VOIP with a linksys PAP2

[Kevin J. Cummings]

THUFIR HAWAT wrote:
> On 6/12/05, Kevin J. Cummings <cummings at kjchome.homeip.net> wrote:
> ...
> 
>>Your internet connection is WI-FI????  Is this a Linksys router with
>>WI-FI?  Is it configured to route multiple network traffic or just your
>>linux machine?  Does it know about the "network" on your Linux machine's
>>eth1?
> 
> 
> the internet connection is from
> <http://usa.asus.com/products/communication/wireless/wl-330g/overview.htm>
> into eth0 and a hub is plugged into eth1, then a linksys PAP2
> <http://www.linksys.com/products/product.asp?prid=651&scid=38> into the
> hub. 

OK, I assume that the WL330g is a wireless access point that connects to 
a local wireless router through which your Linux box can connect to the 
internet.  I'll also assume that it connectes to an ethernet card in 
your computer which is eth0.  Further, I'll assume that this connection 
is working fine.

You probably have a routing table (ip route or route) which looks 
something like:

192.168.1.0/24 dev eth0  proto kernel  scope link  src 192.168.1.1
default via 192.168.1.2 dev eth0

(the actual number might be different for you depending on your network)

> I think all I need is the masquerading..?  but, I'd first like to test
> the hardware with pings, or something.

In order to ping the PAP2 from Linux, both need to have their network 
interfaces properly configured.  They need to be on the same "subnet", 
and your routing table needs to be able to send the packets over the 
correct ethernet device (eth1).  Once you know what the IP addresses 
are, you can use them to "ping" the devices.  If you don;t have the 
properly configured, you can't ping.

>>If PAP2 is plugged into a HUB, then you don't need a crossover cable,
>>you want a straight through.  Is your HUB a router, a switch, or a
>>bridge?  A switch doesn't need configuring, a router may.
> 
> 
> according to the box:
> 
> wisecom 8 port 10 base-T hub
> 
> compliant with 10base-t, 10BASE2 and 10BASE5 specifications of the
> IEEE 802.3 standard.

This is a standard 10base-t 8 port hub with 3 different upload ports, 
which you probably don't need to use.  It cares not about the network it 
is plugged into.  Any packets which arrive through 1 of the 8 ports will 
be re-transmitted out the other 7 (and the active upload port if its in 
use).  If you only have your computer and the PAP2 plugged into it, then 
the 2 should be able to talk to each other through the port.

> and, it's an ethernet HUB for WorkGroup
> 
> I think it's a switch, definitely not a router.

No, a switch can handle multiple speeds and "remembers" which ports 
certain devices are attached to (via their MAC addresses) and only 
transmits the incoming packets out to the one destination port.
Switches cost more than plain hubs.

>>How is the telephone plugged into a hub?   Ethernet hubs don't (usually)
>>have POTS (analog telephone) jacks.  I would think that your telephone
>>should be plugged into something which is not a network or ethernet
>>router, but some kind of telephony equipment.  (Isn't that what your
>>PAP2 is?)

According to the PAP2 documentation I looked at, it has 2 telephone 
ports.  You should plug your telephones into the PAP2.

> the PAP2 is plugged into the hub. the hub is plugged into eth1.

OK, that's good.

>>>on boot I got a message about lost packets, but it went by too fast.
>>>I've installed firestarter.  I need to set up dhcp, perhaps.  how do I
>>>ping, or ipconfig the hub?
>>
>>Have you checked your log files (/var/log/messages)?  used the "dmesg"
>>command to see your boot-up messages?  Just because you didn't read them
>>on the screen doesn't necessarily mean they are gone forever!
> 
> 
> I'll check /var/log/messages, thanks.

I saw your boot messages, it looks like eth1 is being configured via 
DHCP as 198.162.2.1  and your eth0 configuration is failing to start?
Are you sure you have them correctly identified?  What does "route" give 
you for output?  One of your interfaces is acting like there is no cable 
plugged into it....  What does "route" tell you?  Where does your 
"default" route go?

> 
>>Does your Linux box have IP forwarding configured?  Is the eth1 metwork
>>publicly routable?  If not, have you configured Linux to do NATing?
> 
> 
> this I haven't yet done.

Then your PAP2 won't be able to find its VOIP service until you do this.
Using NAT will allow your Linux computer to masquarade the TCP/IP 
packets out to the internet and back to the PAP2 for you.  You'll also 
need to make sure that IP forwarding is turned on.  Without it, Linux 
won't even try to route the packets from eth1 to eth0 and vice versa.

>>How does your PAP2 get its IP address?  If you don't know, you probably
>>need to configure a DHCP server on Linux as well!  Is there anything
>>else on the eth1 network (ie, is anything else plugged into your hub)?
>>If so, how are they allocated IP addresses?
> 
> 
> the hub just has two connections.  one to the computer, one to the
> PAP2.  I need to find out how the allocate IP addresses.
> 
>>This is all *basic* network configuration....
>>
> 
> 
> I know it's basic, but it's not something I know about yet.

Its pretty simple once you understand it.  B^)

INET (via WIFI) <-> wl-330g <-> eth0 [linux] eth1 <-> hub <-> PAP2

eth0 needs an IP ADDRESS, NETMASK, and BROADCAST address in order to 
talk with the wl-330g which must somehow must communicate with your 
wireless INET connection.  It would not surprise me to find out the the 
wl-330g provides a DHCP/NATed subnet to eth0.  eth1 will require the 
same, though its possible they are being handled via DHCP from the PAP2. 
  You will probably need to make saure that the 2 ethernet networks are 
on different subnets for ease in routing (and NATing) and so that the 
wl-330g doesn't have to know anything about the network connection of 
eth1.  You can use "unroutable" IP address ranges locally for your 
internal private networks and handle the allocation of those addresses 
by yourself.

Looks like you're going to be having a lot of fun getting this to work!
Enjoy!

-- 
Kevin J. Cummings
kjchome at rcn.com
cummings at kjchome.homeip.net
cummings at kjc386.framingham.ma.us