ISA Server and Network Card Config

Inside NIC has its gateway set to 10.2.1.1, outside NIC gets whatever gateway you have on that subnet (presumably 10.2.1.1).

DNS for each NIC should also match whatever is appropriate for each segment (they can be different if that is how your network is set up).

ISA defines "internal" and "external" through its policy system. If you are setting up in cache mode, there's no real need for internal/external to be configured. If you're going down the path of an integrated mode ISA firewall, the configuration wizard will offer you a chance to specify which is which. Otherwise, you'll need to create the policies by hand.

Internal Subnet => ISA Internal(10.1.1.2) Ext(10.2.1.3) => Router(10.2.1.1) Ext(#.#.#.#)

You need to configure your External Nic GW as 10.2.1.1 and Internal Nic with No Gateway. Why. Because your internal Nic Card does not need a gateway to communicate with the Devices on its subnet and when you leave the gateway blank. All information coming from your Internal Network Will be sent to the gate way of your external Nic.

For DNS Resolution the DNS Server information should be on the client Machine typically the DNS Server is an External IP Address or if you have a Local DNS Server you should configure that server to Forward Request to a External DNS Server. As far as what you put on your ISA Server I recommend the following. Ifyou have a local DNS server Configure the Internal Nic with the IP Address of the Internal DNS Server and the External Nic with the IP Address of an External DNS Server.

ISA know which card is which by the configuration of your LAT (local AddressTable). The information in this table will tell ISA which IP?s or subnets are considered Local Address and the internal Nic card IP Address will fall in this rage of Address.

Short and simple,

Set the router IP(10.2.1.1) as the default for External(10.2.1.3) default gateway, and leave it blank for the internal card(10.1.1.2).

For the DNS part,

For external interface(10.2.1.3)
Set the Preferred DNS Server as theDNS IP address you get from your ISP.

For internal interface(10.1.1.2)
Set the DNS IP that you get from your ISP in the Preferred DNS Server, and the ISA Server internal IP(10.1.1.2) in the Alternate DNS Server.

Your ISA Server can indentifywhich is the internal and external cards based on the LAT(Local Address Table) that you construct when you install ISA.