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TH1: My 1: 192.168.1.70 Netmask: 255.255.255.192My 2:
192.168.1.80 Netmask: 255.255.255.192
Kt qu: Cho 2 my PING nhau Kt qu Ping OK
TH2: My 1: 192.168.1.70 Netmask: 255.255.255.192My 2:
192.168.1.180 Netmask: 255.255.255.192
Kt qu: Cho 2 my ping nhau Kt qu Ping Khng c (V 2 IP ny khc
mng).
TH3: My 1: 192.168.1.62 Netmask: 255.255.255.192My 2:
192.168.1.128 Netmask: 255.255.255.192
Kt qu:My 1 khng t c IP v My 2 cng vy.
Ti sao vy? Cho bn kt lun nh.
Xong bi LAB
HNG DN CHI TIT C TH TNH NHANH
Khi tnh ton IP, chia Subnet th chng ta thng p dng cng thc tnh
ton.
Cng thc tnh l: 2^n v 2^h2(2^m - 2)
- tnh tng s Subnet c c sau khi chia ta dng cng thc 2^n, trong n
l sbit mn chia Subnet
trong Octet (Mn lm Network ID).
tnh tng s Host/Subnet ta dng cng thc 2^h-2, trong h l tng s bit
cn li dng lm Host sau khi
mn. Ta phi tr 2 v cn ba ch Subnet ID v Broadcast.Ni s s qua cch
tnh truyn thng nh vy thi, gichng ta tm hiu cch nhm nhanh bng cch m
lng
tay nh.
PHNG PHP CHIA SUBNET BNG CCH M LNG NGN TAYu tin cc bn xe bn tay
tri ra v m theo hnh
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Cc bn bn tay chng ta c tt c 14 lng tay, mi lng tay tng trng cho
1 bit nh.
m 2, 4, 8, 16, 32, 64, 128, 256, 512, 1024, 2048, 4096, 8192,
16384
m i m li cho thuc i nh cc bn.
- tnh tng slng Subnet ID c c sau khi chia, ta m sbit mn lm
Subnet ID trong Octet l ra.
Mn 3 bit th m 2, 4, 8 mn 4 bit th m 2, 4, 8, 16 gi tr ca bit m
sau cng chnh l tng s Subnet ID
Sau khi c chia ra.
V d: 10.10.0.0/13mn 5 bitm 2, 4, 8, 16, 32 vy mng ny c 32
Subnet.
- tnh bc nhy trong mi Subnet id. Ta m s bit cn li dng lm Host
trong ring Octet . Gi tr ca
bit c m sau cng cng l gi tr ca bc nhy trong Octet .
V d: 172.35.0.0/19. Tc l a ch lp B smn 3 bit Octet th 3 lm
Subnet ID. Dng phngphp m ta
c 2, 4, 8 3 bit mn ri, vy tng s Subnet ID l 8. Ta bit trong
Octet th3 sau khi cho mn 3 bit lm Net
ID th cn li 5 bit lm Host, vy ta m 2, 4, 8, 16, 32 5 bit ri, gi
trl 32, v cng chnh l bc nhy ca
Subnet ID
Thxem no:
Ta c tng cng 8 Subnet ID vi bc nhy l 32.
- tnh a ch Broadcast ca mt Subnet ID ta ly Subnet ID k tip gim
1.
V d: tnh Broadcast ca Subnet id 172.35.64.0/19, ta ly Subnet
id
K tip l 172.35.96.0/19 gim 1 = 172.35.95.255/19 y chnh l
broadcast ca Subnet ID 172.35.64.0
- tnh s Host trong mt Subnet, ta m ton b s bit Host cn li trong
Subnet v ly gi trbit sau cng
tr 2
Lu : l khng phn bit Octet. Nhc li, ta ly gi tr ca bit c m sau
cng tr2 ta c s Host trong
Subnet ID c th xi.
Trong v d Subnet 172.35.64.0/19, ta nhn bit ton b s bit dng lm
Host cn li l 13.
Ta m 2, 4, 8, 16, 32, 64, 128, 256, 512, 1024, 2048, 4096, 8192
13 bit ri ok S Host trong mng s
l 8192 - 2 = 8190. V sao tr 2, v ta phi tr ba ch Subnet ID v
Broadcast.
Hay n gin hn c th nhn thy l s Host c thxi c trong dy:
172.35.64.1/19 172.35.95.254/19 v ng thi n cng lt gia 2 Subnet
id v Broadcast.
Lu : Phng php m t2 khng c dng tnh tng s gi tr ca 1 octet chy t 0
255. Hay ni
cch khc l khng c dng tnh tng gi tr ca 1 dy bit nh 10101101. tnh
tng s gi tr ca dy
trn ta phi m t 1, cng cc gi tr c bit 1 vi nhau.
- 172.35.0.0/19- 172.35.32.0/19
- 172.35.64.0/19
- 172.35.96.0/19
- 172.35.128.0/19- 172.35.160.0/19
- 172.35.192.0/19
- 172.35.224.0/19
