Cisco Site to Site VPN - DNS

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 - 192.168.1.1
Small Business Server 2011 (DHCP, DNS) - 192.168.1.2
4 Workstations

Office B:
Cisco 887 (DHCP, DNS) - 192.168.21.1
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 192.168.21.1 192.168.21.10
!
ip dhcp pool LAN_POOL
 import all
 network 192.168.21.0 255.255.255.0
 domain-name domain.local
 dns-server 192.168.1.2 192.168.21.1
 default-router 192.168.21.1
 netbios-name-server 192.168.1.2
!
!
ip domain name domain.local
ip name-server 123.456.798.1
ip name-server 123.456.789.2
ip cef
no ipv6 cef
!

Select allOpen 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