NAT Server for external-to-internal access through domain name configuration example

As shown in Figure 60, Web server at 10.110.10.2/24 in the internal network provides services for external users. A DNS server at 10.110.10.3/24 is used to resolve the domain name of the Web server. The company has two public IP addresses: 202.38.1.2 and 202.38.1.3.

Configure NAT Server to allow external users to access the internal Web server by using the domain name.

To meet the network requirements, you must perform the following tasks:

• Configure NAT Server to map the private IP address and port of the DNS server to a public address and port. NAT Server allows the external host to access the internal DNS server for domain name resolution.

• Enable ALG for DNS and configure outbound dynamic NAT to translate the private IP address of the Web server in the payload of the DNS response packet into a public IP address.

# Specify IP addresses for the interfaces on the router. (Details not shown.)

# Enable NAT with ALG for DNS.

<Router> system-view
[Router] nat alg dns

# Configure ACL 2000, and create a rule to permit packets only from 10.110.10.2 to pass through.

[Router] acl basic 2000
[Router-acl-ipv4-basic-2000] rule permit source 10.110.10.2 0
[Router-acl-ipv4-basic-2000] quit

# Create address group 1.

[Router] nat address-group 1

# Add address 202.38.1.3 to the group.

[Router-address-group-1] address 202.38.1.3 202.38.1.3
[Router-address-group-1] quit

# Configure NAT Server on interface GigabitEthernet 1/0/2 to map the address 202.38.1.1 to 10.110.10.3. External users can access the internal DNS server.

[Router] interface gigabitethernet 1/0/2
[Router-GigabitEthernet1/0/2] nat server protocol udp global 202.38.1.2 inside 10.110.10.3 dns

# Enable outbound NO-PAT on interface GigabitEthernet 1/0/2. Use the address in address group 1 to translate the private address in DNS response payload, and allow reversible NAT.

[Router-GigabitEthernet1/0/2] nat outbound 2000 address-group 1 no-pat reversible

# Verify that the host on the external network can access the internal Web server by using the server's domain name. (Details not shown.)

# Display all NAT configuration and statistics.

[Router] display nat all
NAT address group information:
  Totally 1 NAT address groups.
  Address group 1:
    Port range: 1-65535
    Address information:
      Start address         End address
      202.38.1.3            202.38.1.3

NAT outbound information:
  Totally 1 NAT outbound rules.
  Interface: GigabitEthernet1/0/2
    ACL: 2000
    Address group ID: 1
    Port-preserved: N    NO-PAT: Y         Reversible: Y
    Config status: Active

NAT internal server information:
  Totally 1 internal servers.
  Interface: GigabitEthernet1/0/2
    Protocol: 17(UDP)
    Global IP/port: 202.38.1.2/53
    Local IP/port : 10.110.10.3/53
    Config status : Active

NAT logging:
  Log enable          : Disabled
  Flow-begin          : Disabled
  Flow-end            : Disabled
  Flow-active         : Disabled
  Port-block-assign   : Disabled
  Port-block-withdraw : Disabled
  Alarm               : Disabled

NAT mapping behavior:
  Mapping mode : Address and Port-Dependent
  ACL          : ---
  Config status: Active

NAT ALG:
  DNS        : Enabled
  FTP        : Enabled
  H323       : Enabled
  ICMP-ERROR : Enabled
  ILS        : Enabled
  MGCP       : Enabled
  NBT        : Enabled
  PPTP       : Enabled
  RSH        : Enabled
  RTSP       : Enabled
  SCCP       : Enabled
  SIP        : Enabled
  SQLNET     : Enabled
  TFTP       : Enabled
  XDMCP      : Enabled

# Display NAT session information generated when Host accesses Web server.

[Router] display nat session verbose
Initiator:
  Source      IP/port: 202.1.1.2/1694
  Destination IP/port: 202.38.1.3/8080
  DS-Lite tunnel peer: -
  VPN instance/VLAN ID/Inline ID: -/-/-
  Protocol: TCP(6)
  Inbound interface: GigabitEthernet1/0/2
Responder:
  Source      IP/port: 10.110.10.2/8080
  Destination IP/port: 202.1.1.2/1694
  DS-Lite tunnel peer: -
  VPN instance/VLAN ID/Inline ID: -/-/-
  Protocol: TCP(6)
  Inbound interface: GigabitEthernet1/0/1
State: TCP_ESTABLISHED
Application: HTTP
Start time: 2012-08-15 14:53:29  TTL: 3597s
Initiator->Responder:            7 packets        308 bytes
Responder->Initiator:            5 packets        312 bytes

Total sessions found: 1