Ukutholwa kwe-MTU yendlela nge-VPN: usayizi kanye negebe le-ICMP

Ithuneli liqeda ukuxhawulana kwalo, izicelo ezincane ziyabuya, kanti ukudluliswa kokuqala okukhulu kuyama. Leli phethini likhomba ku-MTU yendlela kudala ngaphambi kokuba likhombe kumthamo wokusebenza. Yonke ikhonkco endleleni inciphisa usayizi wephakethe, futhi ukufakwa kwephakethe kusebenzisa ingxenye yaleyo mvume kumakhanda angaphandle, ngakho iphakethe langaphakathi kufanele libe lincane kunalokho indlela eluhlaza engakusikisela. Ukwehluleka kuthule, futhi yikho okukwenza kubize ukuxilongwa.

I-MTU yendlela ikala ini ngempela

I-MTU yendlela iyikhonkco elincane kakhulu le-MTU endleleni phakathi kwamakhasimende amabili, hhayi i-MTU ephrintiwe kusixhumi sangaphakathi sakho. Inani langaphakathi yindawo lapho isilinganiso siqala khona, futhi indlela inquma lapho kumele iphele khona. Yikho ithuneli elifanayo lingasebenza kunethiwekhi yokufinyelela eyodwa futhi lime kwelinye: indlela yashintsha, hhayi ukulungiselelwa. Ukukala kanye bese ucabanga kuyo yonke indawo yiphutha eligcina le nkinga iphila.

Ethunelini, inombolo ebalulekile yi-MTU yangaphakathi, okuyimvume yendlela yangaphandle isusa lokho okusetshenziswa ukufakwa kwephakethe. I-WireGuard yengeza ikhanda le-IP langaphandle nekanda le-UDP; ezinye izindlela zokuthutha zengeza ezazo. Beka usayizi wangaphakathi uphakeme kakhulu futhi yonke iphakethe losayizi ophelele lizodinga ukuhlukaniswa okungase kungaze kwenzeke.

Kungani ithuneli linciphisa iphakethe elisebenzisekayo

Uma isixhumi sethuneli sigcina i-MTU yekhonkco lomzimba, yonke iphakethe enkulu incike ekutheni othile ongezansi uzimisele ukuyihlukanisa. I-IPv4 iyivumela ngokomgomo, kodwa umzila otshelwe ukuthi ungahlukanisi ubuyisela iphutha esikhundleni salokho. Imizila ye-IPv6 ayihlukanisi nhlobo ekudlulisweni, ngakho ukulungiselelwa okufanayo kuziphatha ngendlela ehlukile kuye ngomndeni wamakheli. Noma kunjalo, umthumeli akafundi lutho kuze kube khona okubika emuva.

Umphumela ongokoqobo usayizi ongena ekuxhawulaneni kodwa ungene emthwalweni. I-TLS ClientHello noma umbuzo we-DNS mncane ngokwanele ukuba uwele indlela encishisiwe ungathintwanga, kuyilapho ukudluliswa okukhulu kungenjalo. Ngakho izimpawu zihlangana ezizungeze imisebenzi ethile hhayi amakhasimende athile.

Ukutholwa kusebenza kuphela lapho impendulo ifika

Ukutholwa kwe-IPv4 kuncike kubhithi le-don't-fragment: umzila ongakwazi ukudlulisela iphakethe ubuyisela i-ICMP fragmentation-needed nekanda le-MTU lesinyathelo esilandelayo, futhi umthumeli wehlisa isilinganiso sakhe. I-IPv6 isebenzisa imilayezo ye-Packet Too Big esikhundleni salokho, ngoba imizila ayihlukanisi ekudlulisweni. Zombili izindlela zicabanga ukuthi umlayezo uzothola indlela ebuyela kumthumeli, ngethuneli nangale kwanoma iyiphi ifayela lomlilo endleleni yokubuya. Lapho leso sicabango sehluleka khona, umthumeli uqhubeka ezama usayizi indlela engakwazi ukuwuthwala.

Ifayela lomlilo elivumela i-echo request ne-echo reply alivumanga ngempela lezo zinhlobo zamaphutha. I-ICMP ingumndeni, futhi amalungu abalulekile lapha amaphutha, hhayi ipheya le-echo. Hlola inqubomgomo yethrafikhi yokulawula kuzo zombili iziphetho zethuneli nasezindleni eziphakathi kwazo, futhi landela isiqondiso esisekelwayo sepulatifomu esikhundleni sokuvumela zonke izinhlobo ze-ICMP kuyo yonke indawo.

Ukuhlungwa okufanayo kungaba ngaphakathi kwethuneli. Uma indlela yangaphakathi ilahla iphutha kodwa indlela yangaphandle iyithwala, umthumeli angase azivumelanise nomkhawulo othrafikhi efakwe ephaketheni angakaze awubone ngempela.

Hlola indlela esikhundleni sokuqagela inombolo

Gcina indawo ekuyiwa kuyo, inethiwekhi yokufinyelela kanye nethuneli kumi, bese ushintsha kuphela usayizi wephakethe. Isivivinyo se-don't-fragment esihlulekayo ngesikhombo se-MTU sikunikeza umkhawulo wesinyathelo esilandelayo; phinda kuze kudlule usayizi othile, futhi urekhode kokubili usayizi nomndeni wamakheli.

ping -M do -s 1400 10.60.20.10
ping -M do -s 1300 10.60.20.10
ping -6 -M do -s 1300 2001:db8::10

I-ping engenayo ayifakazeli ukuthi izingxenye zosayizi ophelele zohlelo lokusebenza lwangempela ziyangena, ngakho phinda isivivinyo ngokudluliswa okwehluleka ngempela. Qhathanisa isivivinyo esikhulu kunazo zonke esisebenzile ne-MTU yethuneli oyilungiselele, futhi ugcine lezo zinombolo ezimbili zihlukene emanothini akho. Uma zehluka cishe ngekhanda elilodwa, uthole isengezo sokufakwa kwephakethe hhayi iphutha.

I-PLPMTUD, echazwe ku-RFC 4821, ihlola iya phezulu futhi isebenzisa iziqinisekiso zokuthutha esikhundleni sokuthemba amaphutha alethiwe. Iyasiza ezindleni ezihlunga i-ICMP, kodwa ukusekelwa kuyehluka ngesitaki nangohlelo lokusebenza. Ukugeleza kwe-TCP kungase kululame ngokwako kuyilapho uhlelo lwe-UDP olunosayizi odlulele wedatha luhluleka njalo.

Khetha inani futhi urekhode izizathu

Ukwenza i-MTU yethuneli ibe ncane kuyisifo kanye nokulungiswa okusemthethweni ngasikhathi sinye uma usuyazi indlela. Akuthathi indawo yokwazi ukuthi iyiphi indlela naluphi ubuchwepheshe bempendulo obuhilelekile, ngoba inani elilungiselelwe ikhonkco leselula lizoba lincane ngokungadingekile kuxhumano lwefayibha. Rekhoda usayizi okhethiwe, isivivinyo esiwufakazelayo kanye nesinyathelo sokuhoxisa.

Indlela ye-IPv4 ichazwe ku-RFC 1191 kanti isiqondiso sokupakisha se-IPv6 siku-RFC 8201; ukusho kokubili kuvimbela unjiniyela olandelayo ekuphinde athole leso sicabango. Uma ukudluliswa kusama kusayizi oyikhethile, yeka ukwehlisa inombolo bese ubheka isendlalelo esilandelayo. Indlela ehluleka kuwo wonke usayizi akuyona inkinga ye-MTU.