Source IP Address - Contains a 32-bit binary value that represents the source IP address of the packet.ĭestination IP Address - Contains a 32-bit binary value that represents the destination IP address of the packet. Common values include ICMP (1), TCP (6), and UDP (17). Protocol - This 8-bit binary value indicates the data payload type that the packet is carrying, which enables the network layer to pass the data to the appropriate upper-layer protocol.

On the other hand the layer 2 frame header (ethernet or whatever) has the MAC address of the source (which would be the original host at this point) and the MAC address of the next router the packet is to be sent to. The traceroute command uses this field to identify the routers used between the source and destination. The IP header has the source and destination IP address for the packet, which is used to get the packet across the internet. If the TTL field decrements to zero, the router discards the packet and sends an Internet Control Message Protocol (ICMP) Time Exceeded message to the source IP address. The packet sender sets the initial time-to-live (TTL) value and is decreased by one each time the packet is processed by a router, or hop. It is specified in seconds but is commonly referred to as hop count. Time-to-Live (TTL) - Contains an 8-bit binary value that is used to limit the lifetime of a packet.