| 9.1 |  | Examining the Routing Table |
| 9.1.4 |  | Determining L2 and L3 addresses |

| While network layer addresses are used to get packets from source to destination, it is important to understand that a different type of address is used to get packets from one router to the next. For a packet to get from the source to the destination, both Layer 2 and Layer 3 addresses are used. As shown in Figure , at each interface, as the packet moves across the network, the routing table is examined and the router determines the next hop. The packet is then forwarded using the MAC address of that next hop. The IP source and destination headers do not change, at any time. The Layer 3 address is used to route the packet from the source network to the destination network. The source and destination IP addresses remain the same. The MAC address changes at each hop or router. A data-link layer address is necessary because delivery within the network is determined by the address in the Layer 2 frame header, not the Layer 3 packet header.
| Interactive Media Activity Drag and Drop: L2 and L3 Address After completing this activity, the student will be able to identify L2 and L3 addresses.
| Web Links Using the Extended ping and Extended
traceroute Commands http://www.cisco.com/en/US/tech/ tk826/tk365/ technologies_tech_ note09186a0080093f22.shtml