IP (Internet Protocol) Version 4 for CCNA R&S

Why some places used routable IP for their internal infrastructure? for example 22.x.x.x or 100.x.x.x.x

Hello Francisco

In general, it is best practice not to use routable IP addresses on the internal infrastructure. However, it is possible to use these addresses internally. In many cases you can get away with it and it will work fine. However, if a host on the inside is trying to reach a routable IP address of a web server on the Internet, for example, but that IP address also exists on the inside of the network, such a request will go to the inside address and not to the web server on the Internet.

This is the primary reason for the segregation of IP addresses as routable and private.

I hope this has been helpful!

Laz

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@lagapidis
As you said , " Routing protocols such as EIGRP, OSPF and RIP communicate and use only up to layer 3 encapsulation." .

But in IP header it shows that protocol is OSPF , But in Layer 4 header u can see that there is a OSPF header it self , is not it a Layer-4 ??

Hello Narad

You could say that OSPF operates at Layer 4, since in Wireshark you can see that it is operating on top of Layer 3. However, when we refer to “Layer 4” we are referring specifically to the Transport Layer, where protocols such as TCP and UDP live, and where ports are used to separate sessions and to determine to which application each arriving segment belongs. In this sense, because there is no TCP or UDP applied at all, OSPF is not considered a Layer 4 protocol. It simply functions on top of IP.

I hope this has been helpful!

Laz

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Hi Rene ,
i have a question please , in order to find what exactly is the network address and the broadcast address all is needed is to changed to host bits to 1 or 0 , and that will give me the right addresses no matter which ip address i am trying to check?

also if its right is it the same with public addresses as well? do public addresses have a network and a broadcast address as well?

i am sorry for all the questions just trying to understand , thank you so much

Hello Vladimir

Yes, that is correct, no matter what IP address you are checking. This is the same for public or private addresses, the mechanisms are the same. Take a look at this NetworkLessons Note on IPv4 network and broadcast addresses for more detailed information.

I hope this has been helpful!

Laz

Hi Laz ,

thank you very much , that was very helpful.

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Hello,

How to get the following Private IP range, whether I can only memorize them?

⦁ Class A: 10.0.0.0 – 10.255.255.255
⦁ Class B: 172.16.0.0 – 172.31.255.255
⦁ Class C: 192.168.0.0 – 192.168.255.255

Hello Chun

These are ranges of IP addresses that are defined by a standard and should simply be memorized. More information about the standard can be found at this NetworkLessons note about IPv4 Private IP address ranges.

I hope this has been helpful!

Laz

Oh I see, Thank your honest replay

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Hi Rene,
I tried to ping 127.0.0.1 127.0.0.2 127.0.0.3 1270.0.254, I got loopback message. So, am I right to infer that address range from 127.0.0.1 to 127.255.255.254 are addresses reserved for loopback and 127.0.0.0 is the network address and 127.255.255.255 is for network broadcast ?
If I am wrong, please correct me.

Thanks and Best regards,
Charles

Hello Charles

The 127.0.0.0/8 address range is called the Internal host loopback address range. Addresses of this form are used to refer to the host itself. If you were to ping any of these addresses on any network device, you should get a response. This is because these addresses refer to the local host. This address range is defined in full in section 3.2.1.3.g of RFC 1122.

In practice, any ping to an IP address of 127.0.0.1 all the way up to 127.255.255.254 will have a response from the local host assuming that the IP protocol stack (the interface itself that is) is up and running. Now theoretically, the 127.0.0.0 and 127.255.255.255 addresses are reserved for network and broadcast respectively, however, in practice, these have no meaning in the context of the local loopback. Indeed I tried pinging 127.0.0.0 on my PC and I got a general failure message. Similarly, I got no response from 127.255.255.255. So these addresses in reality are meaningless in this context.

I hope this has been helpful!

Laz

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Hi Rene,
Thank you for possibility of discussion in connection to lesson material. Personally I am obtaining a big benefit from this blog. Your replay is comprehensive to question. Thank you.

Actually, I think about loopack addresses and realize that there is a wastage , is not? So many addresses dedicated to be loopback in its purpose in the situation when we have shortage of iPv4 addresses? I realize that dedicated loopback range would be standardized in the situation when shortage was not visible yet.

Hello Rafal

Yes, I agree with you! Setting aside the range of 127.0.0.0/8 means that you’re setting aside over 16 million addresses just for the host loopback address!! Remember that the IPv4 protocol was designed primarily in the early 1980s, so there was no way for engineers to foresee address exhaustion as a problem almost forty years later! So they set aside way too many addresses for loopback. There were other seemingly wasteful allocations as well, including the 240.0.0.0/4 which has been set aside for experimental use/future use.

They could change this definition to free up addresses, but I think they decided against it since IPv6 had already been designed in the late 1990s, and was expected to be rolled out sooner.

IPv6 has taken this wastage into account, and even though there are many more available addresses, the loopback address in IPv6 is a single address:

0:0:0:0:0:0:0:1/128 or ::1/128

This IPv6 loopback is defined in RFC 4291.

I hope this has been helpful!

Laz

Can I have explanation in subnetting . I have seen the difference of playing octets in class a b c. I observe that for class c only fourth octet is played while doing subnetting . I can see it has got host bits only in fourth octet. But when it comes to Class b they are host bits in both third and fourth octet. But only third octet is played in class b subnetting. Similarly in class a only second octet is played but they are host bits in both second, third and fourth

Hello Pavan

Take a look at this NetworkLessons course on subnetting.

There you will find all of the information you need to successfully understand the process. I suggest you begin with the following introduction, and as you go along, let us know of any additional questions or clarifications.

I hope this has been helpful!

Laz

Hello Team ,

Can you please help me to explain how exactly data is flow from application layer to physical layer in depth and please emphasis most in transport layer and network layer because in transport layer it work on port to Port basis and also advised why ip protocol is connectionless protocol .

Sorry to ask this silly question as i m revising my concepts again after long time . :blush:

Still don’t received any update .Please do needful

Best Regards
Shivam Chahal

Hello Shivam

Take a look at this NetworkLessons note about an example of communication between hosts in the same subnet and in different subnets. It describes the various layers and their operation. If you have any specific questions about this process, please let us know!

I hope this has been helpful!

Laz

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Hi Lagapide ,

What it means 254 host addresses per network .Is it mean 2^24 = Network .
I think 2^ 8 =256 network which will used 254 host address per network (private range for Class C ( 192.168.0.0-192.168.255.255 ) after replacing network address and broad case address .Please correct if i am wrong .

How many unique network will create in Class A , Class B and Class C private IP network ?

BR
Shivam

Hello Shivam

As stated in my post, Class C addresses have 24 bits for the network portion and 8 bits for the host portion. 2^8=256 is the number of host addresses you can have, but because we reserve the first and last value for network and broadcast addresses respectively, the number becomes 254.

Yes you are right, that means that we can have theoretically 2^24 Class C networks. However, there is a restriction. Notice that class C addresses always start with 110 at the beginning. Notice this again in the lesson:
image

That means that you can’t have 2^24 class C networks. The actual number is 2^21 because those first three bits must remain unchanged.

There are similar restrictions for Class A and B networks too, where the first bit in class A must be 0 and the first two bits in B must be 10. This can also be seen in the image above:

So how many unique networks can we have for each class?

  • Class A: 2^7 networks = 128
  • Class B: 2^14 networks = 16384
  • Class C: 2^21 networks = 2097152

I hope this has been helpful!

Laz