The Offer

Toy Fixed Layout

The shortened fixed layout keeps only the fields this book needs.

highlighted = computed this step

This is a shortened teaching layout

The fixed strip keeps only the fields needed for this lesson: operation, hardware shape, transaction id, offered address, and client MAC.

fixed bytes=18\text{fixed bytes}=18
Toy fixed layoutThe toy DHCP OFFER-like fixed fields are decoded from exact bytes.Toy fixed layout144 bits / 18 bytes0x0201060012345678c0a80132001122334455byte 0byte 1byte 2byte 300000010000000010000011000000000byte 4byte 5byte 6byte 700010010001101000101011001111000byte 8byte 9byte 10byte 1111000000101010000000000100110010byte 12byte 13byte 14byte 1500000000000100010010001000110011byte 16byte 170100010001010101op2htype1hlen6hops0xid0x12345678yiaddr192.168.1.50chaddr0x001122334455(cont.)

Hardware shape is explicit

Hardware type 1 and hardware length 6 tell the toy parser how to read the client MAC.

1,61,6
Toy fixed layoutThe toy DHCP OFFER-like fixed fields are decoded from exact bytes.Toy fixed layout144 bits / 18 bytes0x0201060012345678c0a80132001122334455byte 0byte 1byte 2byte 300000010000000010000011000000000byte 4byte 5byte 6byte 700010010001101000101011001111000byte 8byte 9byte 10byte 1111000000101010000000000100110010byte 12byte 13byte 14byte 1500000000000100010010001000110011byte 16byte 170100010001010101op2htype1hlen6hops0xid0x12345678yiaddr192.168.1.50chaddr0x001122334455(cont.)

No relay hop here

The hops field is 0 in this pinned message.

hops=0\text{hops}=0
Toy fixed layoutThe toy DHCP OFFER-like fixed fields are decoded from exact bytes.Toy fixed layout144 bits / 18 bytes0x0201060012345678c0a80132001122334455byte 0byte 1byte 2byte 300000010000000010000011000000000byte 4byte 5byte 6byte 700010010001101000101011001111000byte 8byte 9byte 10byte 1111000000101010000000000100110010byte 12byte 13byte 14byte 1500000000000100010010001000110011byte 16byte 170100010001010101op2htype1hlen6hops0xid0x12345678yiaddr192.168.1.50chaddr0x001122334455(cont.)

Summary

These fixed bytes are enough to show one offer to one client before option bytes refine the meaning.

fixed fields=7\text{fixed fields}=7
Toy fixed layoutThe toy DHCP OFFER-like fixed fields are decoded from exact bytes.Toy fixed layout144 bits / 18 bytes0x0201060012345678c0a80132001122334455byte 0byte 1byte 2byte 300000010000000010000011000000000byte 4byte 5byte 6byte 700010010001101000101011001111000byte 8byte 9byte 10byte 1111000000101010000000000100110010byte 12byte 13byte 14byte 1500000000000100010010001000110011byte 16byte 170100010001010101op2htype1hlen6hops0xid0x12345678yiaddr192.168.1.50chaddr0x001122334455(cont.)