Example config for 831 behind ISP router

Discussion in 'Cisco' started by Erwin Drager, Apr 15, 2005.

  1. Erwin Drager

    Erwin Drager Guest


    I need to install a Cisco 831 ethernet router behind an Alcatel VOIP
    router. Because of ISP restrictions on the VOIP part, I have to use
    the Alcatel box, and need to place the Cisco behind that to enable use
    of VPN connections. (currently we use a Cisco 836 with built in ADSL

    We have been trying to get this to work in a test environment, but
    until now to no avail.

    A short layout of what we need:

    Public interface with public IP
    Alcatel VOIP Router
    LAN interface (
    E1 interface (
    Cisco 831
    E0 interface (

    Using this setup, without having set any restrictions on traffic, we
    are unable to ping beyond the LAN interface of the Alcatel coming from
    the Internet side (using a lab so not actual internet), and not beyond
    the E1 interface coming from the LAN.

    Does anyone have a sample config of a setup like this i could take a
    look at?

    Thanks in advance,

    Erwin Drager
    Erwin Drager, Apr 15, 2005
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  2. Erwin Drager

    sam Guest

    You can take a look at a cisco 2611 router configuration that i use
    (see my different last posts). The situation where i use it is
    similary as yours.
    Good luck
    sam, Apr 15, 2005
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  3. Erwin Drager

    Chris Guest

    So does the Alcatel have a route to the 10.x.x.x network?

    Chris, Apr 15, 2005
  4. Erwin Drager

    Erwin Drager Guest

    Thanks Sam, will take a look at your config.
    Erwin Drager, Apr 18, 2005
  5. Erwin Drager

    sam Guest

    Notice that i have a problem with that config : when the isp change
    the Internet IP (by dhcp) , the c2611 does'nt see the changement (and
    the connectivity to internet is lost). And i don't know how to solve
    the problem ... (see my post IP address by dhcp on a cisco2611... I
    hope you don't have this pb)
    sam, Apr 18, 2005
  6. Erwin Drager

    Erwin Drager Guest

    It didnt, and that was part of the solution!

    I was finally able to solve everything but one issue today (more about
    that in a new post ;-)

    Erwin Drager, Apr 21, 2005
  7. Erwin Drager

    Erwin Drager Guest

    We dont have that problem since our ISP assigns fixed IP adresses :)

    Erwin Drager, Apr 21, 2005
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