WAN port and networking, lay-man question

There is a broadband modem (Aztech) with a network port (RJ45), and a port
of phone line. According to its manual, the modem is initialised with IP
192.168.1.1 as default.

There is an 5-port SMC router (one of them is a WAN port). The router is
initialised to 192.168.2.1 by default.

Since the modem and the router are at 2 different segments, I tried several
times to set the default IP of SMC router to 192.168.1.2 (I assume that they
cannot talk). However, the SMC router seemed to hang several times (the
modem was connected to the WAN port).

Later a guy came and reset the SMC router to its default (modem was
connected to the WAN port of router); it worked.

Is my assumption wrong, ie the segments 192.168.1.1 and 192.168.2.1 cannot
communicate ? Thanks.

Hello,

sl@exabyte a écrit :
> There is a broadband modem (Aztech) with a network port (RJ45), and a port
> of phone line. According to its manual, the modem is initialised with IP
> 192.168.1.1 as default.
>
> There is an 5-port SMC router (one of them is a WAN port). The router is
> initialised to 192.168.2.1 by default.

On what side ? LAN or WAN ?

> Since the modem and the router are at 2 different segments, I tried several
> times to set the default IP of SMC router to 192.168.1.2 (I assume that they
> cannot talk). However, the SMC router seemed to hang several times (the
> modem was connected to the WAN port).
>
> Later a guy came and reset the SMC router to its default (modem was
> connected to the WAN port of router); it worked.

What worked ?

> Is my assumption wrong, ie the segments 192.168.1.1 and 192.168.2.1 cannot
> communicate ? Thanks.

Yes, your assumption is wrong : it is the purpose of routers to allow
communication between different subnets. Think that one can communicate
with any public subnet on the internet thanks to all the routers out there.

On 08/07/10 15:18, sl@exabyte wrote:

> There is a broadband modem (Aztech) with a network port (RJ45), and a port
> of phone line. According to its manual, the modem is initialised with IP
> 192.168.1.1 as default.
>
> There is an 5-port SMC router (one of them is a WAN port). The router is
> initialised to 192.168.2.1 by default.
>
> Since the modem and the router are at 2 different segments, I tried several
> times to set the default IP of SMC router to 192.168.1.2 (I assume that they
> cannot talk). However, the SMC router seemed to hang several times (the
> modem was connected to the WAN port).
>
> Later a guy came and reset the SMC router to its default (modem was
> connected to the WAN port of router); it worked.
>
> Is my assumption wrong, ie the segments 192.168.1.1 and 192.168.2.1 cannot
> communicate ? Thanks.

The modem may get an address on its adsl facing port in the IPSs
network, it offers a lan address on it's rj45 of 192.168.1.1

The router gets an address on its wan port from the modem, and offers a
lan address on it's 4 lan ports of 192.168.2.1

The router has two addresses, the Wan side address that it probably gets
automatically from the modem, and the lan side address that's part of
its configuration:

The 4 lan ports on the router are probably connected to a switch

isp wan ~~~(a) modem (b)==(c) router (d)--- switch -[ ports ]

At a, the modem may have an ip address allocated by the isp
At b, the modem presents 192.168.1.1
At c, the router probably picks up a wan side address and netmask from
the modem using dhcp, this address is probably 192.168.1.x and the
netmask is probably 255.255.255.0
At d, the router presents to the internal lan network switch the address
192.168.2.1
Computers that plug into the ports probably get allocated an ip address
of 192.168.2.x and a netmask of 255.255.255.0 by the dhcp server in the
router.

Rgds

Denis McMahon

>
>> There is a broadband modem (Aztech) with a network port (RJ45), and a
>> port
>> of phone line. According to its manual, the modem is initialised with IP
>> 192.168.1.1 as default.
>>
>> There is an 5-port SMC router (one of them is a WAN port). The router is
>> initialised to 192.168.2.1 by default.
>>
>> Since the modem and the router are at 2 different segments, I tried
>> several
>> times to set the default IP of SMC router to 192.168.1.2 (I assume that
>> they
>> cannot talk). However, the SMC router seemed to hang several times (the
>> modem was connected to the WAN port).
>>
>> Later a guy came and reset the SMC router to its default (modem was
>> connected to the WAN port of router); it worked.
>>
>> Is my assumption wrong, ie the segments 192.168.1.1 and 192.168.2.1
>> cannot
>> communicate ? Thanks.
>
> The modem may get an address on its adsl facing port in the IPSs
> network, it offers a lan address on it's rj45 of 192.168.1.1
>
> The router gets an address on its wan port from the modem, and offers a
> lan address on it's 4 lan ports of 192.168.2.1
>
> The router has two addresses, the Wan side address that it probably gets
> automatically from the modem, and the lan side address that's part of
> its configuration:
>
> The 4 lan ports on the router are probably connected to a switch
>
> isp wan ~~~(a) modem (b)==(c) router (d)--- switch -[ ports ]
>
> At a, the modem may have an ip address allocated by the isp
> At b, the modem presents 192.168.1.1
> At c, the router probably picks up a wan side address and netmask from
> the modem using dhcp, this address is probably 192.168.1.x and the
> netmask is probably 255.255.255.0

This is the part that I did not get, ie the router gets an IP from the
modem.

Of course my wrong assumption too. But you see when I browse the network,
I think I cannot see computers in a different segment, eg Windows Explorer
does not show different segment.

> At d, the router presents to the internal lan network switch the address
> 192.168.2.1
> Computers that plug into the ports probably get allocated an ip address
> of 192.168.2.x and a netmask of 255.255.255.0 by the dhcp server in the
> router.

Thanks Denis and Pascal.