Google has an IP address of 142.250.64.206. I found this out using nslookup.
Why is it class B and not class A? Isn't Google a huge network?
The whole A, B, C class system was obsoleted decades ago with the introduction of Classless Inter-Domain Routing (CIDR). https://www.findip-address.com/ shows 142.250.64.206 is part of a /24 CIDR block, not a /16 as the class B would've indicated (years ago).
Schools still teach this though, and I am not sure why. But you should know that when someone gives you an address and also says "it's a class C mask" or simply (and, technically, incorrectly) "it's a class C", the mask is /24. That's the only time in comes up in the real world.
Related
I was studying about Classful addressing with subnetting and Classless addressing but I am not able to clearly understand the difference/advantages between the two of them.
Suppose I have a company wants only 32 public IP addresses I can give them a Class C address with a subnet of 27 bits. Similarly I could give them a CIDR subnet to achieve the same result.
|What is my advantage in using CIDR?
| Why was CIDR required even after subnetting can achieve the same result?
| Shortcomings of subnetting with classful addresses.
Thanks in advance.
You are confusing a couple of concepts. Inter-Domain routing under network classes required that entire address class blocks be assigned to a single entity. There was no way to route inter-domain traffic except by class. You could subnet within a single entity, but you could not divide a classful block between entities.
All CIDR is doing is saying that the classes no longer exist, and you can break up what used to be a classful address block among different entities.
Network classes no longer exist, and they really are studied only for historical purposes. Learn how to subnet using CIDR first (become expert at it), then you can learn about network classes as a history lesson.
Class A starts with first bit 0
Class B starts with first two bits 10
Class C starts with first three bits 110
Class D starts with first four bits 1110
Class E starts with first four bits 1111
My friend, classful addressing is basically dividing the total ipV4 range into five classes :
Class A
Class B
Class C
Class D
Class E
whereas CIDR is based on concept of subnetting.
In your example , your company wants 32 public ip addresses. When we give them a class C address for example : 192.168.2.0 , their company will be reserved for whole ip addresses in range 192.168.2.1 - 192.168.2.254.But they only want 32 ip addresses which means 223 ip addresses will be wasted. This is the constraint of classful addressing . Now if we look at just subnetting , class c ip address has default subnet of 255.255.255.0 so if we divide the range of 192.168.2.0 in 6 subnets each containing 32 available ip addresses your problem is solved. But, if we take this example to higher level we will require CIDR. According to traditional subnetting, we can not combine the addresses from the networks 192.168.2.0 and 192.168.3.0 because the netmask for class C addresses is 255.255.255.0.However, using CIDR notation, we can combine these blocks by referencing this chunk as 192.168.2.0/23. This specifies that there are 23 bits used for the network portion that we are referring to. With this ,the 24th bit can be either 0 or 1 and it will still match, because the network block only cares about the first 23 digits.
CIDR allows us more control over addressing continuous blocks of IP addresses. This is much more useful than the subnetting we talked about originally . Your example only requires subnetting but if we require huge amount of addresses so that we may require to link class C address with class B portion , we will require CIDR.
IP Addresses have stayed the same. What has changed is "How devices can determine Network and Node part from an IP Address. With classful IP Address based processing, the number of bits assigned to network and host parts were fixed. For example when processing ip addresses using classes concept, the system will first determine the class of the IP Address and then use predetermined subnet mask to determine the network portion and host portion.
For class A first octet is network bit which allows 126 networks to be represented.
Due to restrictions on number of hosts and networks imposed by classes, you can define your own subtask mask which represent the network and host part of an IP address regardless which IP Address class you are using. The way that subnet mask is represented in text is called the "CIDR Notation".
Can anyone explain me, why is the subnet z seven hops away from the router D (and not 3 hops)? Which ones are counted? Please see picture below:
I believe the 'break' in the image means "any number of routers exist here."
I am currently studying for an IT exam, and looking into IP addressing. I have thus come across the following question:
For a given class C network 194.1.2.3, what is the network prefix?
I know this is a fairly simple, theoretical question, but I need to understand why. So far, I have the following working:
IPv4 applies dotted-decimal notation to divide the 32-bit address into four 8-bit fields (for readability).
