Subneting

tomsolomon

OK can somebody explain this to me in laymans terms....
Lets say I have two seperate network segments each with their own switch, and I wanted to assign individual IP addresses to each subnet group, subnet A being 172.16.8.x/24, and subnet B being 172.16.9.x/24.
Would the subnet mask be 255.255.255.0 or 255.255.0.0???
And why?
Also the suffix "/24" does this refer to the number of bits allocated to identifying the network?
:huh::huh::huh::huh:

debitcardmayhem

Wiki is my friend , it takes too long to type so for
IP addresses look here
and Subnet Mask here

Edit: then if you can't understand call us again

DVardysShadow

tomsolomon wrote: »

OK can somebody explain this to me in laymans terms....
Lets say I have two seperate network segments each with their own switch, and I wanted to assign individual IP addresses to each subnet group, subnet A being 172.16.8.x/24, and subnet B being 172.16.9.x/24.
Would the subnet mask be 255.255.255.0 or 255.255.0.0???
And why?
Also the suffix "/24" does this refer to the number of bits allocated to identifying the network?
:huh::huh::huh::huh:

Subnetting purely depends on IP addresses and subnet masks. If you have a link between your switches, you can have machines on both subnets on either switch and the subnets will just work.

You are correct that the subnet mask suffix /24 is the number of bits to identify the network - which means that the subnet mask is 255.255.255.0 ie 11111111 11111111 11111111 00000000 in binary. If you used /23 ie 255.255.254.0 [unusual but possible] you would have a larger subnet which would include both your proposed subnets.

Why do you need separate subnets? Just because you have 2 switches, this does not force you to separate them.

tomsolomon

DVardysShadow wrote: »

Subnetting purely depends on IP addresses and subnet masks. If you have a link between your switches, you can have machines on both subnets on either switch and the subnets will just work.

You are correct that the subnet mask suffix /24 is the number of bits to identify the network - which means that the subnet mask is 255.255.255.0 ie 11111111 11111111 11111111 00000000 in binary. If you used /23 ie 255.255.254.0 [unusual but possible] you would have a larger subnet which would include both your proposed subnets.

Why do you need separate subnets? Just because you have 2 switches, this does not force you to separate them.

I have read about this somewhere, reserving the first few addresses in the fourth octet, to assign to network devices. Wouldn't this limit the network to 256 nodes?
Also would a multi switch network need a router to handle the routing table or would DHCP suffice?

Ximian

tomsolomon wrote: »

OK can somebody explain this to me in laymans terms....
Lets say I have two seperate network segments each with their own switch, and I wanted to assign individual IP addresses to each subnet group, subnet A being 172.16.8.x/24, and subnet B being 172.16.9.x/24.
Would the subnet mask be 255.255.255.0 or 255.255.0.0???
And why?
Also the suffix "/24" does this refer to the number of bits allocated to identifying the network?
:huh::huh::huh::huh:

You could have the subnet mask as either /16 or /24 (255.255.0.0 or 255.255.255.0 respectively). But by default the 172.16.x.x network range has a 255.255.0.0 subnet mask
/24 is known as CIDR notation but it means that with IPv4, which has 32 bit IP Addressing, 24 bits are allocated to the subnet which means that you can have more subnets but less hosts. It leaves you with 8 bits for the host portion: 2^8=256-2 = 254 hosts (the network address and broadcast addresses [0, 255] are subtracted from the total )

If you were to use the 172.16.x.x address range with a subnet mask of 255.255.0.0 (/16) you could have 2^16=65536-2 = 65534 hosts on one large subnet.

The choice is yours, do you want more subnets or more hosts, the smaller the subnet mask the larger the amount of hosts, the larger the subnet mask the larger the number of subnets and smaller the number of hosts.

The main thing to remember is that all your hosts connected to the same switch should have the same subnet mask assigned.

tomsolomon

Ximian wrote: »

You could have the subnet mask as either /16 or /24 (255.255.0.0 or 255.255.255.0 respectively). But by default the 172.16.x.x network range has a 255.255.0.0 subnet mask
/24 is known as CIDR notation but it means that with IPv4, which has 32 bit IP Addressing, 24 bits are allocated to the subnet which means that you can have more subnets but less hosts. It leaves you with 8 bits for the host portion: 2^8=256-2 = 254 hosts (the network address and broadcast addresses [0, 255] are subtracted from the total )

If you were to use the 172.16.x.x address range with a subnet mask of 255.255.0.0 (/16) you could have 2^16=65536-2 = 65534 hosts on one large subnet.

