871w am200 linksys modem config with global subnet of 16 ip addresses

By nickathan ·
Iwant to configure the 871w cisco router and am200 linksys modem to cooperate in a pppoatm connection from my isp.I use the modem in half bridge mode,so i receive the global static ip in the input of my 871w fa 4 far so good.
Using the default vlan 1 of my router i create the subnet of global ip given to me from my isp..
and define 1 ip from the working 14 to vlan 1 ,used as gateway from the rest of pc connected to the fa 0/1/2/3.I want to work without Nat,it is not necessary ,because the ips i have are routable and on the other hand i want to have full functionality with the ports.The problem is that the system works (my pc can access internet) only in Nat mode and in overload config ,,,If i disable this mode or i dont use nat overloadind none client pc can access the internet.

Any advice will be much appreciated...


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as long as your assigned the routable addresses

by CG IT In reply to 871w am200 linksys mode ...

by your internet provider, then sure, you don't need to use NAT. but if you don't have routable addresses assigned to you by your internet provider then you have to use NAT. you can not just decide to use routable addressing for hosts if they haven't been assigned to you. Those hosts will not be recognized on your internet providers network and the packets will simply be discarded. Only the host with the assigned address will be recognized and packets accepted.

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global ip conf for 871w and am200 linkjsysmodem

by nickathan In reply to as long as your assigned ...

Hi my friend....yes the subnet i use is given to me from my isp...what i afraid is that because i use the modem am200 linksys in halfbridge mode blocks the subnet ip and permits only the global static ip from my isp tp go through so the subnets ip are blocked,thatswhy the system works only in nat overload mode in my router...
as you know in overload mode any ip from subnet is replaced with the global static ip in the wan port (fa 4).

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don't think you understand Global local addressing.

by CG IT In reply to global ip conf for 871w ...

if your ISP assigns you a block of public addresses, you can then assign those public addresses to your hosts. Your router then does not need to use many to one NAT.

But if your ISP only assigns you 1 public address, then you must use NAT if you want the hosts behind the router to reach the internet.

you can not simply assign hosts addresses within the public subnet. the addresses will not be recognized by your ISPs network and quite possibly be dupicates of addresses assigned to other ISP customers.

So the bottom line is, if you have 10 hosts on your network, you would need a block of 10 Global public address assigned to you by your ISP. your would then assign your 10 hosts an address from that block. Your router would then not need to use NAT for those hosts. Your routers routing table will only need to know the destination network, mask and next hop router [and name servers]for those hosts to reach the internet. Depending upon what perimeter router you use, turning on a routing protocol such as RIP or OSPF would give the router the information it needs on destination networks, subnet masks and next hop router.

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What IP is assigned to fa4

by NetMan1958 In reply to 871w am200 linksys mode ...

Is it in the same subnet as the /28 you are using on Vlan 1?

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fa 4 ip

by nickathan In reply to What IP is assigned to fa ...

no...the ip assigned to fa 4 is the public static ip from my isp(it is coming from my am200 modem working in half bridge mode)and is connected to pstn line(adsl2 +) annex a..

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