purpose of network id and broadcast id ?

jeret

i have some questions which is a bit confusing to me. hope someone here can help me.

for example if i had given an IP address of 192.168.1.200 and subnet mask of 255.255.255.192, and i have to find how many networks, how many hosts for each network and the network ID and broadcast ID. I will get something like this :

---

192.168.1.0 *** NETID
192.168.1.1 FFF
192.168.1.62 LLL 1
192.168.1.63 *** BRODCAST

---

192.168.1.64 *** NETID
192.168.1.65 FFF
192.168.1.126 LLL 2
192.168.1.127 *** BRODCAST

---

192.168.1.128 *** NETID
192.168.1.129 FFF
192.168.1.190 LLL 3
192.168.1.191 *** BRODCAST

---

192.168.1.192 *** NETID
192.168.1.193 FFF
192.168.1.254 LLL 4
192.168.1.255 *** BRODCAST


Now, the FFF - LLL(ip range) i know are for the clients like computers, printers...etc. What about the network id and broadcast id for the each network, where and how do i use them? does the broadcast id and network id for routers? This is where i can't really understand.

What will be the subnets mask be for each of these four different networks?

Thanks and regards


jeret

Brinomite

Hi Jeret,

So I am still kind of new to the whole subnetting thing myself but here is kind of how I understand it. Anyone with more experience with subnetting or a better understanding please correct me if I'm wrong.

You can think of the subnet mask as the "neighborhood" and the network ID's divide up the neighborhood into "streets." Then think of the host IP addresses as the "house numbers" on the street. So using your example it looks like this:
Neighborhood (subnet mask): 255.255.255.192
Street Name (network ID): 192.168.1.192
House Address (host IP): 192.168.1.200

Subnetting gets this information by using binary ANDing. I worked out a few examples to hopefully help illustrate this.

Example 1
11000000.10101000.00000001.00011000 =192.168.1.24 (Host IP)
11111111.11111111.11111111.11000000 =255.255.255.192 (subnet mask)
11000000.10101000.00000001.00000000 =192.168.1.0 (Netowrk ID)

Example 2
11000000.10101000.00000001.01101110 =192.168.1.110 (Host IP)
11111111.11111111.11111111.11000000 =255.255.255.192
11000000.10101000.00000001.01000000 =192.168.1.64 (Network ID)

Example 3
11000000.10101000.00000001.10101111 =192.168.1.175 (Host IP)
11111111.11111111.11111111.11000000 =255.255.255.192 (subnet mask)
11000000.10101000.00000001.10000000 =192.168.1.128 (Network ID)

Example 4
11000000.10101000.00000001.11001000 = 192.168.1.200 (Host IP)
11111111.11111111.11111111.11000000 =255.255.255.192 (subnet mask)
11000000.10101000.00000001.11000000 =192.168.1.192 (Network ID)

If you take any arbitrary IP address that falls within one of your subnet ranges and "AND" it you should get a better feel for how this works out.

So to answer your questions:
What do you do with the network ID and broadcast addresses? Nothing, the router will sort this out through ANDing.
What is the subnet mask for the 4 different subnets? 255.255.255.192 for all of them because they are all in the same "neighborhood."

I also found Professor Messer's videos on IP Addressing help. Check out the videos in section 1.3 IP Addressing here: Professor Messer's CompTIA N10-005 Network+ Training | Professor Messer - CompTIA A+, Network+, Security+, Linux, Microsoft Technology Training

Samo3411

The network ID is used by routers so they have some thing like any address belong to 192.168.1.0/24 network send it over to this router. the Broadcast ID is used by nodes as the destination address when they want to send a broadcast like Arp requestes.

Darril

Brinomite wrote: »

You can think of the subnet mask as the "neighborhood" and the network ID's divide up the neighborhood into "streets." Then think of the host IP addresses as the "house numbers" on the street. So using your example it looks like this:
Neighborhood (subnet mask): 255.255.255.192
Street Name (network ID): 192.168.1.192
House Address (host IP): 192.168.1.200

This is a good analogy but you might like to fine tune it a little.

You can think of the *network ID* as the "neighborhood". Then think of the host IP addresses as the "house numbers".
The subnet mask helps define the network ID.

From a big picture perspective, consider this classful address:
Network ID: 192.168.0.0
Subnet mask: 255.255.255.0
(I realize that 192.168.0.0 isn't a common example, but it is valid and helps illustrate the point.)

Valid host IP addresses in the "neighborhood" for the "house numbers" are: 192.168.0.1 through 192.168.0.254
The network ID is 192.168.0.0
The broadcast address is 192.168.0.255

Here's what is looks like if this is not a classful address:
Network ID: 192.168.0.0
Subnet mask: 255.255.0.0

Valid host IP addresses in the "neighborhood" for the "house numbers" are: 192.168.0.1 through 192.168.255.254
The network ID is 192.168.0.0
The broadcast address is 192.168.0.255

Notice that in both of these examples, the network ID (without the subnet mask) looks the same. However, the subnet mask defines them with two completely different host IP address ranges.

