4.3.11
Intuition Ek-line pictureIPv4 ne hume lagbhag 4.3 billion addresses diye. Planet par phones logon se zyada hain. IPv6 kami ko fix karta hai 32-bit addresses se 128-bit addresses par jump karke — aur saath mein IPv4 ke messy hisse bhi clean up karta hai (NAT, broadcast storms, manual config).
WHY hai 2 32 Har bit ek independent on/off choice hai. n 2 n 2 32
2 32 = 4 , 294 , 967 , 296 ≈ 4.3 × 1 0 9
Yeh bohot bada lagta hai, lekin:
Kaafi ranges reserved hain (private, loopback, multicast), toh usable count chhoti hai.
Har internet-connected device ek chahta hai. Phones, laptops, cameras, fridges, cars (IoT) ⇒ tens of billions of devices.
128 bits ko 8 groups of 16 bits (= 8 "hextets") ke roop mein likha jaata hai, har group 4 hexadecimal digits ka, colons se separated.
8 groups × 4 hex digits 16 bits = 128 bits
WHY hexadecimal? Ek hex digit exactly 4 bits encode karta hai (16 = 2 4 128/4 = 32
Full example:
2001:0db8:0000:0000:0000:ff00:0042:8329
Dono apply karne par example par:
2001:db8::ff00:42:8329
:: do baar use kar sakta hoon space bachane ke liye"
Why it feels right: agar ek :: achha hai, toh do aur better hone chahiye — zyada compression!
Why it's wrong: :: ka matlab hai "jitne zero-groups chahiye utne fill karo 8 groups tak pahunchne ke liye." Do :: ke saath, parser nahi bata sakta ki har gap mein kitne zeros jaate hain. 2001::25de::cade ambiguous aur illegal hai.
Fix: :: sirf sabse lambi zero-run ke liye use karo; baaki explicitly likho.
Ek typical unicast IPv6 address 64-bit network prefix (kaun sa network) aur 64-bit interface ID (us par kaun sa device) mein split hota hai. Notation CIDR use karta hai: prefix/64.
64 bits network prefix 64 bits interface ID = 128 bits
WHY 64/64? 64-bit interface ID itna bada hai ki 48-bit MAC address (EUI-64) se derive kiya ja sake aur autoconfiguration (SLAAC) DHCP server ke bina kaam kar sake.
Feature
IPv4
IPv6
Address size
32 bits
128 bits
Notation
dotted decimal 192.168.0.1
colon-hex 2001:db8::1
Address count
2 32 2 128
Header size
variable (20–60 B)
fixed 40 bytes
Broadcast
yes
no (multicast/anycast use karta hai)
Address config
manual / DHCP
SLAAC (auto) + DHCPv6
Fragmentation
router ya host
sirf sending host
Checksum in header
yes
removed (L2/L4 par rely karta hai)
Security (IPSec)
optional
designed-in (originally mandatory)
NAT needed?
usually yes
usually no
Worked example Broadcast kyun nahi?Why this step matters: IPv4 broadcast (255.255.255.255) har host ko jagataa hai — wasteful "broadcast storms." IPv6 ise multicast (sirf subscribed group ko deliver karo) aur anycast (group mein se nearest ko deliver karo) se replace karta hai. Isse unnecessary traffic kam hoti hai.
Worked example Fixed 40-byte header kyun?Why this step matters: IPv4 ka variable header (Options ke saath) routers ko har packet par length fields parse karne par majboor karta tha. IPv6 ek fixed main header use karta hai plus optional extension headers jo uske baad chain hote hain. Routers un extensions ko skip karte hain jo unhe parwah nahi ⇒ faster forwarding.
Common mistake "IPv6 sirf IPv4 hai longer addresses ke saath"Why it feels right: headline change sach mein address length hai.
Why it's incomplete: IPv6 ne broadcast bhi remove kiya, header checksum bhi remove kiya, header size fix ki, fragmentation sirf host par move ki, aur autoconfiguration add ki. Yeh ek redesign hai, patch nahi.
Fix: table yaad rakho — paanch se zyada structural changes, sirf bade addresses nahi.
Worked example Example 3 — loopbackIPv4 loopback 127.0.0.1 IPv6 mein 0000:...:0001 = ::1 ban jaata hai. Kyun? 127 zero groups collapse hote hain, last group 1 hai.
Recall Feynman: ek 12-saal ke bacche ko explain karoSocho phone numbers sirf 4 digit ke hote — jald hi naye logon ke liye koi number nahi bachta. IPv6 "numbers" ko bahut lamba bana deta hai (itna lamba ki basically kabhi khatam nahi honge) aur inhe letters-aur-numbers (hex) aur colons se likhta hai. Yeh kuch purani aaadtein bhi phenko deta hai — jaise building mein sabko chillana (broadcast) — aur sirf unse baat karta hai jo sunna chahte hain.
Mnemonic Format yaad rakho"8 groups, 4 hex, 128 in the box; double-colon once, zeros it drops."
8 groups × 4 hex digits = 128 bits.
:: ek baar, sabse lambi zero run khaata hai.
Ek IPv6 address mein kitne bits hote hain? 128 bits.
Total kitne IPv6 addresses exist karte hain? 2 128 ≈ 3.4 × 1 0 38
IPv4 se kitne guna zyada addresses hain? 2 96 2 128 / 2 32
IPv6 address kaise likha jaata hai? 8 groups of 4 hexadecimal digits colons se separated.
IPv6 mein hexadecimal kyun? 1 hex digit = 4 bits, toh 32 hex digits = 128 bits; bit-aligned aur compact.
:: ka kya matlab hai aur kitni baar appear ho sakta hai?Consecutive all-zero groups ki ek run replace karta hai; sirf ek baar allowed hai (warna ambiguous).
IPv6 main header ka size kya hai? Fixed 40 bytes.
Kya IPv6 mein broadcast hota hai? Nahi — yeh multicast aur anycast use karta hai.
IPv6 mein IPv4 ke manual/DHCP config ki jagah kya aaya? SLAAC (stateless address autoconfiguration), plus DHCPv6.
IPv6 mein fragment kaun kar sakta hai? Sirf sending host (routers nahi kar sakte).
IPv6 mein header checksum kyun remove kiya gaya? Routing speed badhane ke liye; integrity L2 (link) aur L4 (TCP/UDP) handle karte hain.
Typical IPv6 prefix/interface split kya hai? 64-bit network prefix + 64-bit interface ID.
IPv6 loopback address kya hai? ::1.
fe80::/10 range ka kya matlab hai?Link-local addresses (auto, non-routable).
IPv4 count 2 32 32 independent binary choices 2 32
Hexadecimal 4 bits per digit
Ambiguous illegal address
64-bit prefix plus 64-bit interface ID
