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3. A Class C Network Case (illustrating non-contiguous subnet bits) Connected: An Internet Encyclopedia
3. A Class C Network Case (illustrating non-contiguous subnet bits)

Up: Connected: An Internet Encyclopedia
Up: Requests For Comments
Up: RFC 950
Up: Appendix II. Examples
Prev: 2. A Class B Network Case
Next: Appendix III. Glossary

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

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

For this case, assume that the requesting host is on class C network 192.1.127.0, has address 192.1.127.19, that there is a gateway at 192.1.127.50, and that on network an 3-bit subnet field is in use (01011000), that is, the address mask is 255.255.255.88.

The host sends the ICMP request to 255.255.255.255:

         Source address:          192.1.127.19
         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:          192.1.127.50
         Destination address:     192.1.127.19
         Protocol:                ICMP = 1
         Type:                    Address Mask Reply = AM2
         Code:                    0
         Mask:                    255.255.255.88.
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
192.1.127.50 will hear the datagram, and should respond with this datagram:
         Source address:          192.1.127.50
         Destination address:     255.255.255.255
         Protocol:                ICMP = 1
         Type:                    Address Mask Reply = AM2
         Code:                    0
         Mask:                    255.255.255.88.
If broadcasting is not allowed 192.1.127.19 sends:
         Source address:          192.1.127.19
         Destination address:     192.1.127.50
         Protocol:                ICMP = 1
         Type:                    Address Mask Request = AM1
         Code:                    0
         Mask:                    0
192.1.127.50 should respond exactly as in the previous case.
         Source address:          192.1.127.50
         Destination address:     192.1.127.19
         Protocol:                ICMP = 1
         Type:                    Address Mask Reply = AM2
         Code:                    0
         Mask:                    255.255.255.88


Next: Appendix III. Glossary

Connected: An Internet Encyclopedia
3. A Class C Network Case (illustrating non-contiguous subnet bits)

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