IP Addressing in PPP

[Meenakshi]

I would like to know about the IP address management in PPP connection.
I use a DSL modem to connect to my ISP.
I am provided with a dynamic IP 122.164.40.82. This is the client IP address. (In properties Obtain IP address automatically option is enabled)
Subnet mask is 255.255.255.255
My server IP address is 203.145.161.1.
The default gateway is also 122.164.40.82.
I understand that because of the subnet mask, my computer is in a single host network.
When I trace route (tracert google.com) to any site my first hop is to the server IP followed by several entries.
How can my computer(which is provided with a Class A address) connect to the server(which is provided with a Class C address) without a gateway or a router in the intermediary?

Regards
Meena

[pushkin_singh]

Hi Meena

First of all when you say your Server Ip address (203.145.161.1) what server is this DNS or something else

I am guessing this is your DNS server, which might be why this is your first hop when you do a traceroute which in turn queries your DNS to resolve this DNS to IP & forward it to relevent device.

The reason you are unable to see intermediate routers, etc at ISP end because they are Layer 2 ATM or F.R switches and traceroute is used to determine Layer 3 connectivity. You can connect any system to other irrespective of fact what class (A,B or C) of address its has got by routing it correctly....That's the wonder of Networking

I hope this clear things up for you.

Pushkin

[RFmax]

Are you sure about that subnet mask? The /32 typically designates the broadcast addr for that particular subnet. The smallest subnet is usually defined by /30.

A subnet mask of 255.255.255.254 breaks a Class C network into subnets that have only two addresses each. These addresses would be the network address and announce address, which would be unusable as host addresses. The netmask 255.255.255.255 would define a network of only one device. About the only time this mask could be useful is defining a loopback, an IP device that can only talk to itself.
_________________
CWNA, CWSP, K0PBX

[Meenakshi]

Do you mean to say that a system with an IP 44.168.100.2 can connect to an IP 192.168.100.2 without any router or gateway??
If so how do you specify the routing entry in the above case??

My office has a network 192.168.100.0
I tried to change the IP of one of my machine to 44.168.100.2 but the machine became isolated and it was not possible to send or receive any packets.
My subnet mask is 255.255.255.0
Default gateway: 192.168.100.1
When I did the above IP change, my default gateway became 0.0.0.0
When I tried to ping 192.168.100.5, I couldn't establish the connection.
How do I perform routing in this case??

Regards
Meena

[pushkin_singh]

Hi Meena

First of all you got to be clear about how you network is been set-up and what are you trying to establish here

Anwyay as per given info the address 44.168.100.2 is a public IP address given by your ISP which is routable & will be assigned to your Router or Gateway PC (External or WAN interface). The IP 192.168.100.2 is your private LAN Non-routable address which is assigned by your router/gateway to your internal network so there will be a Default route statement (IP route 0.0.0.0 0.0.0.0 44.168.100.2) on your router pointing to your Public IP (44.168.100.2) which means any address request which your internal network is unaware of will be fwd to Public IP.

You don't need to perform any manual routing statements on your router in your case until & unless you want to route any other networks.

Hope this helps

Pushkin.

[Meenakshi]

How do I connect a class A IP address to class C IP address??
You had specified that machines can be connected irrespective of their classes by routing them correctly??
How is it possible??

I use a PPP connection (to ISP) for internet.
My ISP server is 203.145.161.1
The connection uses dynamic IP addressing.
I am specified with a client IP of 122.164.40.82
When I trace route my first hop is to 203.145.161.1
But that is not my DNS Server.

How does PPP work?
How is the IP address specified and how is the connection established?
How does the client and server communicate in the above case?

It would be great help if someone can help out in this regard or suggest a good material on the above topic?
I tried to search but I am not able to get the exact details.

Regards
Meena

[RFmax]

Just to let us understand your network it might be the best to run the command ipconfig /all and publish it here. I think you maybe using the wrong terminology and it is slightly confusing.

As for communicating between different networks, that is exactly what routing is.

http://en.wikipedia.org/wiki/Routing
_________________
CWNA, CWSP, K0PBX

[pushkin_singh]

Hi Meena

Wait & think for a minute, you answer is in your question itself

[darkt3ch]

Yea abit confusing but Ill have a stab and try explain.

My IPconfig results:

Ethernet adapter Wireless Network Connection:

Connection-specific DNS Suffix . :
IP Address. . . . . . . . . . . . : 10.1.1.3
Subnet Mask . . . . . . . . . . . : 255.0.0.0
Default Gateway . . . . . . . . . : 10.1.1.1

***
IP Address - This is my PRIVATE IP for my PRIVATE network. This IP address means nothing on the internet

Subnet Mask - You can only talk to hosts on the same subnet. This is used by routers to "read" IP addresses.