Using your original analogy, you can divide the neighborhood into streets with subnetting. For example, starting with 192.168.0.0 and 255.255.255.0, you can divide it into two subnets:

Subnet 1
192.168.0.0
255.255.255.128
Host IP address range: 192.168.0.1 through 192.168.0.126
Broadcast IP: 192.168.0.127

Subnet 2
192.168.0.128
255.255.255.128
Host IP address range: 192.168.0.129 through 192.168.0.254
Broadcast IP: 192.168.0.255

Hope this helps.

Darril

@jeret, in response to your original questions, this might help.
purpose of network id


Consider this network:
Subnet1 -> Router1 -> Subnet2 -> Router2 -> Subnet3
SysA . . . . .. . . . . . . . . . . . . . . . . . . . . . . . SysW
SysB . . . . .. . . . . . . . . . . . . . . . . . . . . . . . SysZ


All of the IP addresses in Subnet1 must have the same network ID. Similarly, all the IP addresses in Subnet2 must have the same network ID, and all the IP addresses in Subnet3 must have the same network ID.


When SysA sends traffic to SysB, TCP/IP recognizes they both have the same network ID so they are both on the same subnet, Subnet1 in this case. TCP/IP sends the traffic directly to SysB.


When SysA sends traffic to SysZ, TCP/IP recognizes they both have different network IDs so they are on different subnets. TCP/IP sends the traffic to the default gateway, which is the near side of Router1. Router1 sends it to Subnet3 via Router2.


From a real-life perspective, here's a common problem that occurs when IPs are statically assigned with incorrect information.
Scenario:
1) SysA has an IP address with the correct NetworkID for Subnet1
2) SysB is incorrectly assigned an IP address in Subnet3


Result:
SysA will not be able to communicate with SysB.
- TCP/IP identifies the two IP addresses with different network IDs
- TCP/IP sends the traffic through the default gateway instead of directly to SysB


Similarly, SysB will not able to communicate with any other devices.
- TCP/IP identifies any traffic to other devices on Subnet1 as having a different network ID
- SysB will try to send the traffic through the default gateway


purpose of broadcast id?
A broadcast transmission sends traffic to all devices in the same subnet. For example, if SysA sends traffic with the broadcast IP as the destination IP address, all devices on Subnet1 receive the traffic. Routers do not pass (most) broadcasts so a broadcast transmission from SysA will not reach computers on Subnet2 or Subnet3.


Hope this helps.

Rosco2382

@Darril as I am starting to study for the Network+, what is the purpose of a broadcast. Maybe give an example so that i could better understand it. Also do you have any tips in doing subnetting? I feel I have a good understanding of it, but I'm doing the binary conversions of it and it just seems a tad bit tedious. I imagine with anything in math there are shortcuts. I just can't seem to figure it out.

Darril

Rosco2382 wrote: »

what is the purpose of a broadcast. Maybe give an example so that i could better understand it. Also do you have any tips in doing subnetting?

The purpose of a broadcast is to send traffic from one device to all devices on a network. In contrast, unicast sends traffic from one device to one device.

Samo3411 mentioned ARP requests which is an example of a broadcast usage.

Imagine Subnet1 has 200 clients and Subnet3 has 400 clients

TCP/IP starts with source and destination IP addresses.
Source: 192.168.1.5 (from Subnet1)
Destination: 10.80.1.4 (to Subnet3)

Once the traffic is on the same network (Subnet3), TCP/IP needs the destination media access control (MAC) address. The Address Resolution Protocol (ARP) sends out a broadcast request to all the devices on the network asking if they have the IP address of 10.80.1.4. The system with this address responds with its MAC address.

Only one data packet is sent out, which limits traffic on the network. Hubs and switches pass broadcasts so all devices connected on the network with a hub or a switch receive the broadcast.

On subnetting, this thread mentioned some good sites: http://www.techexams.net/forums/network/89866-new-needs-help.html

Yes, binary conversions can be tedious and yes, there are shortcuts. Once you learn how to do it and burn it into your neurons with repetition, the shortcuts typically appear to people naturally. I believe some of the sites quoted in that thread show some shortcuts too.

Good luck.

rrvm04

ALL ARE EXPLAINED VERY WELL each topic is understandable for each person in different ways but finally all are same that depends upon the understand.

BlueRoze

If you want some great Classful and VSLM subnetting books Google, "IPv4 Addressing and Subnetting Workbook version 2.1" and "VSLM Workbook IPv4 Version 2.3" That will take you right to the PDFs of the workbooks. They show you multiple methods and have some practice worksheets of the basic binary conversions. The VSLM one is really good, though probably above Net+ level. You can also find subnetting shortcut charts, but you will have to make sure they come with a good site that explains how they work. I don't have a good refernce for that one (the one I know of was taught in a class), so you'll have to search around and find one that works for you.