topic Re: Local DNS Cannot resolve Internet-host in Network Security

Local DNS Cannot resolve Internet-host

Amin Shaikh — Mon, 11 Mar 2019 16:27:02 GMT

Hi,

I have local DNS Server and needs to resolve internet address on behalf of local users.

what steps are needed on Firewall.

LAN users points to local DNS Server for name-resolving

On ASA I have static NAT for local DNS Server with Public IP and

on Inside ACL I allowed udp port 53, on Outside ACL also allowed udp port 53.

It doesnt seems to work, AM I missing some config still

Re: Local DNS Cannot resolve Internet-host

Collin Clark — Fri, 16 Oct 2009 19:42:09 GMT

You don't need the static NAT (unless internet people contact this server for resolving your domain) and the outside ACL permitting UDP/53. Check your log when you do a DNS query and see if there is anything in there (post it if you like). Also x2 the ACL applied on the inside interface or post it if you have any doubts. Finally check the DNS inspection. The default is 512 which can be too small. Increase it to something like 1024.

policy-map type inspect dns preset_dns_map

parameters

message-length maximum 1024

Hope this helps.

Re: Local DNS Cannot resolve Internet-host

Amin Shaikh — Fri, 16 Oct 2009 20:09:25 GMT

Hi,

I have attached the ASA config.

DNS ServerIP:192.168.1.222.

From ASA I am able to ping DNS SERVER

and vice-versa.

We dont want LANusers to access internet using this link, so we have ACL on INSIDE.

I do have SMTP traffic from inside to outside and vice-versa working OK.

What is the command to apply name-server on ASA, so i can test name-resolution on ASA.(only for troubleshooting)

Re: Local DNS Cannot resolve Internet-host

Collin Clark — Fri, 16 Oct 2009 20:16:22 GMT

One thing I noticed is your outgoing NAT-

nat (INSIDE) 2 192.168.1.100 255.255.255.255

This only allows 1 host to NAT, 192.168.1.100. Your DNS server should be added, so it can NAT.

nat (INSIDE) 2 192.168.1.222 255.255.255.255

Re: Local DNS Cannot resolve Internet-host

Amin Shaikh — Sat, 17 Oct 2009 08:27:45 GMT

After addding it works. With NAT everthing is allowed from this host

How can I restrict this statement

nat (INSIDE) 2 192.168.1.222 255.255.255.255

for DNS query only and need to restrict with bandwidth for 256K.

Can this be done.

Re: Local DNS Cannot resolve Internet-host

Collin Clark — Mon, 19 Oct 2009 12:18:28 GMT

I don't have a way to test, but I think this will work to restrict the NAT to just DNS.

access-list dns-nat extended permit udp host 192.168.1.222 any eq domain

nat (inside) 2 access-list dns-nat

Here's a link for configuring QoS on the ASA.

http://www.cisco.com/en/US/products/hw/vpndevc/ps2030/products_tech_note09186a008084de0c.shtml