Is the 3rd octet the "c class" of an IP address (thus also called "c block")
or
is an IP address a "c class" IP address if the first octet is assigned a numerical value from 192 to 223?
or do both possibilites exist depending on whether its the internet or a local network or something? Im interested in what it is on the web (obviously).
thx!
So if ip is 202.54.1.1-100 and subnet is 255.255.255.248 – all IP belongs to same provider or user.
Best solution is get hosting in different data center.
There are various classes of IP *addressing*.
A given *address*, though, doesn't belong to one class or another. It's simply *an* address.
A better term would be to refer to it as a "class C network".
A class C network is a group of 256 address (254 addressable hosts) where the first 3 octets are the same.
In the "olden days", a class C network was the smallest possible division of IP addresses that an organization could obtain. In the olden days they were generous. Need an IP address? Here's 254, need them or not!
1.2.3.4, 1.2.3.5, and 1.2.3.131 all belong to the same Class C network. 1.2.4.1 does not.
For an IP address to belong to a class C network isn't it necessary for the first octet to be assigned a "number" from 192 to 223?
Yes, but...
... that's just an artifact of the allocation scheme.
You have to understand where this "class" stuff comes from in the first place.
The allocation system was originally set-up by ARPA, then inherited by IANA.
The thought was that there would be some big companies or organizations (say, the U.S. military, or IBM) that would need a whole BUNCH of addresses. They got "class A" networks. A class A network has more than 16,000,000 addresses.
HALF of the total address space was reserved for Class A networks - for a total of only 127 possible class A networks!
Other sections of the possible address space are reserved for Class B networks, multicasting, and other misc. uses.
The 192...223 range was designated to be allocated to class C networks.
In common usage, though, ANY block of 256 addresses where the first three octets are the same are referred-to as a "Class C network".
I guess, I understand it, now. What bothered me a bit was that SEOs generally talk about "class C IP addresses". Calling pretty much everything a class C IP address, when technically it isn't a class C IP address.
But if I understood you correctly, if the first three octets are the same (no matter what the number of the first octet is), it's called a class C IP address in everyday internet language so to speak?
Classful networking is obsolete on the modern Internet. There is no longer any such thing as a class A/B/C network. The correct modern representation for what would have been referred to as a "Class B" prior to 1993 would be "a set of /16 addresses", under the Classless Inter-Domain Routing (CIDR) system
IMHO you should also read up on Classless Inter-Domain Routing if you want to understand this better...
What bothered me a bit was that SEOs generally talk about "class C IP addresses".
Ah.
For SEO purposes, as well as DNS redundancy purposes (or server redundancy, in general) this is a short-cut way of quickly determining if two IP addresses *might* be on the same server, and/or *might* belong to the same organization.
So, for example, if you have a bunch of websites, and you don't want others to know that they are under common control, the common advice is to "put them on different class C networks". Really, they mean "on seperate /24 networks".
A popular DNS diagnostic site will complain if your DNS servers are not on "separate class C networks".
Now, is this really good advice? Probably not. It's a quick approximation. However, do you think Google is so stupid as to not go the extra distance to check the CIDR allocation?
If you really want to give no indication of common control of multiple websites, you need to make sure the IP addresses are allocated to different companies.
A popular DNS diagnostic site will complain if your DNS servers are not on "separate class C networks".
O/T it even complains when they are on separate continents ;)
By /24 network, I assume oyu mean a network for which the first 3 octets share the same numbers? Is that it?
Now, is this really good advice? Probably not. It's a quick approximation. However, do you think Google is so stupid as to not go the extra distance to check the CIDR allocation?
My guess would be that Google (or other SEs) do go the distance to check that. But then again with their algos it always depends on a reward/risk ratio..they cant put every possible calculation in their algo, I assume because that could possibly slow down their search (and thus harm their websites usability). But, I assume in this case that would hardly make a difference, right?
On the other hand most SEOs..or well most "whitehat" SEOs mostly use this when analyzing other site's link profiles by using tools and all....but I do find it a bit silly to be honest, when I hear every beginner in the SEO field use expression such as "different c class ip addresses" when they have no clue what a c class ip address really is. Thats why I was trying to find out after all :-)
If you really want to give no indication of common control of multiple websites, you need to make sure the IP addresses are allocated to different companies.
Im into whitehat SEO and general online marketing, not really into blackhat SEO (though I stay away from the "ethics" tag when it comes to search engines..), but what do you mean by allocated to different companies?
Is this the same thing as saying allocated to different class C (or class A or class B) networks?
what do you mean by allocated to different companies?
Exactly that.
If you use dig or nslookup to do a DNS lookup on an IP address (actually, reverse the address and add "in-addr.arpa", so for 1.2.3.4, look-up 4.3.2.1.in-addr-arpa) you will see who owns the IP address.
So, if black-hat networked site #1 has an address belonging to ABC Hosting, you might have black-hat networked site #2 on an IP address belonging to XYZ Hosting.
Of course, IPs belonging to the same company is an unreliable indicator of common ownership of sites, as there's no standard rule for who might own the IP - it might be owned by you, your hosting company, a hosting reseller, a data center, or a backbone transport company.
But "same /24" isn't a reliable indicator either. Under CIDR, a /24 can be split between different companies.
So, both are simply AN indicator that the sites MIGHT be under common ownership. The more sites are involved in the "network" of sites, though, the more probable it is that they are under common ownership, and the harder it becomes to hide. Say, you have some other indicator, first - such as "they all link to each other", "they are look similar", etc.
Now, you've got 1,000 sites, all looking similar and all of the IPs belong to the same company. What are the chances of that happening by happenstance? Pretty slim. At a certain point, it becomes pretty difficult to hide. What do you do, hire 1,000 designers to come up with different looks, and open accounts with 1,000 hosting companies?
