Cisco Site to Site VPN - DNS

Posted on 2012-09-21
Last Modified: 2012-09-24
Hi guys,

I've got a query to do with DNS and Site to Site VPN involving a Cisco 877 and 887.

Here is a quick and basic rundown of the two sites:

Office A: - Main office
Cisco 877 -
Small Business Server 2011 (DHCP, DNS) -
4 Workstations

Office B:
Cisco 887 (DHCP, DNS) -
2 Workstations

The router at Office A has been in place for a couple of years now and running fine, the Small Business Server is doing all the usuals, DHCP & DNS etc...

The Cisco VPN Client & Windows VPN weren't ideal so we have decided to go for a permenant tunnel between both offices.

Today I configured the Cisco 887 at Office B, the VPN connection is up and running.

What I was hoping you guys could help me with is the DHCP & DNS for Office B.
Currently it is setup as following...

ip dhcp excluded-address
ip dhcp pool LAN_POOL
 import all
 domain-name domain.local
ip domain name domain.local
ip name-server 123.456.798.1
ip name-server 123.456.789.2
ip cef
no ipv6 cef

Open in new window

I want to make sure that a workstation at Office B looks directly out of the network for internet and only looks up the tunnel for devices and services in Office A. I understand the NAT governs this so should be fine? I'm slightly concerned that if the broadband was to go down at Office A that Office B will be without DNS...

I hope I'm being clear, and if you guys need any more of my config I'm happy to paste it in.

Many thanks in advance
Question by:systemagic
    LVL 35

    Accepted Solution

    Looking at: dns-server, the clients get two DNS servers. The first at office A ( and the second is local at office b (
    So Office B won't be without DNS when A goes down. There will be some delay because the clients will first try to query the DNS server at office A before trying the local DNS server.

    You could set the local DNS server first and have a look at conditional DNS forwarding on the server .
    LVL 1

    Author Closing Comment

    Thank you, this answers my question :)
    Will do some testing.

    LVL 35

    Expert Comment

    by:Ernie Beek
    My pleasure :)

    Thx 4 the points.

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