deny dns traffic to the Internet except to specific ips

[symhelp]

Is there a way to restrict users from being able to use other dns servers other then the one the receive thru dhcp via an asa5505? I'm using a dns filter website and want to force people to use these dns servers. There isn't any domain controllers on this network so i can't restrict changes being make or limit their access. these would be people using there personal computers on this network.
thanks in advanced!

 

[North323]

you can add the specific dns servers in your config. post a scrubbed config

 

[Supergrrover]

Access-list inside-out permit udp any host [dns server ip] eq dns
Access-list inside-out deny udp any any eq dns
Access-list inside-out permit ip any any

access-group inside-out in interface inside

Brent
Systems Engineer / Consultant
CCNP, CCSP

 

[symhelp]

supergrrover - i added these lines and was still about to access the internet by manually adding the dns servers to my pc. i want to restrict this so that they are forced to use dhcp and us the dns servers we are assigning the.

thanks in advanced for your help


here is the config:

ASA Version 7.2(4)
!
hostname externalciscoasa
domain-name opendns
enable password encrypted
passwd encrypted
names
!
interface Vlan1
nameif inside
security-level 100
ip address 192.168.10.1 255.255.255.0
!
interface Vlan2
nameif outside
security-level 0
ip address xxx.xxx.xxx.xxx xxx.xxx.xxx.xxx
!
interface Vlan3
no forward interface Vlan1
nameif dmz
security-level 50
ip address dhcp
!
interface Ethernet0/0
switchport access vlan 2
!
interface Ethernet0/1
!
interface Ethernet0/2
!
interface Ethernet0/3
!
interface Ethernet0/4
!
interface Ethernet0/5
!
interface Ethernet0/6
!
interface Ethernet0/7
!
ftp mode passive
clock timezone EST -5
clock summer-time EDT recurring
dns domain-lookup inside
dns server-group DefaultDNS
name-server 208.67.222.222
name-server 208.67.220.220
domain-name opendns
same-security-traffic permit intra-interface
access-list inside-out extended permit udp any host 208.67.222.222 eq dnsix
access-list inside-out extended deny udp any any eq dnsix
access-list inside-out extended permit ip any any
access-list inside_nat0_outbound extended permit ip any 172.16.1.0 255.255.255.0

access-list psoexternal_splitTunnelAcl standard permit 192.168.10.0 255.255.255.
0
pager lines 24
logging enable
logging asdm informational
mtu inside 1500
mtu outside 1500
mtu dmz 1500
ip local pool vpnpool 172.16.1.100-172.16.1.199 mask 255.255.255.0
icmp unreachable rate-limit 1 burst-size 1
asdm image disk0:/asdm-524.bin
no asdm history enable
arp timeout 14400
global (outside) 101 interface
nat (inside) 0 access-list inside_nat0_outbound
nat (inside) 101 192.168.10.0 255.255.255.0
access-group inside-out in interface inside
route outside 0.0.0.0 0.0.0.0 206.210.91.93 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
http server enable
http 192.168.1.0 255.255.255.0 inside
http 192.168.10.10 255.255.255.255 inside
no snmp-server location
no snmp-server contact
snmp-server enable traps snmp authentication linkup linkdown coldstart
crypto ipsec transform-set ESP-3DES-SHA esp-3des esp-sha-hmac
crypto dynamic-map inside_dyn_map 20 set pfs group1
crypto dynamic-map inside_dyn_map 20 set transform-set ESP-3DES-SHA
crypto dynamic-map inside_dyn_map 40 set pfs group1
crypto dynamic-map inside_dyn_map 40 set transform-set ESP-3DES-SHA
crypto dynamic-map inside_dyn_map 60 set pfs group1
crypto dynamic-map inside_dyn_map 60 set transform-set ESP-3DES-SHA
crypto dynamic-map outside_dyn_map 20 set pfs group1
crypto dynamic-map outside_dyn_map 20 set transform-set ESP-3DES-SHA
crypto dynamic-map outside_dyn_map 40 set pfs group1
crypto dynamic-map outside_dyn_map 40 set transform-set ESP-3DES-SHA
crypto map inside_map 65535 ipsec-isakmp dynamic inside_dyn_map
crypto map inside_map interface inside
crypto map outside_map 65535 ipsec-isakmp dynamic outside_dyn_map
crypto map outside_map interface outside
crypto isakmp enable inside
crypto isakmp enable outside
crypto isakmp policy 10
authentication pre-share
encryption 3des
hash sha
group 2
lifetime 86400
crypto isakmp nat-traversal 20
telnet 192.168.10.10 255.255.255.255 inside
telnet timeout 5
ssh timeout 5
console timeout 0
management-access inside
dhcpd auto_config outside
!
dhcpd address 192.168.10.20-192.168.10.200 inside
dhcpd dns 208.67.222.222 208.67.220.220 interface inside
dhcpd lease 86400 interface inside
dhcpd ping_timeout 750 interface inside
dhcpd enable inside
!

group-policy psoexternal internal
group-policy psoexternal attributes
vpn-tunnel-protocol IPSec
split-tunnel-policy tunnelspecified
split-tunnel-network-list value psoexternal_splitTunnelAcl
username administrator password AeeC9uWXZBBjE8Rg encrypted privilege 0
username administrator attributes
vpn-group-policy psoexternal
tunnel-group psoexternal type ipsec-ra
tunnel-group psoexternal general-attributes
address-pool vpnpool
default-group-policy psoexternal
tunnel-group psoexternal ipsec-attributes
pre-shared-key *
!
class-map inspection_default
match default-inspection-traffic
!
!
policy-map type inspect dns preset_dns_map
parameters
message-length maximum 512
policy-map global_policy
class inspection_default
inspect dns preset_dns_map
inspect ftp
inspect h323 h225
inspect h323 ras
inspect rsh
inspect rtsp
inspect esmtp
inspect sqlnet
inspect skinny
inspect sunrpc
inspect xdmcp
inspect sip
inspect netbios
inspect tftp
!
service-policy global_policy global
prompt hostname context
Cryptochecksum:
: end

 

[Supergrrover]

access-list inside-out extended permit udp any host 208.67.222.222 eq dnsix
should just be dns


Brent
Systems Engineer / Consultant
CCNP, CCSP

 

[symhelp]

it changed it automatically to dnsix, i didn't even realize that. dns is actually domain for us. so once i changed it to eq domain it works fine. thanks! one more question, is there anyway to disable the use of proxy servers on the asa?

thanks!

 

[Supergrrover]

Not really. Setup your own and make it the only ip to be allowed web traffic.

Brent
Systems Engineer / Consultant
CCNP, CCSP