Command Reference Guide

3Com Router 3000 Ethernet Family
Command Reference Guide Chapter 11 NAT Configuration Commands
3Com Corporation
11-6
[Router] nat alg ftp
11.1.6 nat dns-map
Syntax
nat dns-map domain-name global-addr global-port [ tcp | udp ]
undo nat dns-map domain-name
View
System view
Parameter
domain-name: Valid domain name that can be correctly translated by external DNS
servers.
global-addr: Public IP address that outside hosts can access.
global-port: Service port number that outside hosts can access.
tcp: Sets the transport protocol to TCP.
udp: Sets the transport protocol to UDP.
Description
Use the nat dns-map command to configure a NAT entry, mapping a domain name to a
triplet of external IP address, port number, and protocol type.
Use the undo nat dns-map command to remove the NAT entry for a domain name.
You may configure your internal hosts to access internal servers by domain name. In
case your intranet has no DNS server, an external DNS server will be involved to
provide domain name resolution service.
When an internal host attempts to access an internal server by domain name, its DNS
request is first forwarded to an external DNS server where the domain name is
resolved to a public IP address. The NAT server, however, could not identify the desired
internal server with this public IP address only. To allow it to correctly identify an internal
server by domain name, you must create a NAT entry for the domain name of the
internal server. This entry must include a service port number in addition to the public IP
address.
By default, no map entry exists for any domain name.
You may create up to 16 NAT entries for domain names.
Example
# Map a domain name to a triplet of public IP address, port number, and protocol type.
[Router] nat dns-map www.abc.com 202.112.0.1 80 tcp