My bible is here: http://technet.microsoft.com/en-us/library/cc782417%28v=WS.10%29.aspx#w2k3tr_dfs_how_gndl

DFS is a complex service that involves many processes and interactions between clients, root servers, and domain controllers.

When a DFS client accesses a namespace, the client always chooses the first target in the target list in the referral. If the first target is available, a session setup is performed and client credentials are passed to the server, unless a prior connection already exists with the selected target. If the selected target cannot be accessed, the client attempts to access the next target in the list, and so on, until all targets are exhausted. If all targets are unavailable, then the client cannot access that portion of the DFS namespace.

Netbios protocol is used \\domaindfsroot\rootname   (but it possible to use DNS only) : WINS is the best option

Domain controllers (hosting the domain-based DFS) must be reachable using RPC

dfsutil /root:\\<Domain>\<Namespace Root> /view >.\dfsutil_view.txt

dfsdiag /testdcs >.\dfsdiag_testdcs.txt

dfsdiag /testreferral /dfspath:\\<Domain>\<Namespace Root> /full >.\dfsdiag_testreferral.txt

dfsdiag.exe /testdfsintegrity /dfsroot:\\<Domain>\<Namespace Root> /recurse /full >.\dfsdiag_testdfsintegrity.txt

Ports required:

Service Name Relevant Computers UDP TCP
NetBIOS Name Service Domain controllers; root servers that are not domain controllers; servers acting as link targets; client computers acting as link targets 137 137
NetBIOS Datagram Service Domain controllers; root servers that are not domain controllers; servers acting as link targets; client computers acting as link targets 138
NetBIOS Session Service Domain controllers; root servers that are not domain controllers; servers acting as link targets; client computers acting as link targets 139
LDAP Server Domain controllers 389 389
Remote Procedure Call (RPC) endpoint mapper Domain controllers 135
Server Message Block (SMB) Domain controllers; root servers that are not domain controllers; servers acting as link targets; client computers acting as link targets 445 445

 Network Capture of a Client Accessing a Domain-based Namespace reveals the following main steps:

The client connects to IPC$ on DC-01.

The client requests a root referral for the \\Contoso.com\Public namespace.

The domain controller provides a root referral that contains three root servers, \\Root-DFS-03\Public, \\Root-DFS-02\Public, and \Root-DFS-01\Public.

The client establishes a connection with the first root server in the referral, Root-DFS-03.

The client navigates to the Software link folder on the root server.

The root server responds with the STATUS_PATH_NOT_COVERED message, which indicates that this is a link folder and that the client must request a link referral.

The client connects to IPC$ on the root server.

The client requests a link referral to the Software link.

The root server sends a link referral that contains three link targets for the Software link: \\Noam-FS-1\Apps, \\Noam-FS-3\Apps, and \\Noam-FS-2\Apps.
The DFS client sets up a session with the first link target in the referral, \\Noam-FS-1\Apps.