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[SRX] How to propagate DNS information from ISP to the Client PC

  [KB31279] Show Article Properties


Summary:

This article describes how to propagate DNS information from DHCP in ISP to the Client PC in an internal network behind the SRX firewall.

Symptoms:

Customer has a DHCP server in ISP which provides IP address details to the PC behind the SRX. The topology is as given below.

Topology:
ISP(DHCP_SERVER)---20.1.1.0/24-----(ge-0/0/1)SRX(ge-0/0/2)----30.1.1.0/24------PC

This article provides details to configure and verify the settings to provide DNS details from DHCP server to the PC.
Solution:
The following setting example is for SRX345.

set version 15.1X49-D60.7
set system services dhcp pool 30.1.1.0/24 address-range low 30.1.1.2
set system services dhcp pool 30.1.1.0/24 address-range high 30.1.1.10
set system services dhcp pool 30.1.1.0/24 default-lease-time 1800
set system services dhcp pool 30.1.1.0/24 router 30.1.1.1
set system services dhcp pool 30.1.1.0/24 propagate-settings ge-0/0/1.0 
set security policies default-policy permit-all
set security zones security-zone untrust interfaces ge-0/0/1.0 host-inbound-traffic system-services all
set security zones security-zone trust interfaces irb.0 host-inbound-traffic system-services all
set interfaces ge-0/0/1 unit 0 family inet dhcp server-address 20.1.1.1
set interfaces ge-0/0/1 unit 0 family inet dhcp update-server
set interfaces ge-0/0/2 unit 0 family ethernet-switching vlan members 3
set interfaces irb unit 0 family inet address 30.1.1.1/24
set protocols l2-learning global-mode switching
set vlans vlan3 vlan-id 3
set vlans vlan3 l3-interface irb.0

Verification in SRX:
root@SRX-345-1# run show system services dhcp client ge-0/0/1.0

Logical Interface name ge-0/0/1.0
Hardware address 30:b6:4f:2d:7b:42
Client status bound
Server address 20.1.1.1
Address obtained 20.1.1.2
Update server enabled
Lease obtained at 2016-11-16 11:13:45 HKT
Lease expires at 2016-11-30 11:13:45 HKT

DHCP options:
Name: server-identifier, Value: 20.1.1.1
Code: 1, Type: ip-address, Value: 255.255.255.0
Name: router, Value: [ 20.1.1.1 ]
Name: name-server, Value: [ 8.8.8.8 ]  <--From the ISP
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