Furthermore, the IP address space (not sure if right term) is divided into three classes (A, B, and C) to support networks of different sizes (classful addressing).
XXXX . XXXX . XXXX. XXXX
I also know the following:
Address Class A A(/8 prefixes)
Address Class B B(/16 prefixes)
Address Class C C(/24 prefixes)
I have thus concluded that 194.1.2 constitutes the network prefix of the given class C network, seeing that these make up the first 24 bytes.
Is this correct; and if so: Would the prefix for class A and class B networks be 194 and 194.2 respectively?
Thanks in advance!
Classful networking was deprecated over 20 years ago, and I don't understand why it is still taught since nothing uses it anymore.
The network class has noting to do with the network mask, but the classes have default masks.
Class A network addresses start with the first bit as 0, giving you
0.0.0.0 to 127.255.255.255 as the Class A address range. The
default mask for Class A networks is 255.0.0.0.
Class B network addresses start with the first two bits as 10,
giving you 128.0.0.0 to 191.255.255.255 as the Class B range. The
default mask for Class B networks is 255.255.0.0.
Class C network addresses start with the first three bits as 110,
giving you 192.0.0.0 to 223.255.255.255 as the Class C range. The
default mask for Class C addresses is 255.255.255.0.
Class D addresses start with the first four bits as 1110, giving
you the 224.0.0.0 to 239.255.255.255 as the Class D range. Class
D addresses are used for multicast, and multicast doesn't normally
use masks since multicast groups are subscribed to individually.
Class E addresses start with the first four bits as 1111, giving
you the 240.0.0.0 to 255.255.255.255 as the Class E range. Class
E addresses are reserved/experimental so they don't have a default
mask, except for the Limited Broadcast address of 255.255.255.255
which is a host address with the mask of 255.255.255.255.
I'm trying to make a list of all MAC addresses that are reserved, do not exist, should not be used, should only be used locally etc. (Just like the list of reserved IP-addresses on Wikipedia, but for MAC.) Basically I want to loop over all MAC-addresses from a switch and filter out the "real" ones.
This page suggests all addresses starting with 00-00-5E or 01-00-5E are reserved, but when I look them up it seems like 00-00-5E is also assigned to the Information Sciences Institute (part of a university in California).
So 2 questions:
1) Is there any place I can find a list of reserved MAC-adresses?
2) What's up with 00-00-5E? Is only part of that range reserved, or is there some reason they assigned it to ISI?
I was just looking into this myself recently. I believe that the IANA (which you refer to in one of your links) will give the most authoritative answer: IANA Ethernet Number Assignments
I don't think that this means that these addresses can never be used though. According to RFC5342, Section 2.1
"The 2**8 unicast identifiers from 00-00-5E-00-00-00 through 00-00-5E-00-00-FF are reserved and require IESG Ratification for allocation (see Section 5.1)."
So basically, it appears you need special permission from IESG (Internet Engineering Steering Group) to get an address in that range, which I suppose the ISI has obtained somehow.
Section 2.1 of RFC5342 deals with 48-Bit MAC Identifiers and OUIs, and it doesn't make any mention of any address ranges that are strictly forbidden or permanently reserved from what I've understood.
The following OUI are reserved as per RFC 5342:
OUI 01:00:5E:(00:00:00-7f:ff:ff) - Used for IPV4 Multicast and MLPS Multicast.
OUI 00:00:5E:(00:01:00 – 00:01:FF) - Used for Virtual Router Redundancy Protocol (VRRP) IPV4
OUI 00:00:5E:(00:02:00 – 00:02:FF) - Used for Virtual Router Redundancy Protocol (VRRP) IPV6
OUI 33:33:00 – 33:33:FF - Reserved for IPV6 Multicast
OUI CF:00:00 – CF:FF:FF - Reserved by IANA for PPP(Point to Point Protocol)
OUI 00:00:5E (00:00:00 - 00:00:FF) - Requires IESG Ratification for allocation.
