I have a Cisco 1811 configured with PAT:
interface FastEthernet0 ip address dhcp ip nat outside interface Vlan1 ip address 192.168.0.1 255.255.255.0 ip nat inside ip nat inside source route-map primary interface FastEthernet0 overload route-map primary permit 10 match ip address 9 match interface FastEthernet0 access-list 9 permit 192.168.0.0 0.0.0.255 ip route 0.0.0.0 0.0.0.0 FastEthernet0 dhcp 99
I'm also using this router as a caching DNS relay:
ip dns server
Clients on VLAN1 could send DNS query's to 192.168.0.1 and the router would relay them to the DNS servers from the DHCP lease on Fas0.
However, recently my (residential) ISP began blocking inbound UDP port 53 (for good reason). This is posing a problem because the relayed packets from the Cisco router have SrcPort:53 and DestPort:53. The replies never make it back.
So my question is: Is there anyway to re-write all UDP packets output from Fas0 changing ScrPort 53 to some other fixed port, and then re-writing them back when they return. Or is there some way I could force them to send from the inside of the NAT and would that solve the problem?
All suggestions or ideas welcome.