2013年8月14日星期三

Subnetting Issue

Question:

I have two Pc's connected WS-C3750X-24T-L together. PC1 i configured 10.1.1.1/8 address and PC2 with 10.1.1.10/16 address. I feel it should not ping between this two systems because though the IP address may be same but the subnetmask is different. But it pings how can this ping.

Answer:

of course.
1) IP addresses and netmasks are all 32 bits binary values so
     10.1.1.1/8= 10.1.1.1 255.0.0.0
  10.1.1.1=  0000101000000010000000100000001
  255.0.0.0= 11111111000000000000000000000000
boolean AND is, T meaning True or 1 and F meaning False or 0
T AND T= T
T AND F= F
F AND T=F
F AND F= F

so if we do the bitwise AND between the IP address and the mask we get:
00001010000000000000000000000000 which is 10.0.0.0

The same operation is done on the destination address.

For futher information, please refer to  http://www.3anetwork.com/cisco-ws-c3750x-24t-s-price_p102.html

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