Subnet

Subnet, panji subnetwork, ni kugaŵika kwa IP network. Updated by RFC 6918. Kachitiro ka kugaŵa netiweki mu ma netiweki ghaŵiri panji kujumpha apo kukuchemeka subnetting.

Makompyuta agho ghali mu subnet yimoza ghali na gulu lakuyana la most-significant bits mu ma IP address ghawo. Ichi chikupangiska kuti IP address igaŵike mu vigaŵa viŵiri: network number panji routing prefix, na rest field panji host identifier. Rest field ni kakanyisidwe ka host panji netiweki interface yinyake.

Routing prefix yingalembeka nga ni adiresi yakwamba ya netiweki, yakulembeka mu Classless Inter-Domain Routing (CIDR) notation, kulondezgapo chizindikiro cha slash ('/'), na kumalira na utali wa ma bit gha prefix. Mwachiyelezgero,  ni prefix ya Internet Protocol version 4 netiweki yakwambira pa adiresi iyo yaperekeka, na ma bit 24 ghakupimika chifukwa cha network prefix, ndipo ma bit 8 ghakukhalapo ghakusungikira host addressing. Ma adiresi kufuma pa  kufika pa  ngali mu netiweki iyi, na  nga ni subnet broadcast address. Ma IPv6 adiresi  ni gulu likuru la ma adiresi na ma adiresi ghakukwana 296, ndipo lili na 32-bit routing prefix.

Ku IPv4, netiweki yingamanyikwaso na subnet mask panji netmask yake, iyo ni bitmask iyo, para yagwiriskika ntchito na bitwise AND operation pa IP adiresi yiliyose mu netiweki, yikupereka routing prefix. Ma subnet mask ghakuwoneskekaso mu dot-decimal notation nga ni IP adiresi. Mwachiyelezgero, prefix ya  yingaŵa na subnet mask ya .

Traffic yikusinthaniskika pakati pa ma subnet kwizira mu ma router para routing prefixes ya adiresi yakufumira na adiresi yakuyako yapambana. Router yikugwira ntchito nga ni mphaka ya masamu panji ya thupi pakati pa ma subnet.

Vyandulo vya kugaŵa netiweki mu ma subnet (subnetting) vikusintha kuyana na umo netiweki yikugwilira ntchito. Mu Internet, pakugwiriskira ntchito CIDR, na mu mawupu ghakurughakuru, kugaŵira makora malo gha ma adiresi nkhwakukhumbikwa. Subnetting yingawovwiraso kuti routing yiŵe yakuluta panthazi panji kuŵa na vyandulo mu network management para ma subnet ghakulamulirika na vigaŵa vyakupambana mu wupu ukuru. Ma subnet ghanganozgeka mu nthowa ya hierarchical architecture, kugaŵa malo gha ma adiresi gha netiweki ya wupu mu nthowa ya thiriyi (tree-like routing structure) panji vinyake nga ni meshes.

Kupereka adiresi na kusamiska traffic (Network addressing and routing) thumb|400px|Fundo ya kugaŵa malo gha adiresi ya IPv4 ya 200.100.10.0/24, iyo yili na ma adiresi 256, mu malo ghaŵiri ghachoko, kwali ni 200.100.10.0/25 na 200.100.10.128/25 na ma adiresi 128 pa ilo lililose Makompyuta agho ghali mu netiweki ya IP ghali na adiresi yimoza panji kujumpha ya network address. Kanandi, adiresi iyi njapadera pa chipangizo chilichose ndipo yinganozgeka mwakuyana na network service na Dynamic Host Configuration Protocol (DHCP), panji na munthu uyo wakulaŵilira (administrator), panji na operating system pakugwiriskira ntchito stateless address autoconfiguration.

Adiresi yikugwira ntchito yakumanyiska host na kuyisanga pa netiweki mu destination routing. Nthowa yakumanyikwa chomene ya kupereka ma adiresi ni Internet Protocol version 4 (IPv4), kweni yakulondezgapo yake, IPv6, yayamba kugwiriskika ntchito chomene kufuma mu chaka cha 2006. IPv4 address yili na ma bit 32. IPv6 address yili na ma bit 128. Mu nthowa zose ziwiri izi, IP adiresi yili kugaŵika mu vigaŵa viŵiri, network prefix na host identifier. Ma host ghose pa subnet ghali na network prefix yakuyana. Prefix iyi yikutora ma bit ghakuzirwa chomene (most significant bits) gha adiresi. Chiŵerengero cha ma bit agho ghapikiwa mu prefix chikupambana pakati pa ma subnet, kuyana na network architecture. Host identifier ni kakanyisidwe kapadera ka malo (local identification) ndipo ni nambara ya host pa netiweki ya pamalo panji interface identifier.

Kugaŵika kwa ma adiresi uku kukuzomerezga kusamiska routing kwa ma IP packet mu ma netiweki ghanandi kwizira mu makompyuta ghapadera ghakuchemeka ma router, kuluta ku host iyo yikukhumbikwa para ma network prefix gha adiresi yakufumira na yakuyako yapambana, panji kutumizgika mwachindunji ku host pa netiweki ya pamalo para prefix zili zakuyana. Ma router ni mphaka za masamu panji za thupi pakati pa ma subnet ndipo ghakulaŵilira traffic pakati pawo. Subnet yiliyose yikuteŵetereka na router yimoza (default router) kweni mukati yingaŵa na vigaŵa vyanandi vya Ethernet ivyo vyakolekana na network switches.

Routing prefix ya adiresi yikumanyikwa na subnet mask, yakulembeka mu nthowa yakuyana na iyo yikugwiriskika ntchito pa ma IP adiresi. Mwachiyelezgero, subnet mask ya routing prefix iyo yili na ma bit 24 ghakuzirwa gha IPv4 adiresi yikulembeka nga ni .

Nthowa ya mazuŵa gano ya kulongosora network prefix ni CIDR notation, iyo yikugwiriskika ntchito ku IPv4 na IPv6. Yikuŵerenga chiŵerengero cha ma bit mu prefix na kusazgapo nambara iyo pa adiresi para palamulika chizindikiro cha 'slash' (/). Nthowa iyi yikambika na Classless Inter-Domain Routing (CIDR). Mu IPv6, iyi ndiyo nthowa yimoza pera yakuzomerezgeka kulongolera network panji routing prefixes.