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2. A Class B Network Case Connected: An Internet Encyclopedia
2. A Class B Network Case

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Prev: 1. A Class A Network Case
Next: 3. A Class C Network Case (illustrating non-contiguous subnet bits)

2. A Class B Network Case

2. A Class B Network Case

For this case, assume that the requesting host is on class B network 128.99.0.0, has address 128.99.4.123, that there is a gateway at 128.99.4.62, and that a 6-bit wide subnet field is in use, that is, the address mask is 255.255.252.0.

The host sends the ICMP request to 255.255.255.255:

         Source address:          128.99.4.123
         Destination address:     255.255.255.255
         Protocol:                ICMP = 1
         Type:                    Address Mask Request = AM1
         Code:                    0
         Mask:                    0
The gateway can then respond directly to the requesting host.
         Source address:          128.99.4.62
         Destination address:     128.99.4.123
         Protocol:                ICMP = 1
         Type:                    Address Mask Reply = AM2
         Code:                    0
         Mask:                    255.255.252.0
In the diskless workstation case the host sends:
         Source address:          0.0.0.0
         Destination address:     255.255.255.255
         Protocol:                ICMP = 1
         Type:                    Address Mask Request = AM1
         Code:                    0
         Mask:                    0
128.99.4.62 will hear the datagram, and should respond with this datagram:
         Source address:          128.99.4.62
         Destination address:     255.255.255.255
         Protocol:                ICMP = 1
         Type:                    Address Mask Reply = AM2
         Code:                    0
         Mask:                    255.255.252.0
If broadcasting is not allowed 128.99.4.123 sends:
         Source address:          128.99.4.123
         Destination address:     128.99.4.62
         Protocol:                ICMP = 1
         Type:                    Address Mask Request = AM1
         Code:                    0
         Mask:                    0
128.99.4.62 should respond exactly as in the previous case.
         Source address:          128.99.4.62
         Destination address:     128.99.4.123
         Protocol:                ICMP = 1
         Type:                    Address Mask Reply = AM2
         Code:                    0
         Mask:                    255.255.252.0


Next: 3. A Class C Network Case (illustrating non-contiguous subnet bits)

Connected: An Internet Encyclopedia
2. A Class B Network Case

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