Site to Site VPN works. How does traffic been routed?

Discussion in 'Windows Networking' started by eric, Feb 24, 2004.

  1. eric

    eric Guest

    I have setup a site to site VPN for our remote branch using pptp. The
    following is the setting:

    head quarter branch
    T1 (192.168.1.x) 756K DSL(192.168.2.x)
    through (DHCP)
    permanent VPN

    I have branch DHCP server pointed its DNS to DC's integrated DNS. If
    the name can not be resolved, it will go to forwarder.

    Everything works fine. My question is how does branch clients access
    internet? Does all the internet traffic route through HQ's T1?
    Whenever the branch VPN server connected to HQ vpn server, HQ's T1
    traffic increase about 50%. Is it normal? Is there anyway to tune
    eric, Feb 24, 2004
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  2. eric

    Tom Thompson Guest

    I think it depends on how you have your branch clients default gateway

    Please correct me if I'm wrong, but I think if the branch clients have a
    default gateway of the branch site router, the branch site clients will use
    the DSL link. If the DG is set as the headquarters router then the branch
    site clients use the T1

    Tom Thompson, Feb 24, 2004
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  3. eric

    Bill Grant Guest

    It depends on how the link is set up. Normally these are set up so
    that local machines access the Internet through the local router, and only
    inter-office traffic is sent through the VPN link. The only way to know for
    sure is to look at the routing table of the routers involved.
    Bill Grant, Feb 25, 2004
  4. It isn't very complex Eric.

    If the LAN is a single subnet (looks like yours is) then the clients simply
    use the VPN Device as the Default Gateway. The VPN Device itself is smart
    enough to know the difference between Internet traffic and your "intranet"
    traffic and handle it properly. Routing inside the VPN Device is pretty much
    automatic because the VPN link is considered a "Directly Connected Network"
    and due to that alone will already have a routing table entry.

    Yes, the traffic usage will jump up because you are running both Internet
    traffic and "intranet" traffic on the same T1. Also VPN just on its own has
    much more overhead in the Protocols than just straight TCP/IP traffic.

    VPN is not a very big "performer". It is not as efficient as a private
    leased line, but it is cheaper, which is probably the biggest legitiment
    attraction to it. But due to all the marketing "hype" everyone is in a mad
    scramble to setup VPNs, just like they were all in a mad scramble to get on
    the Internet back in the mid 1990's. Then they become confused and
    disappointed that is doesn't perform as smoothly and quickly as the older
    leased lines.

    We have over 20 sites connected by VPN from all across the US and Puerto
    Rico. It used to be all done with lease lines, now it is VPN. The change
    came due to cost savings, not because VPN is better (because it is not

    I guess I have to get on my VPN Soap Box and "spew" once in a while. :)
    Phillip Windell, Feb 25, 2004
  5. eric

    Bill Grant Guest

    Another thing which can make VPN seem slow is using ADSL. ADSL routers
    are designed to give you faster download speeds, usually by a factor of 4
    (like 64k/256k). If you use these for a VPN link, the VPN traffic runs at
    the lower speed, because all traffic is is an upload as far as one of the
    routers is concerned. Add the inevitable Internet holdups and
    encryption/encapsulation overheads and it is not speedy!

    Bill Grant, Feb 26, 2004
  6. eric

    Tom Thompson Guest

    True, our offices used this configuration for over a year. I was extremely
    slow , so we had to upgrad to a T

    Tom Thompson, Feb 26, 2004
  7. That makes me want to check on mine at home. It is supposed to be 256 both
    ways, but what they tell me and what really happens could be two different
    things. I use only a DSL modem (no router) if that makes any difference,
    but I know my VPN performance is miserable.


    Phillip Windell [MCP, MVP, CCNA]

    Phillip Windell, Feb 26, 2004
  8. eric

    Bill Grant Guest

    If it's genuine DSL, it should be symmetric (same both ways). The A in
    ADSL stands for Asymmetric, indicating not balanced.

    Bill Grant, Feb 27, 2004
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