RE: S2S VPN: why are static routes sometimes needed?
- From: "Roy Tsao" <roy_tsao@xxxxxxxxxxxx>
- To: isalist@xxxxxxxxxxxxx
- Date: Sun, 8 Jan 2006 06:12:11 -0700
Hi Stefaan,
Let us cencer on your initial diagrams you illustruated.
In case the S2S VPN is within the protected network of ISA, it would
be another story.
If your saying "The route decision should be made on the outer IP header"
is correct, why you need to addup a static route from ISA-A to internal
network ID of ISA-B, then why you ask for this question??
Thanks,
Roy Tsao
> Hi Roy,
>
> You wrote "ISA decides route before processing ESP". That would be a very
> stupid way of determining the route! The route decision should be made on
> the outer IP header (the tunnel) and not on the inner IP header (the
> encapsulated traffic). In my case the remote tunnel endpoint is on a direct
> connected network. So, the router RTR shouldn't be envolved at all.
>
> As an example, two more diagrams were a S2S VPN connection is needed through
> a partner connection:
>
> +--- [RT1] --- Internet
> LAN --- [ISA] ---+
> +--- [RT2] --- Partner Network
>
>
> LAN --- [ISA] --- [RT1] --- Internet
> !
> +------ [RT2] --- Partner Network
>
>
> Thanks,
> Stefaan
>
>
> -----Original Message-----
> From: Roy Tsao [mailto:roy_tsao@xxxxxxxxxxxx]
> Sent: zondag 8 januari 2006 9:24
> To: [ISAserver.org Discussion List]
> Subject: [isalist] RE: S2S VPN: why are static routes sometimes needed?
>
> http://www.ISAserver.org
>
>
> Hi Stefaan,
>
> After various lab test by me and also other ISA fans, we suspect in our
> environment, you can add up a static route from upstream router to ISA-B's
> external NIC. This is becuase
> - no route tale change at ISA after enable S2S IPsec Tunnel VPN
> - ISA decides route before processing ESP
> - ESP is sent based on fixed route when packet exit ISA.
> - when upstream router receive ESP heading for ISA-B's exernal NIC, it has
> no route information at all!
>
> To addup a static route at ISA-A to ISA-B's internal network ID is one of
> soultion based on above reason. However, is it more proper to set up adjust
> route setting at upstream route? or any reason like security concern is
> there making impossible?
>
> As for your 2nd test scenario, may I understand the failure is due to
> diabled packet relay at router side?
>
>
>
> > Hi Jim,
> >
> > OK, I took up the challenge and replaced ISA-B with a Windows 2003
> > RRAS server :-)
> >
> > With the help of
> > http://support.microsoft.com/default.aspx?scid=kb;en-us;816514 I
> > configured an IPSec tunnel to the ISA-A. Guess what... you are right!
> > I found exact the same behavior.
> >
> > I even simplified further the test environment as follows:
> >
> > 192.168.1.0/24
> > vvv
> > LAN-A -------- [ISA-A] ---+
> > 192.168.22.0/24 .10 !
> > +--- [RTR] --- Internet
> > ! .1
> > .30 !
> > LAN-B -------- [ISA-B] ---+
> > 192.168.44.0/24
> >
> >
> > On ISA-A:
> > ---------
> >
> > Remote Site Network contains:
> > - 192.168.1.30/32
> > - 192.168.44.0/24
> >
> > If Default gateway = 192.168.1.1 then the static route
> > '192.168.44.0/24 Gateway 192.168.1.30' is needed.
> > If Default gateway = 192.168.1.30 then no static routes are needed.
> >
> >
> > On ISA-B:
> > ---------
> >
> > Remote Site Network contains:
> > - 192.168.1.10/32
> > - 192.168.22.0/24
> >
> > If Default gateway = 192.168.1.1 then the static route
> > '192.168.22.0/24 Gateway 192.168.1.10' is needed.
> > If Default gateway = 192.168.1.10 then no static routes are needed.
> >
> >
> > Thanks,
> > Stefaan
> >
> > -----Original Message-----
> > From: Jim Harrison [mailto:Jim@xxxxxxxxxxxx]
> > Sent: dinsdag 27 december 2005 21:23
> > To: [ISAserver.org Discussion List]
> > Subject: [isalist] RE: S2S VPN: why are static routes sometimes needed?
> >
> > http://www.ISAserver.org
> >
> > That is odd, but I'll bet you find that this behavior is the same
> > without ISA.
> > RRAS and the TCP/IP stack, not ISA, handle the actual packet routing.
> >
> > --------------------------------------------
> > Jim Harrison
> > MCP(NT4, W2K), A+, Network+, PCG
> > http://isaserver.org/Jim_Harrison/
> > http://isatools.org
> > Read the help / books / articles!
> > --------------------------------------------
> > -----Original Message-----
> > From: Stefaan Pouseele [mailto:stefaan.pouseele@xxxxxxxxx]
> > Sent: Tuesday, December 27, 2005 4:58 AM
> > To: [ISAserver.org Discussion List]
> > Subject: [isalist] S2S VPN: why are static routes sometimes needed?
> >
> > http://www.ISAserver.org
> >
> > Hi,
> >
> > it seems that if a S2S VPN connection of type IPSec Tunnel is used and
> > if the remote tunnel endpoint can't be reached through the default
> > gateway, then you need to create extra static routes for the remote
> > network ID's reachable through that remote tunnel endpoint. I don't
> > understand why this is needed? Take note that there were no problems
> > in setting up the IPSec MM and QM SA's!
> >
> > To explain it better, here is a little diagram of the lab setup:
> >
> > 192.168.1.0/24
> > vvv
> > LAN-A -------- [ISA-A] ---+
> > 192.168.22.0/24 .10 !
> > +--- [RTR] --- Internet
> > ! .1
> > .30 !
> > [RTR-B]
> > ! .1
> > .10 !
> > LAN-B -------- [ISA-B] ---+
> > 192.168.44.0/24 ^^^
> > 192.168.11.0/24
> >
> >
> > On ISA-A:
> > ---------
> >
> > Remote Site Network contains:
> > - 192.168.11.10/32
> > - 192.168.44.0/24
> >
> > Default gateway: 192.168.1.1
> >
> > Static routes configured:
> > - 192.168.11.0/24 Gateway 192.168.1.30
> > - 192.168.44.0/24 Gateway 192.168.1.30 <<<< WHY is this one needed ???
> >
> >
> > On ISA-B:
> > ---------
> >
> > Remote Site Network contains:
> > - 192.168.1.10/32
> > - 192.168.22.0/24
> >
> > Default Gateway: 192.168.11.1
> >
> > No static routes configured.
> >
> >
> > Test:
> > -----
> >
> > From a host on LAN-B ping a host on LAN-A. Without the static route
> > '192.168.44.0/24 Gateway 192.168.1.30' on ISA-A, I can see the ping
> > request and reply on LAN-A but the reply never makes it back to LAN-B.
> > The ping reply just disappeared into thin air! Creating the static
> > route and bingo, it works. What's the logic behind this behavior?
> >
> >
> > Thanks,
> > Stefaan
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