outside:172.20.80.21/9100 to inside:192.168.1.10/50128 duration 0:00:30 bytes 0 SYN Timeout
May 23 2016 17:09:34: %ASA-6-305011: Built dynamic TCP translation from inside:192.168.1.10/50132 to outside:172.27.25.254/13351
May 23 2016 17:09:34: %ASA-6-302013: Built outbound TCP connection 512 for outside:172.20.80.21/9100 (172.20.80.21/9100) to inside:192.168.1.10/50132 (172.27.25.254/13351)
May 23 2016 17:09:34: %ASA-6-302015: Built outbound UDP connection 513 for outside:8.8.8.8/53 (8.8.8.8/53) to inside:192.168.1.10/53050 (172.27.25.254/14713)
May 23 2016 17:09:34: %ASA-4-410003: DNS Classification: Dropped DNS request (id 7944) from inside:192.168.1.10/53050 to outside:8.8.8.8/53; matched Class 22: match domain-name regex class DomainBlockList
May 23 2016 17:09:34: %ASA-4-507003: udp flow from inside:192.168.1.10/53050 to outside:8.8.8.8/53 terminated by inspection engine, reason - inspector disconnected, dropped packet.
May 23 2016 17:09:34: %ASA-6-302016: Teardown UDP connection 513 for outside:8.8.8.8/53 to inside:192.168.1.10/53050 duration 0:00:00 bytes 0
May 23 2016 17:09:35: %ASA-6-305011: Built dynamic UDP translation from inside:192.168.1.10/53051 to outside:172.27.25.254/9577
May 23 2016 17:09:35: %ASA-6-302015: Built outbound UDP connection 514 for outside:8.8.8.8/53 (8.8.8.8/53) to inside:192.168.1.10/53051 (172.27.25.254/9577)
May 23 2016 17:09:35: %ASA-6-305011: Built dynamic UDP translation from inside:192.168.1.10/53052 to outside:172.27.25.254/38752
May 23 2016 17:09:35: %ASA-6-302015: Built outbound UDP connection 515 for outside:8.8.8.8/53 (8.8.8.8/53) to inside:192.168.1.10/53052 (172.27.25.254/38752)
May 23 2016 17:09:35: %ASA-6-302016: Teardown UDP connection 515 for outside:8.8.8.8/53 to inside:192.168.1.10/53052 duration 0:00:00 bytes 72
May 23 2016 17:09:35: %ASA-6-302016: Teardown UDP connection 514 for outside:8.8.8.8/53 to inside:192.168.1.10/53051 duration 0:00:00 bytes 72
May 23 2016 17:09:37: %ASA-6-305012: Teardown dynamic TCP translation from inside:192.168.1.10/50127 to outside:172.27.25.254/39345 duration 0:01:00
May 23 2016 17:09:40: %ASA-6-305012: Teardown dynamic UDP translation from inside:192.168.1.10/52130 to outside:172.27.25.254/50331 duration 0:00:30
May 23 2016 17:09:40: %ASA-6-302014: Teardown TCP connection 497 for outside:216.146.46.10/445 to inside:192.168.1.10/50129 duration 0:00:30 bytes 0 SYN Timeout
May 23 2016 17:09:41: %ASA-6-302014: Teardown TCP connection 498 for outside:216.146.46.11/445 to inside:192.168.1.10/50130 duration 0:00:30 bytes 0 SYN Timeout
May 23 2016 17:09:43: %ASA-6-305012: Teardown dynamic UDP translation from inside:192.168.1.10/60600 to outside:172.27.25.254/9592 duration 0:00:30
May 23 2016 17:09:43: %ASA-6-305012: Teardown dynamic ICMP translation from inside:192.168.1.10/1 to outside:172.27.25.254/44940 duration 0:00:30
May 23 2016 17:09:50: %ASA-6-305012: Teardown dynamic UDP translation from inside:192.168.1.10/52188 to outside:172.27.25.254/40294 duration 0:00:30
May 23 2016 17:09:56: %ASA-6-305012: Teardown dynamic UDP translation from inside:192.168.1.10/53050 to outside:172.27.25.254/14713 duration 0:00:30
May 23 2016 17:10:00: %ASA-6-305011: Built dynamic TCP translation from inside:192.168.1.10/50133 to outside:172.27.25.254/40275
May 23 2016 17:10:00: %ASA-6-302013: Built outbound TCP connection 516 for outside:172.20.80.21/9100 (172.20.80.21/9100) to inside:192.168.1.10/50133 (172.27.25.254/40275)


