RE: IP Address Assignment for VPN clients.
- From: "William Holmes" <wtholmes@xxxxxxxxxxxxxx>
- To: "[ISAserver.org Discussion List]" <isalist@xxxxxxxxxxxxx>
- Date: Thu, 2 Dec 2004 16:18:05 -0500
Hello,
Unfortunately the DNS server that was originally being used is not offline.
It is just not cooperating. In this case (and more and more) the ISP does not
allow queries from outside its own subnets to use their DNS servers. The DNS
responds but does not return a query. So Windows keeps trying to use it. This
paralizes the client.
Now I could have my VPN clients use split Routing but that's not really
acceptable from a security standpoint. In addition it creates other problems
with routing due to IP restrictions on our subnets.
However all is not lost. Your explanation has gave me an idea. I thought if
I simply block all DNS access from my VPN clients to external DNS/Wins
servers that it would force them to behave in the manner you have explained.
In fact this solved the problem.
Bill
-----Original Message-----
From: Joe Pochedley [mailto:joepochedley@xxxxxxxxx]
Sent: Thursday, December 02, 2004 8:56 AM
To: [ISAserver.org Discussion List]
Subject: [isalist] RE: IP Address Assignment for VPN clients.
http://www.ISAserver.org
The Static pool clients will take the DNS and WINS settings from the RRAS
server itself.
Whatever DNS and WINS servers are configured on the RRAS server will be
passed to the clients. So long as this information is set up properly on the
RRAS server, I've never had an issue with the clients receiving it.
However... In either case, DHCP or Static Pool, if the VPN client already
has "local" DNS (or I suppose WINS, though I've never had an
issue with WINS) servers, those will not be "overridden"... By local
DNS I mean a DNS server on the same subnet as the client's Ethernet (802.11,
whatever) interface... This is usually only a problem with users who have
SOHO equipment on broadband connections (Microsoft, dLink, SMC, Netgear;
Linksys does NOT have this issue).
The reason for this issue is due to the way Windows handles DNS servers.
Contrary to popular belief, the DNS server listed as "primary" is not always
the first one contacted. The first DNS request issued will use the primary
dns server. If that server is offline then the next will be picked. Once a
working DNS server is found, Windows will use it to resolve all DNS requests
until it is no longer available. Even if a new DNS server is inserted higher
in the list, the old one will be used so long as it is available.
That means, so long as the DNS server the client was in contact with before
the VPN connection is established is available, that DNS server will remain
the first one contacted. If the DNS server is "local" than it is still
"available"... It's a bit more complex than this, but that's the gist of if
(I hope I explained it clear enough).
Users who use standard dial-up services and then connect to the VPN
afterwards typically don't experience these issues.
Hope that helps.
Joe Pochedley
A computer terminal is not some clunky old television with a typewriter in
front of it. It is an interface where the mind and body can connect with the
universe and move bits of it about. -Douglas Adams
-----Original Message-----
From: William Holmes [mailto:wtholmes@xxxxxxxxxxxxxx]
Sent: Wednesday, December 01, 2004 9:46 PM
To: [ISAserver.org Discussion List]
Subject: [isalist] RE: IP Address Assignment for VPN clients.
http://www.ISAserver.org
Hello,
I would like to use a real dhcp server so that the clients get configured
correctly. It has been my experience that when using the static pool other
dhcp options are not correctly configured. In particular dns and wins servers
do not get configured to override the dhcp and wins servers that were
configured prior to the VPN tunnel being setup.
Bill
-----Original Message-----
From: Joe Pochedley [mailto:joepochedley@xxxxxxxxx]
Sent: Wednesday, December 01, 2004 11:24 AM
To: [ISAserver.org Discussion List]
Subject: [isalist] RE: IP Address Assignment for VPN clients.
http://www.ISAserver.org
William,
If you want to use a separate address pool for the VPN connections, then why
don't you just set it up that way on the RRAS server? The "static pool"
essentially acts like DHCP just for the VPN/RRAS clients...
Why do you want to complicate it more than necessary?
Joe Pochedley
A computer terminal is not some clunky old television with a typewriter in
front of it. It is an interface where the mind and body can connect with the
universe and move bits of it about. -Douglas Adams
-----Original Message-----
From: William Holmes [mailto:wtholmes@xxxxxxxxxxxxxx]
Sent: Wednesday, December 01, 2004 9:48 AM
To: [ISAserver.org Discussion List]
Subject: [isalist] IP Address Assignment for VPN clients.
http://www.ISAserver.org
Hello,
When configuring a VPN server you are given two choices for address
assignment. The first is DHCP and the second is a static address pool.
When configured to use a static pool you can essentially assign any subnet to
the VPN network. However if you want to use DHCP you are required to choose
a network adapter from which to assign addresses.
If you choose to use the Internal Interface then your VPN clients will share
the address space of the internal network.
I would like to use DHCP for address assignement and still have the VPN
network setup in its own address space. However this does not seem to be
possible. If I enable the DHCP relay agent on the VPN server and point it at
my DHCP server there is no way to tell the VPN interface when you make your
request "use this subnet". Instead it will use the subnet associated with the
adapter chosen on the IP property page.
If I am reading this correctly: Choosing a specific adapter is the only way
to configure the TCP/IP paramters of the VPN pseudo interface. In otherwords
it is the only way to decide on which subnet VPN clients will use.
Is there another way? The only thing I can think to do is add another
network adapter to my server and use it as the configuration adapter.
However this complicates things quite a bit and will require changing my ISA
server's config quite a bit.
Is there a way to use DHCP and assing the IP subnet to a VPN interface
without using a "Real" Interface?
Thanks
Bill
William Holmes (MCP)
Department of Computer Science
310 Upson Hall
Cornell University
Ithaca, NY 14853
wtholmes@xxxxxxxxxxxxxx
607 255-1757 (o) 607 227-6049 (c)
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