Subnetting question.

Hi I am new to Cisco. I have a assignment that requires to connect and configure devices on a topology in packet tracer but I am stuck on one instruction. hope someone could help?

it said "Use 10th class “C” private network to assign subnets for serial link with appropriate mask" . I am not sure what this means?

I know that :
Class A = 1 to 126
Class B = 128 to 191
Class C = 192 to 223

and private address blocks are:

10.0.0.0 /8 or 10.0.0.0 to 10.255.255.255
172.16.0.0 /12 or 172.16.0.0 to 172.31.255.255
192.168.0.0 /16 or 192.168.0.0 to 192.168.255.255

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Comments

clarson

What you need to know is the appropriate subnet mask for a serial link. What do you think that is?

txn41655

Class C subnet is 255.255.255.0 . But why does it say the "10th" ?

clarson

you should be able to find the "first" one.

and if you know the appropriate subnet mask for a serial link, you can find the rest.

txn41655

Thanks, but I'll have to ask my teacher, there are no reference of any ip address nor subnet address on this assignment.

OctalDump

I'll give you a hint. The first class B network is 128.0.0.0. Its netmask is 255.255.0.0. So the 2nd class b network is 128.1.0.0, then 128.2.0.0 etc.

That should get you far enough to work out what the 10th would be.

txn41655

Thanks for the hint ! Is this correct (Please correct me if I am wrong) ?? :

Class A Class = 0 to 126 subnet 255.0.0.0

1st Class A = 0.0.0.0
2nd Class A = 1.0.0.0
3rd Class A = 2.0.0.0
4th Class A = 3.0.0.0
5th Class A = 4.0.0.0
6th Class A = 5.0.0.0
7th Class A = 6.0.0.0
8th Class A = 7.0.0.0
9th Class A = 8.0.0.0
10th Class A = 9.0.0.0

Class B Class = 128 to 191 subnet 255.255.0.0

1st Class B = 128.0.0.0
2nd Class B = 128.1.0.0
3rd Class B = 128.2.0.0
4th Class B = 128.3.0.0
5th Class B = 128.4.0.0
6th Class B = 128.5.0.0
7th Class B = 128.6.0.0
8th Class B = 128.7.0.0
9th Class B = 128.8.0.0
10th Class B = 128.9.0.0

Class C Class = 192 to 223 subnet 255.255.255.0

1st Class C = 192.0.0.0
2nd Class C = 192.0.1.0
3rd Class C = 192.0.2.0
4th Class C = 192.0.3.0
5th Class C = 192.0.4.0
6th Class C = 192.0.5.0
7th Class C = 192.0.6.0
8th Class C = 192.0.7.0
9th Class C = 192.0.8.0
10th Class C = 192.0.9.0

txn41655

Use 10^th class “C” private network to assign subnets for serial link with appropriate mask :

1st Class C private network 192.168.0.0
2nd Class C private network 192.168.0.1
3rd Class C private network 192.168.0.2
4th Class C private network 192.168.0.3
5th Class C private network 192.168.0.4
6th Class C private network 192.168.0.5
7th Class C private network 192.168.0.6
8th Class C private network 192.168.0.7
9th Class C private network 192.168.0.8
10th Class C private network 192.168.0.9 ?

txn41655

1st Class C private network 192.168.0.0
2nd Class C private network 192.168.1.0
3rd Class C private network 192.168.2.0
4th Class C private network 192.168.3.0
5th Class C private network 192.168.4.0
6th Class C private network 192.168.5.0
7th Class C private network 192.168.6.0
8th Class C private network 192.168.7.0
9th Class C private network 192.168.8.0
10th Class C private network 192.168.9.0 ?

clarson

192.168.9.0 would be right if the appropriate subnet mask is /24

but, serial links are usually point to point networks. and point to point networks use a /30 subnet.
and, not all serial links are point to point so they will use something else other then a /30 subnet.

it all comes down to knowing what the "appropriate" subnet mask is.

redgunner

If the question means from the reserved then it would be

Class A - The 10th subnet would be 19.0.0.0
Class B - The 10th subnet would be 172.25.0.0
Class C - The 10th subnet would be 192.168.9.0

You always minus 1 when you are asked that question (10 minus 1) and just add that to the appropriate part of the Network Portion

OctalDump

txn41655 wrote: »

Use 10^th class “C” private network to assign subnets for serial link with appropriate mask :

1st Class C private network 192.168.0.0
2nd Class C private network 192.168.0.1
3rd Class C private network 192.168.0.2
4th Class C private network 192.168.0.3
5th Class C private network 192.168.0.4
6th Class C private network 192.168.0.5
7th Class C private network 192.168.0.6
8th Class C private network 192.168.0.7
9th Class C private network 192.168.0.8
10th Class C private network 192.168.0.9 ?

That would be my answer. This is based on the assumption that they are only asking you to use classful addressing, so no CIDR or classless addressing.

In the real world you tend to use classless addressing, which allows you to make your point to point serial links a /30 subnet (ie a subnet with just two usable host addresses).

txn41655

my instructor said is classful. Now in my topology I have a central router with 4 serial links, 2 lan links.

Should I assign this way? (Use 10th class “C” private network to assign subnets for serial link with appropriate mask ):
192.168.9.1 to the 1st serial link
192.168.9.2 to the 2nd serial link
192.168.9.3 to the 3rd serial link
192.168.9.4 to the 4th serial link

clarson

192.168.9.1 is a host address. it isn't a network address.

what you are looking to do is divide the 192.168.9.0 network into 6 segments. To do that you need to know how many hosts are required on each segment. such as if only two hosts are required on each segment, you could do:
192.168.9.0 1st
192.168.9.4 2nd
192.168.9.8 3rd
192.168.9.12
192.168.9.16
192.168.9.20

but if you need more hosts on a segment you'll need to make the segment(s) larger.

txn41655

correction, I have a central router with 5 serial links (to 5 other routers) , 2 lan links (to 2 switches). Do intermediary devices count as host?

clarson

that depends on how the device is configured. such as a 2950 switch with multiple vlans. the 2950 supports one switch virtual interface (svi). It can have an ip address or not.
if the svi isn't assigned an ip address, then none of the vlan networks have an ip address on the switch.
if the svi is assigned in ip address, then the vlan with the ip address has a host address on the switch. But, none of the other vlans do.
if you change the ip address of the svi from one vlan to another. Then the vlan that had the svi ip address loses a host address. And, the vlan that gets the svi gains a host ip address.

So, an intermediary device might count, might not. Basically, if the device is configured with an ip address on an interface, it counts for the network that the interface is attached.