The choice is yours, do you want more subnets or more hosts, the smaller the subnet mask the larger the amount of hosts, the larger the subnet mask the larger the number of subnets and smaller the number of hosts.

The main thing to remember is that all your hosts connected to the same switch should have the same subnet mask assigned.

I got it......:P
With a subnet mask of 255.255.0.0 the first two octets denote the network address and the second two octets would be used for host addresses....

Ximian

tomsolomon wrote: »

I have read about this somewhere, reserving the first few addresses in the fourth octet, to assign to network devices. Wouldn't this limit the network to 256 nodes?
Also would a multi switch network need a router to handle the routing table or would DHCP suffice?

You'd only need a router if you had a need for one, if you had separate networks with different network addresses, possibly for security reasons, a WAN. If you require a small network then switches can suffice.

What would you like to do? How many hosts do you need to connect?
If you could provide some details on the network and requirements we might be able to assist

tomsolomon

I used the two switch as an example so I could get a better understanding without complicating things too much.
There is a office and a conference room adjoining, and two training rooms seperated by a corridor, up to 30 machines at any one time in each training room, three in the office, and I was contemplating wireless access for the conference room.

DVardysShadow

tomsolomon wrote: »

Also would a multi switch network need a router to handle the routing table or would DHCP suffice?

When you have switches, these are totally transparent to IP addresses. Switches do not know about IP addresses at all. So you need a DHCP server - which is often but not always the router for a complete network.

Routers are then used to connect your network to another network. You can have several switches on your network and you don't need to worry about them if you have a router and a DHCP server - as long as the DHCP server puts everything on the same subnet and the router knows the subnet, you can plug anything else in anywhere on your network.

All the switches do for you is allow you to couple many machines to your network and to extend the network beyond the reach of a single ethernet segment.

tomsolomon

DVardysShadow wrote: »

When you have switches, these are totally transparent to IP addresses. Switches do not know about IP addresses at all. So you need a DHCP server - which is often but not always the router for a complete network.

Routers are then used to connect your network to another network. You can have several switches on your network and you don't need to worry about them if you have a router and a DHCP server - as long as the DHCP server puts everything on the same subnet and the router knows the subnet, you can plug anything else in anywhere on your network.

All the switches do for you is allow you to couple many machines to your network and to extend the network beyond the reach of a single ethernet segment.

So a router would negate the need for switches and hubs could be used in their place?

DVardysShadow

Ximian wrote: »

You could have the subnet mask as either /16 or /24 (255.255.0.0 or 255.255.255.0 respectively). But by default the 172.16.x.x network range has a 255.255.0.0 subnet mask
/24 is known as CIDR notation but it means that with IPv4, which has 32 bit IP Addressing, 24 bits are allocated to the subnet which means that you can have more subnets but less hosts. It leaves you with 8 bits for the host portion: 2^8=256-2 = 254 hosts (the network address and broadcast addresses [0, 255] are subtracted from the total )

If you were to use the 172.16.x.x address range with a subnet mask of 255.255.0.0 (/16) you could have 2^16=65536-2 = 65534 hosts on one large subnet.

The choice is yours, do you want more subnets or more hosts, the smaller the subnet mask the larger the amount of hosts, the larger the subnet mask the larger the number of subnets and smaller the number of hosts.

The main thing to remember is that all your hosts connected to the same switch should have the same subnet mask assigned.

More on the subnet mask for the 172.16.x.x networks. In the old days, this was a class B network and the network mask 255.255.0.0 was mandatory. But with the introduction of 'classless' IP routing, the standard subnet masks for IP ranges are purely historical.

Concerning the second highlighted statement, this is misleading. You can have several subnets which are totally unrelated on a network. For example 10.0.1.0/24 and 172.16.7.0/16. There are sometimes reasons to do this [which I won't go into]. Since switches are completely oblivious to IP addresses, it does not matter how the subnets are mixed across switches. And you can have one machine with 2 network interfaces - one on each subnet configured as a private router if you want.

One subnet on a network will work fine with a default DHCP setup - the second subnet can also be DHCP - but you need a configurable DHCP server and you'll need to get involved with MAC addresses.

But for the OP's situation, just wire it all up with switches to distribute to all the places you want to reach. Then forget about the switches and make it all the same subnet with 1 DHCP server and 1 router