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DNS Server Settings Overwritten by DHCP Connection (DHCP Relay Environment)

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Article ID: KB6624 KB Last Updated: 30 Aug 2010Version: 4.0
Summary:
DNS Server Settings Overwritten by DHCP Connection (DHCP Relay Environment)
Symptoms:
Environment:
  • NetScreen firewall is configured as a DHCP Relay
  • Remote NetScreen firewall is configured as a DHCP server
  • Centralized DHCP Management over VPN Connection
  • PC behind NetScreen obtains DHCP IP address from the Remote NetScreen firewall thru DHCP Relay
  • NetScreen firewall obtains untrust IP address from Internet Service Provider (ISP) via Point to Point Protocol over Ethernet (PPPoE)
  • NetScreen configured as a DNS server
Symptoms & Errors:
  • DNS server options get overwritten by PPPoE server on untrust side
  • PPPoE overwrites internal DNS settings
  • Don't want to use DNS the ISP provides
  • Use split DNS for private and public networks
  • set PPPoE DHCP-nochange does not work
Solution:

THIS SOLUTION APPLIES TO ALL NetScreen PRODUCT SUPPORT PPPoE CONNECTION.

Use of "set PPPoE DHCP-nochange" command to retain the internal DNS Server settings on the NetScreen applies to DHCP Server Environment ONLY.

By design, for NetScreen Device configured as a DHCP relay agent, the DNS Server settings will be overwritten by the PPPoE Connection. There is no way currently to prevent DNS settings from being overwritten if the DHCP clients obtain their addresses from the NetScreen via DHCP Relay.

To implement "set PPPoE DHCP-nochange" on Netscreen as DHCP Server, please refer to KB5240


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