IPV4 Adres Çeşitleri

Giriş
IPV4 adresleri 3 sınıfta toplanır. Açıklaması şöyle.

IP addresses can be divided into categories.

• Routable on the public Internet.
• Routable on private networks but not on the public Internet
• Not routable at all.

0.0.0.0 Adresi
Açıklaması şöyle. Ağdaki paketleri dinlersek sadece boot aşamasında DHCP isteğinde bulunan bilgisayarlar tarafından source adres alanında kullanıldığı görülebilir.

This host on this network. MUST NOT be sent, except as a source address as part of an initialization procedure by which the host learns its own IP address.

Loopback Adres - Geri Dönüş
Not : 127.0.0.0 rezerve adrestir. Açıklaması şöyle

In IPv4, the first address of a subnet is reserved for...unclear reasons, really, but most likely because very long ago it used to be the "broadcast" address. (Later, the last address became the standard broadcast address.)

Bunların farklı olduğunu görmek için şöyle yaparız. Aslında çok önemli değil, çünkü 127.0.0.1 ve 127.0.0.2 adreslerinde aynı porta farklı sunucular zaten çalıştırılabiliyor

docker run -d --rm --hostname node1 --name node1 -p 127.0.0.0:8080:8080 alpine \
  sh -c "apk add --update darkhttpd; mkdir /srv; hostname > /srv/index.html; darkhttpd /srv --port 8080"

docker run -d --rm --hostname node2 --name node2 -p 127.0.0.1:8080:8080 alpine \
  sh -c "apk add --update darkhttpd; mkdir /srv; hostname > /srv/index.html; darkhttpd /srv --port 8080"

$ curl 127.0.0.0:8080
node1
$ curl 127.0.0.1:8080
node2

127.0.0.1 - 127.255.255.254 arası loopback içindir. Açıklaması şöyle.

127.0.0.0/8 - This block is assigned for use as the Internet host loopback address. A datagram sent by a higher level protocol to an address anywhere within this block should loop back inside the host. This is ordinarily implemented using only 127.0.0.1/32 for loopback, but no addresses within this block should ever appear on any network anywhere [RFC1700, page 5].

Ağı dinlersek 127 ile başlayan paketleri görmememiz gerekir çünkü bu paketlerin bilgisayar dışına çıkmaz. Açıklaması şöyle.

A 127.X.X.X address is attached to a loopback interface. Such an interface has no underlying layer attached (i.e. it is not attached to a link layer). The packet is processed and responded to in the Internet layer. So there's really no way for this packet to reach anything outside the host.

Private Adres
 Private Source veya Destination Ip adresleri internete çıkamaz. Açıklaması şöyle.

The Internet Assigned Numbers Authority (IANA) has reserved the following three blocks of the IP address space for private internets:

Açıklaması şöyle.

Private IPv4 addresses allow you to run a network without applying for public IP addresses at your regional registry. Since IPv4 addresses have run out it's the only way to set up a new network or expand an existing one.

Private Ip Adresleri şöyle.

10.0.0.0       - 10.255.255.255   /8
172.16.0.0   - 172.31.255.255   /12
192.168.0.0 - 192.168.255.255 /16

Aynı tablo şöyledir.

10.0.0.0        -   10.255.255.255  (10/8 prefix)
172.16.0.0      -   172.31.255.255  (172.16/12 prefix)
192.168.0.0     -   192.168.255.255 (192.168/16 prefix)

Neden 192 İle Başlayan Private Adresler Daha Yaygın Kullanılıyor
Soru şöyle. Cevabı 192 ile başlayan adresler genellikle yeterli büyüklük sunuyor.

RFC 1918 “Address Allocation for Private Internets” specifies 10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16 as private addresses suitable for unrestricted private internal use. Many home networks use the 192.168.1.0/24 address space.

Since 10.0.0.0/8 is a larger address space than 192.168.0.0/16, it would make sense to use 10.0.0.0/8 since there can be more IPs per network.

Why isn't 10.0.0.0/8 commonly used instead?

Multicast Adres
[224.0.0.0 - 239.255.255.255] aralığı kullanılabilir. Açıklaması şöyle. 

224.0.0.0/24 is the range assigned by IANA for local multicast - Local Network Control Block.

Bu blokta bazı adresler kullanılamaz.

Örnek

Açıklaması şöyle

The range of addresses between 224.0.0.0 and 224.0.0.255, inclusive, is reserved for the use of routing protocols and other low-level topology discovery or maintenance protocols, such as gateway discovery and group membership reporting. Multicast routers should not forward any multicast datagram with destination addresses in this range, regardless of its TTL.

Shared Adres
Shared Address Space şöyle. Carrier Grade NAT için kullanılır.

100.64.0.0/10

Açıklaması şöyle. Yani kendi router'ımdan IPv4 adresime bakarsam 100.A.B.C şeklinde bir adrese sahip olduğumu görürüm. 

That block of addresses is reserved for service providers to be able to do NAT in such a way that it doesn't conflict with the normal private address space.

Açıklaması şöyle.

Shared Address Space is similar to [RFC1918] private address space in that it is not globally routable address space and can be used by multiple pieces of equipment. However, Shared Address Space has limitations in its use that the current [RFC1918] private address space does not have. In particular, Shared Address Space can only be used in Service Provider networks or on routing equipment that is able to do address translation across router interfaces when the addresses are identical on two different interfaces.

IETF Blocked Address
whois komutu ise ile şöyle yaparız.

$> whois -h whois.ripe.net 243.25.203.20

Çıktı olarak şunu alırız.

inetnum:        243.0.0.0 - 243.255.255.255
netname:        IETF-RESERVED-ADDRESS-BLOCK
descr:          IPv4 address block reserved by the IETF
remarks:        ------------------------------------------------------
remarks:
remarks:        This address block is reserved by the IETF
remarks:
remarks:        You can find more information on the IANA registry page:
remarks:        http://www.iana.org/assignments/ipv4-address-space
remarks:
remarks:        -----------------------------------------------------