topic Re: Two network addresses on same network in Operating System - HP-UX

Two network addresses on same network

John Downs_1 — Fri, 12 Jul 2002 11:50:05 GMT

Greetings, we have a single network(no router) made up of HUBs and switchs, that serves both MS2000 PC's and HPUX workstations. The IS administrator is running out of addresses so they want to subnet the current address(using some of the bits of the third position). Something like this:
190.9.200.host and 190.9.201.host. They want to use these addresses on the same network. I always thought this was a big no no. Is this still true? What problems can occur when you do this?

-john

Re: Two network addresses on same network

harry d brown jr — Fri, 12 Jul 2002 11:53:49 GMT

190.9.200.host and 190.9.201.host are TWO Different IP's, as in:

192.9.200.1 and 192.9.201.1

What are you using for a subnet mask? gateway?

live free or die
harry

Re: Two network addresses on same network

V. V. Ravi Kumar_1 — Fri, 12 Jul 2002 12:20:27 GMT

hi,

190.9.200.* is a class C address 190.9.200.host and 190.9.201.host both are two different networks. since it is a single n/w with hubs and switches, u can use it.

regds

Re: Two network addresses on same network

John Downs_1 — Fri, 12 Jul 2002 12:35:10 GMT

Hi I don't know what the subnet mask will
be, I assume they will have the correct one. In the past I have worked on larger networks and all subnets where separated with a router.

For example would there be any problems with have two machines, each machine with a different network address, connected to the same hub or switch? Assume that the subnet masks are correct.

-john

Re: Two network addresses on same network

PIYUSH D. PATEL — Fri, 12 Jul 2002 12:41:30 GMT

Hi,

Ravi : This address is a class B address and not class C address.

You can do a subnetting but then the subnet mask also changes and hence you will need to change the subnet mask also at all the places and change lot of configurations.

After subnetting you will have to use routers in between the subnets.

Piyush

Re: Two network addresses on same network

Steven Sim Kok Leong — Fri, 12 Jul 2002 12:56:50 GMT

Hi,

If you are running out of IP addresses, subnetting actually reduces the number of IP addresses you can use because for every subnet you create, you need to allocate one IP for the network address and one IP for the broadcast address.

Theoretically, if you have 190.0.200.0/24 and a 190.9.201.0/24 subnets within a single 190.9.0.0/16 subnet, inbound traffic can still be routed properly if your interface uses an IP in the 190.9.0.0/16 network i.e. 255.255.0.0 netmask. Theoretically, outbound traffic should still work as long as the router interface receives the packet because the IP address still belongs to its 190.9.0.0/16 network.

Even then, both 190.9.200.0/24 and 190.9.201.0/24 subnetworks will not be able to communicate with each other though traffic can be routed to networks outside 190.9.0.0/16.

To allow them to communicate with each other, your router interface must support IEEE 802.1q vlan tagging so that your router interface has two IP addresses, one residing within 190.9.200.0/24 and one residing within 190.9.201.0/24.

In practice, I have only used a single hub to house two different subnets (one routable public network and one private non-routable network). That works for me.

Hope this helps. Regards.

Steven Sim Kok Leong

Re: Two network addresses on same network

Steven Sim Kok Leong — Fri, 12 Jul 2002 13:04:48 GMT

Hi,

Oh, I noticed from your query that you are using no routers. In that case, 190.9.200.0/24 subnet and 190.9.201.0/24 subnet will not be able to communicate with one another on the same hub or switch. But, within each subnet, they can still communicate with one another for i.e. intra-subnet communication works but not inter-subnet communication does not work for:
- hub
- switch with/without use of vlans

When machine A in 190.9.200.0/24 tries to communicate with machine B in 190.9.201.0/24, it checks its routing table. Because the entry does not match its subnet 190.9.200.0/24, it will use the default gateway/route to send the packet. However, because there is no default gateway/route, the packet cannot be routed. You will receive error messages alike "No route to destination".

Hope this helps. Regards.

Steven Sim Kok Leong

Re: Two network addresses on same network

V. V. Ravi Kumar_1 — Fri, 12 Jul 2002 13:19:28 GMT

Thanks Piyush!
hi john,

very sorry! its a class B address only, i confused on 190 and 196, very sorry again.

but still u can connect to the same hub, with the different addresses.

regds

Re: Two network addresses on same network

John Waller — Fri, 12 Jul 2002 13:29:01 GMT

John,

Asuming a correct subnet mask setting, e.g. 255.255.0.0 as a standard class B subnet mask, you will not have any problems mixing 190.9.200.xxx with 190.9.201.xxx or even 190.9.230.xxx on the same switches or hubs.

Working with the 7 layer OSI model, hubs work at level 1(physical) and switches at level 2 (data link) both these are below level 3 (network) where the physical IP addressing comes into play.

Re: Two network addresses on same network

KapilRaj — Sat, 13 Jul 2002 04:10:25 GMT

Hi,

You can hv two TCP/IP Networks in a single Physical Network. There is no problem. But there are some, here it goes.....

Let's take an example

Machine A : -

IP Add: 190.201.201.1
SUBNET: 255.255.255.0

Machine B :-

IP Add: 190.201.200.1
SUBNET: 255.255.255.0

01. Do not expect Machine A & B to communicate together using TCP/IP. Though they are connected Physicaly, they won't communicate without a router.

02. As you hv. Windows 2000 PC/s . One of them can be configured as a router for your network. Install two ethernet cards in the machine, enable IP routing.Let both the Ethernet interfaces goto the same switch/ hub.

A solution for you,

I just can't digust with a class-B network you are running out of IP Addresses.... If you use

IP Add: 190.201.XX.XX
SUBNET: 255.255.0.0

you get 65536 IP adds.

Hope it helps you

Hv a nice time

kaps