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Thread: Is it possible to use Cisco 877 behind DSL-modem

  1. #1
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    Dec 2011
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    Is it possible to use Cisco 877 behind DSL-modem

    I have been using a business DSL-connection and it cannot be used with some other router so I have to use the one that has been provided to me from the provider, In my case I just wanted to know that is it possible to use the Cisco 877W-G-E-K9 behind the modem and also set it up as VPN-server?? Is there anyone who has an idea about it and can help me out as well??

  2. #2
    Join Date
    May 2011
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    460

    Re: Is it possible to use Cisco 877 behind DSL-modem

    I have been using a business DSL-connection and it cannot be used with some other router so I have to use the one that has been provided to me from the provider, In my case I just wanted to know that is it possible to use the Cisco 877W-G-E-K9 behind the modem and also set it up as VPN-server?? Is there anyone who has an idea about it and can help me out as well??
    Before I suggest you something about this I just want you to make sure that you are having the Cisco 887 or Cisco 877, I am asking so because the Cisco 877 supports IPSec VPN when used with a K9 IOS,so just check it out and then let me know what you have for further help.

  3. #3
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    Dec 2011
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    Re: Is it possible to use Cisco 877 behind DSL-modem

    I have crossed check it and I am having the Cisco 877W-G-E-K9 and here is some more information about it:
    • It is having a POTS RJ11-connection behind it
    • ISP-modem forwards all the ports to 122.182.10.142

    So I just wanted to know that is there a way to configure the cisco and make it work as a router behind the modem that I am having??

  4. #4
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    Re: Is it possible to use Cisco 877 behind DSL-modem

    I will suggest you to use any of the FE port in order to connect to the ISP modem's RJ45 and then configure it as per the following:
    877(config)#int f0
    877(config-if)#no switchport
    877(config-if)#ip address (your ip address) 255.255.255.252
    877(config)#int vlan 1
    877(config-if)#ip address (your internal address)
    877(config)#ip route 0.0.0.0 0.0.0.0 ISP_MODEM_IP
    Just try it out and then let me know what you get.

  5. #5
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    Re: Is it possible to use Cisco 877 behind DSL-modem

    I have tried it out but then it is not working in my case, I have found that the ISP-modem is having the 122.182.10.142 as ip but then I did not found DHCP configured and all ports are simply forwarded to 122.182.10.143 which I think is cisco router but then I am not very sure about it. Below is the default configuration of the cisco877 that I am using:
    Internal network of cisco = 10.10.10.1 with DHCP.
    The dialer and the NAT is not configured by now, are you having some template that I can use to configure the cisco without any problem??

  6. #6
    Join Date
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    Re: Is it possible to use Cisco 877 behind DSL-modem

    I will suggest you to use the "no switchport access vlan" command, just for e.g.
    877(config-if)#no switchport access vlan
    877(config-if)#(your ip address) ?
    A.B.C.D (your ip address)
    dhcp IP Address negotiated via DHCP
    pool IP Address autoconfigured from a local DHCP pool
    Just try it out and then let me know if it is making any difference.

  7. #7
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    Re: Is it possible to use Cisco 877 behind DSL-modem

    I will suggest you to change the ip route 0.0.0.0 0.0.0.0 to ip route 0.0.0.0 0.0.0.0 122.182.10.142 and after that use the above command and then give it an ip address with the same range as that of the router, in your case which is Belgacom BBox which has been configured on the router which is on the dhcp pool, just try ot make the above changes and then see if it is helping you.

  8. #8
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    Re: Is it possible to use Cisco 877 behind DSL-modem

    I have found that the 877 FE ports have been set to Layer 2 by default so I don’t think that the above will work, rather try this out:
    877(config)#vlan 10
    877(config)#int vlan 10
    877(config-if)#ip add 122.182.10.142.2 255.255.254.0
    877(config-if)#int f0
    877(config-if)#switchport access vlan 10
    Check it out and then let me know what you get, best of luck.

  9. #9
    Join Date
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    Re: Is it possible to use Cisco 877 behind DSL-modem

    877(config)#vlan 10
    877(config)#int vlan 10
    877(config-if)#ip add 122.182.10.142.2 255.255.254.0
    877(config-if)#int f0
    877(config-if)#switchport access vlan 10

    I have tried out the above solution as well but then they are not helping me out, is there any other thing that I can try out??

  10. #10
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    May 2011
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    Re: Is it possible to use Cisco 877 behind DSL-modem

    I think that your modem might be DHCP and NAT, if possible then just configure your 877 as following:
    int vl1
    no ip nat in
    int vl10
    no ip nat out
    ip add dhcp
    no ip nat inside source list 101 interface vlan 10 overload
    no ip route 0.0.0.0 0.0.0.0 122.182.10.142
    ip route 0.0.0.0 0.0.0.0 dhcp

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