Device Information
This page explains the functions of various devices supported by Packet Tracer 3.
Router Functions:
. A router has multiple Ethernet and/or WAN ports.
. Each Ethernet port has a MAC address, an IP address, and a subnet mask.
. Each WAN port has an IP address and a WAN address.
. A router uses RIP version 2 to find routes to remote networks automatically.
. A router advertises all networks that its ports belong to, which is specified by the IP address and subnet mask. RIP version 2 supports VLSM.
. RIP keeps a routing table of remote networks. The routing table associates a network (network ID and subnet mask or network bits) to the port that the router is closest to the network.
. A router can have one default port.
. When a router receives a layer 3 unicast packet, it checks the TTL field to see if the packet is to be forwarded. If the TTL field is greater than 0, it is to be forwarded. Otherwise, the packet is dropped.
. If the packet is to be forwarded, it looks up its routing table to find the network that the packet's IP address belongs to.
. If the network is found, the router forwards the packet out to that port that is closest to that network.
. If the network is not found, the router forwards the packet to the default port.
. If a default port is not specified, the router drops the packet.
. When a router forwards a layer 3 packet, it changes the destination frame address to the next hop's layer 2 address. If the next hop is the destination PC, the destination frame address is changed to the destination PC's MAC address. The source frame address is changed to this router's outgoing port's layer 2 address.
. When a router receives a layer 2 broadcast frame, it drops the frame.
. A router also acts as a DHCP server for LANs that it connects to.
. When a PC or wireless PC, that connects to a port on a router, sends a DHCP request, the router send a DHCP reply back to the PC. The DHCP reply will contain information on what to assign the PC's IP address, subnet mask, and default gateway. The default gateway is the IP address of the port that the router receives the DHCP request. The subnet mask is the same as that port's. The IP address is next available IP address in this port's network. DHCP packets are not shown to the user.
Switch Functions:
. A switch has multiple ports.
. A switch uses STP to break loops in a switching network.
. A switch keeps a MAC table. The MAC table associates a MAC address to the port that the switch can use to reach the device with this MAC address.
. When a switch receives a layer 2 unicast frame, it looks up the frame's MAC address in its MAC table.
. If the MAC address is found, then it matches to a port, and the switch forwards the frame out to that port.
. If the MAC address is not found, then the switch forwards the frame to all except the incoming port.
. When a switch receives a layer 2 broadcast frame, it forwards the frame out to all except the incoming port.
. A switch can have multiple VLANs.
. Each port can be assigned to one VLAN.
. Frames cannot go across VLANs.
. Each port on the switch can be configured as a trunk port.
. Each VLAN can be assigned to multiple trunk ports.
. A trunk port can be used to send frames from and to VLANs that are assigned to it.
. When a switch sends a frame over a trunk port, it adds a tag to the frame specifying which VLAN the frame belongs to.
. When a switch receives a frame from a trunk port, it removes the tag that is on the frame, and uses the tag to determine the VLAN to send the frame out to.
Bridge Functions:
. A bridge has two ports.
. A bridge does not have VLAN or trunking functions.
. All other bridge functions are identical to switch functions.
Hub Functions:
. A hub has multiple ports.
. When a hub receives a packet, it forwards the packet to all except the incoming port.
. When a hub receives more than one packet at the same time, a collision occurs and both packets become corrupted.
Repeater Functions:
. A repeater has two ports.
. When a repeater receives a packet on one port, it forwards the packet to the other port.
. Collisions do not occur inside a repeater.
PC Functions:
. A PC has one port that has a MAC address and an IP address.
. A PC can send layer 3 unicast packets and layer 2 broadcast frames.
. A packet from a PC can come from any layer 3 to 7 protocols.
. When a PC sends a layer 2 unicast packet, it automatically sends an ARP request to get the MAC address of the destination PC. An ARP reply is sent back automatically. This ARP process is not shown to the user.
. When a PC receives a packet, it checks to see if the packet's MAC and IP addresses match its port's.
. If they match, the packet has arrived at its destination.
. If they do not match, the PC drops the packet.
. A PC can use DHCP to automatically assign IP address, subnet mask, and default gateway from a DHCP server (router).
Access Point Functions:
. An Access Point has a port and a wireless port.
. The port can be connected to another wired port.
. The wireless port can be associated to multiple wireless PCs.
. All Access Point functions are identical to hub functions.
Cloud Functions:
. A cloud has multiple borders.
. Each border is a WAN port that has an IP address and a WAN address.
. A cloud does not have a default port.
. All other cloud functions are identical to router functions.