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

This topic is to discuss the following lesson:

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Great insight on IPs, still struggling with the subject but this is well helpfull moving forward. Thank you, great we’ll.

Hi i am Ali. I read this article . it is very helpful for beginners in Cisco IP Routing.

Thanks Again

Hi Vusi,

Any particular topic you have trouble with? I can always create a blogpost for it.

Rene

Hi Rene,
I want to know that if we use subnetting for an IP address. Then also we have to leave a network and broadcast IP for our network?

Hi Vicky,

Each subnet always has a network + broadcast address so you need to keep that in mind when you are assigning IP addresses to hosts. The first IP address in the subnet is always the network address, the last one the broadcast address.

Rene

Rene,

Thanks! I think topic like this, VLSM and CIDR scare some CCNA students, but you write and show them of a nice way.

When you have a free time, please fix this sentence below… It’s a little detail

I just explained to you “1that 92.168.1.1 is a class C”

and about the video, you wrote in whiteboard 172.16.0.0 - “172.32.0.0”, I think it was test our attention :smiley:

Abraço

Hi Gabriel,

Thank you, i just fixed this error. About the video…that’s a bad monday morning error :stuck_out_tongue: I’ll re-record this one hehe.

Rene

Hi Rene,

I do know that 127.0.0.1 ~ 127.255.255.254 are the loopback IP addresses for most modern operating systems and we could use these IP addresses to refer to our own computer. But isn’t 127.0.0.1 enough?!?! why a wide range? why from 127.0.0.1 to 127.255.255.254?

Hi Hussein,

Back in the 80s we only used class A,B and C ranges so that’s probably why they reserved an entire class A range for the loopback. We didn’t have VLSM back then and the idea of running out of IP addresses probably never occured to anyone.

Rene

Hi Rene,

So why we don’t use range from class B or C ? and why we have only ::1/128 loopback address in ipv6

Hi Hussein,

I think nobody back then gave it much thought…the RFC that specifies the private range is from 1986 or so.

For IPv6 they probably did give it some more thought so there’s only 1 loopback address :slight_smile:

Rene

Thanks Rene I’ve got the idea.

Hi Rene,

What do the address 127.0.0.0 and 127.255.255.255 mean?
I thought all the IPs that start with 127 can be used to refer our PC. When I ping them, I get the below messages.

C:\Users\VijayKumar>ping 127.0.0.0

Pinging 127.0.0.0 with 32 bytes of data:
General failure.
General failure.
General failure.
General failure.

Ping statistics for 127.0.0.0:
Packets: Sent = 4, Received = 0, Lost = 4 (100% loss),

C:\Users\VijayKumar>
C:\Users\VijayKumar>
C:\Users\VijayKumar>ping 127.255.255.255

Pinging 127.255.255.255 with 32 bytes of data:
Request timed out.
Request timed out.
Request timed out.
Request timed out.

Ping statistics for 127.255.255.255:
Packets: Sent = 4, Received = 0, Lost = 4 (100% loss),

C:\Users\VijayKumar>

Are they reserved for network and broadcast addresses even though we won’t be using them anywhere?

Cheers,
Vj

Hi VJ,

The 127.0.0.0/8 range is used for loopback addresses.

127.0.0.0 is the network address and 127.255.255.255 is the broadcast address.

You can ping any address in the 127.0.0.0/8 range except those two.

Rene

Thank you

Hi Rene,

What about the Range 0.0.0.0 ~0.255.255.255/8 ?? Please give a short defination of CIDR and VLSM . Is both are some ??

br//
zaman

Hi Zaman,

0.0.0.0/8 - Addresses in this block refer to source hosts on “this” network. Address 0.0.0.0/32 may be used as a source address for this host on this network; the addresses within 0.0.0.0/8 may be used to refer to specified hosts on this network ([RFC1122], Section 3.2.1.3).

VLSM = Variable Length Subnet Mask. This means we let go of the class A/B/C subnet masks and use whatever masks we want to use.

The CIDR notation means we write down subnet masks like /24 instead of 255.255.255.0.

Rene

Hi Rene,

Actually I have a MAC OS and I don’t know why but only the loopback address 127.0.0.1 successful respond to a ping command. 127.0.0.2 for instance I got error message.

Thanks,
Best regards,
Fernando

Hi Fernando,

I’m not a MAC user but it seems that by default, only 127.0.0.1 is used as a loopback address on MAC OS.

Take a look at this post on Stack Overflow, they explain how to enable the entire range:

Rene