Default Gateway - This is my router/modem's IP address. So when my machine wants to access anything this is where it will send the data packets (more on this in a sec).

My ISP asigned IP:

60.240.85.166

This is my PUBLIC IP which is obviously used over the internet.

Googles IP:

72.14.207.99

This is our destination IP. So it is where we want to eventually connect to and establish a "session".

Ok so a little more on the default gateway. this is your modem/router it has 2 (or more IP Addresses):

My ISP Assigned IP Address (60.240.85.166)
My Private network address (10.1.1.3)

So if I am connecting to google.com, my computer (10.1.1.3) will talk to the default gateway (10.1.1.1).

My Computer -----sends packet to --->>>> Router (Default gateway)

This packet is a set of instructions for the router which says "I want to talk to google.com". So your router will then your router will send the packet to the ISP's routers which recieve the instructions and then pass it on to more routers (Do a "tracert google.com") The packet gets passed along a path with many routers along the way until it finally reaches 72.14.207.99 (google.com). Now that it has reached its destination (72.14.207.99) google's routers will then pass it into their private networks to find a server that can carry out the instructions for the packet.

OK so the google.com webservers have the packet. Now they Will send a packet back to you, which will travel through the many routers etc. until it reaches your computer. And this has now created the session between my computer and google.com so we can talk freely and each packet sent contains a new set of instructions.

So there we have it... The life of a packet. kinda longer than I planned so I hope it helped.

Cheers!!
_________________
Your only as strong as the drinks you mix, the pills you dance on and the friends you roll with!!!

[Meenakshi]

My network is also quite similar to yours.
We have a LAN and a diap up connection.
The dial up connection is configured in 192.168.100.1
We use ICS (Internet connection sharing)
So, any communication to Internet is sent to the default gateway machine 192.168.100.1 which is in turn connected to Internet.

The 192.168.100.1 machine has another public IP Address dynamically assigned by ISP which is 122.164.40.82
192.168.100.2 machine's default gateway is also 122.164.40.82
I have got a beetel PPP internet connection.
In its connection status I was able to find 2 entries

Client IP Address : 122.164.40.82
Server IP Address : 203.145.161.1

In TCP/IP properties I found the 'Use default gateway on remote network' option checked.

A few entries from routing table (route print) of the machine 192.168.100.1 include

N/W Dest Netmask Gateway
0.0.0.0 0.0.0.0 122.164.40.84
203.145.161.1 255.255.255.255 122.164.40.84

When I want to talk to google my destination IP would be say 73.23.90.4
When I tracert route (tracert google.com) I find the first hop to be 192.168.100.1 (my defaulf gateway) and then the next hop is to 203.145.161.1 and not 122.164.40.84
I think that in above case the routing entry that matches is the default route in which case the next hop should be to the default gateway.
But at no point of time it hops to 122.164.40.84

But why is 122.164.40.84 hop missing??
Why is the packets directly being sent to 203.145.161.1??
Any help in this regards would be greatly appreciated.

Regards
Meena

[RFmax]

If I understand your topology correctly, those addrs are bound to different interfaces on the same device, therefore it is not considered a hop.
_________________
CWNA, CWSP, K0PBX

[Meenakshi]

That makes one point clear.
Thanks for that.

The other question I have is how do my machine (192.168.100.1) with a dynamic client IP 122.164.22.85 connect to my ISP server IP 203.145.161.1 directly without any intermediary because they both belong to different classes.

As far as I know in order for 2 machines from different classes to connect there must be a gateway.
If that is true then I should get those intermediate IP's when I trace route to google.com

When I trace the hop to 122.164.22.85 is left. BUt that is justified from the previous reply. How does the communication between 122.164.22.85 and 203.145.161.1 take place directly?
Is it because of PPP connection that the client IP directly communicates to Server Ip without any intermediaries??

Regards
Meena

[RFmax]

What happens when you ping 122.164.40.84?

Also the reason that you are going directly to 203.145.161.1 is the second entry in the routing table below. The .84 router is forwarding directly to it.

N/W Dest Netmask Gateway
0.0.0.0 0.0.0.0 122.164.40.84
203.145.161.1 255.255.255.255 122.164.40.84

I am not positive as to how a router responds to trace route if it has ICMP setup to not respond, that is why I asked what happens when you ping .84.
_________________
CWNA, CWSP, K0PBX

[Meenakshi]

There is an entry for 203.145.161.1
But when I connect to google my packet transmitted will have its destination IP as (say) 74.34.90.3, right?
Then how do the entry for destination network 203.145.161.1 match in the routing table?
When I ping .84 connection is established.
No problems in that.

Regards
Meena