Below is the full config that was applied on my lab ASA 5505 running version 8.3.

ciscoasa# show run
: Saved
:
ASA Version 8.3(2)
!
hostname ciscoasa
enable password 8Ry2YjIyt7RRXU24 encrypted
passwd 2KFQnbNIdI.2KYOU encrypted
names
!
interface Vlan1
 nameif inside
 security-level 100
 ip address 192.168.1.254 255.255.255.0
!
interface Vlan2
 nameif outside
 security-level 0
 ip address 172.27.25.254 255.255.255.0
!
interface Ethernet0/0
 switchport access vlan 2
!
interface Ethernet0/1
!
interface Ethernet0/2
 shutdown
!
interface Ethernet0/3
 shutdown
!
interface Ethernet0/4
 shutdown
!
interface Ethernet0/5
 shutdown
!
interface Ethernet0/6
 shutdown
!
interface Ethernet0/7
 shutdown
!
regex Piratebay "piratebay\.org"
regex Youtube "youtube\.com"
regex Facebook "facebook\.com"
boot system disk0:/asa832-k8.bin
ftp mode passive
object network INSIDE-PAT
 subnet 192.168.1.0 255.255.255.0
pager lines 24
logging enable
logging timestamp
logging buffered informational
mtu inside 1500
mtu outside 1500
icmp unreachable rate-limit 1 burst-size 1
no asdm history enable
arp timeout 14400
!
object network INSIDE-PAT
 nat (inside,outside) dynamic interface
route outside 0.0.0.0 0.0.0.0 172.27.25.1 1
timeout xlate 3:00:00
timeout conn 1:00:00 half-closed 0:10:00 udp 0:02:00 icmp 0:00:02
timeout sunrpc 0:10:00 h323 0:05:00 h225 1:00:00 mgcp 0:05:00 mgcp-pat 0:05:00
timeout sip 0:30:00 sip_media 0:02:00 sip-invite 0:03:00 sip-disconnect 0:02:00
timeout sip-provisional-media 0:02:00 uauth 0:05:00 absolute
timeout tcp-proxy-reassembly 0:01:00
dynamic-access-policy-record DfltAccessPolicy
no snmp-server location
no snmp-server contact
snmp-server enable traps snmp authentication linkup linkdown coldstart
crypto ipsec security-association lifetime seconds 28800
crypto ipsec security-association lifetime kilobytes 4608000
telnet timeout 5
ssh timeout 5
console timeout 0

threat-detection basic-threat
threat-detection statistics access-list
no threat-detection statistics tcp-intercept
!
class-map type regex match-any DomainBlockList
 match regex Youtube
 match regex Facebook
 match regex Piratebay
class-map inspection_default
 match default-inspection-traffic
!
!
policy-map type inspect dns preset_dns_map
 parameters
  message-length maximum client auto
  message-length maximum 512
policy-map type inspect dns PM-DNS-inspect
 parameters
 match domain-name regex class DomainBlockList
  drop-connection log
policy-map global_policy
 class inspection_default
  inspect ftp
  inspect h323 h225
  inspect h323 ras
  inspect ip-options
  inspect netbios
  inspect rsh
  inspect rtsp
  inspect skinny
  inspect esmtp
  inspect sqlnet
  inspect sunrpc
  inspect tftp
  inspect sip
  inspect xdmcp
  inspect dns PM-DNS-inspect
!
service-policy global_policy global
prompt hostname context
call-home
 profile CiscoTAC-1
  no active
  destination address http https://tools.cisco.com/its/service/oddce/services/DDCEService
  destination address email callhome@cisco.com
  destination transport-method http
  subscribe-to-alert-group diagnostic
  subscribe-to-alert-group environment
  subscribe-to-alert-group inventory periodic monthly
  subscribe-to-alert-group configuration periodic monthly
  subscribe-to-alert-group telemetry periodic daily
Cryptochecksum:84d1dbdacf047ec442ba73e29b20eecd
: end