Was looking into this myself.. I know it's been a while since the post was active.. but I found these to be ok to use locally:
x2-xx-xx-xx-xx-xx
x6-xx-xx-xx-xx-xx
xA-xx-xx-xx-xx-xx
xE-xx-xx-xx-xx-xx
Source: https://honeywellaidc.force.com/supportppr/s/article/Locally-Administered-MAC-addresses
The registration authority for MAC addresses is the IEEE. It hands out OUIs (Organizationally Unique Identifiers), which give you a three byte prefix, and 2^24 addresses within it, for a fee (currently 2 995USD). You also get the rights to the corresponding multicasts, which have the prefix with the lowest bit of the first byte set. For instance, 00:80:C2 is allocated to the IEEE 802.1 committee, which uses 01:08:C2:00:00:00 for Spanning tree.
So, there isn't really a list of reserved addresses. There is a list of OUIs that have been allocated, unless the buyer has paid (a lot) extra for privacy. You can use any address that has the local bit set freely. A tiny fraction of multicast addresses have a significant meaning because heavyweights like IEEE, Cisco, IANA assign meanings to them. From the IEEE registration point of view, there is no particular significance to these blocks (except possibly to those it has allocated to itself).
Now, how did the 01-00-5E range end up allocated to the Information Sciences Institute? The simple
answer is that they paid for it. So, really the question should be 'how did the Internet get to use part of the range allocated to ISI?'. The answer is that the IANA used to be run from an office in ISI: specifically IANA was the legendary Jon Postel
Bottom line: you are on a bit of a fool's errand. You can distinguish local addresses and multicast addresses, and make some attempt to tie up allocated unicast addresses to vendor blocks. And you can probably do a bit more with well-known multicast addresses but only by tracking down individudal vendor's documentation (IANA is obviously an important one but only definitive for 1 of the 2^22 available blocks). One of the best places to start is probably the Wireshark codebase.
When I use traceroute, I often see abbreviations in the hostnames along the route, such as "ge", "so", "ic", "gw", "bb" etc. I can guess "bb" means backbone.
Does anyone know what any these strings abbreviate, or know any other common abbreviations?
These are ISO-3166-1 Alpha2 geographical domain id's converted to lower case.
ge - Georgia
gw - Guinea-Bisseau
so - Somalia
bb - Barbados
ic - old code for Iceland?
Just look for ISO-3166 for the complete list of country codes. And RFC 1700 for the geo domain list.
Can you please provide the output from one of your traceroutes?
Hostnames using components such as bb for backbone and gw for gateway tend to put those towards the start of a hostname, e.g. bb1.toto.com.au or gw2.wtf.co.uk.
This follows a naming convention of more specfic to less specific elements in the name as you traverse from left to right.
Geographical domains are, almost always, at the end of the hostname.
The examples you provided makes me think it's not about country codes.
I guess it's just what you thought: ISP network admins using shorcut when naming their servers.
bb = backbone
gw = gateway
ic = interconnect?
ge = ?
so = stackoverflow? :)
They're unlikely to be country codes. When you're in charge of a large scale network, you come up with naming schemes that make sense to you, mixing geographical and functional notations, but without being too verbose since it's too wasteful to type.
gw, for example, always stands for gateway. ge typically means "gateway external", i.e. a border gateway to a "friendly" network. ix stands for interchange.
Unless they are the top level domain name (eg "foo.bb" rather than "bb.example.net"), then they are choosen by the organisation that owns that domain name, remember if you own a domain name, you own all subdomains. In that case, you can call it whatever you want. There's no specification and people call it many different things.
There are many 2 level top level domains, one for each country. E.g. .fr for France. More info: http://en.wikipedia.org/wiki/CcTLD
Short version; Country codes
Likely not totally correct, but...
A comlete listing of country codes is at
http://www.iso.org/iso/country_codes/iso_3166_code_lists/english_country_names_and_code_elements.htm
Other Top Level Domains (TLD) are at:
http://www.icann.org/en/registries/listing.html
actually, "ge" most likely stands for "Gigabit Ethernet", and it's quite common for the ports on routers to be named after the interface name.
Hence the first Gig-E port on a router will quite often have a hostname that includes "ge0" or similar.
You'll also see:
"fa" for "Fast Ethernet" (on Cisco routers)
"s0" for "Serial" (i.e. E1 or T1 ports)
"lo0" for "Loopback"
so = sonet, pos = packet over sonet
xe= ten gigabit
ge= gigabit