Why are my servers showing up as the internal address?
by admin on Jan.09, 2007, under DNS, Networking, Routers
When you add a static nat in your Cisco router for one of your servers the router then knows the internal and external IP. When you do a DNS query on that server to an outside DNS server the router will translate your returned address to the internal IP for you. See below for the official explanation:
Q. Does Cisco IOS NAT support DNS queries?
A. Yes, Cisco IOS NAT does translate the address(es) which appear in DNS responses to name lookups (A queries) and inverse lookups (PTR queries). If an outside host sends a name-lookup to a DNS server on the inside, and that server responds with a local address, the NAT code translates that local address to a global address. The opposite is also true, and is how Cisco supports IP addresses that overlap. An inside host queries an outside DNS server, the response contains an address that matches the ACL specified on the outside source command, and the code translates the outside global address to an outside local address.
Time-to-live (TTL) values on all DNS resource records (RRs) which receive address translations in RR payloads are automatically set to zero.
Cisco IOS NAT does not translate IP addresses embedded in DNS zone transfers.
