The Packet's Journey

 Software switching is significantly slower than switching done in hardware. Packets are hardware switched whenever possible. ip_input process consults the routing table and ARP table to obtain next-hop's routers IP address, outgoing interface and MAC address. Then it overwrites the destination MAC address with the next-hop router's and the the source with MAC address with the outgoing L3 interface, decrements the IP TTL, recomputes the IP header checksum and delivers the packet to the next-hop router. RIB - Routing information Base - This is built from the info obtained from dynamic routing protocols, directly connected and static routes. CEF is Cisco proprietary and was developed to keep up with evolving networks. It has been the default on most Cisco platforms that doing switching using general CPU since 1990's/ CEF is the default switching used by all Cisco platforms that use ACIS and NPU;s for high packet throughput.  General purpose CPU's on software and hardware ...

  Packets must be routed when devices are on different networks. Next-hop IP address is identified  by a static entry, default gateway or routing protocol Device looks for next hop IP address in the ARP table and uses the MAC address from the next-hop IP as the destination MAC address.  Next-hop router receives the packet based on the destination MAC address then analyzes the destination IP address, finds its the appropriate entry in the routing table, looks for the outbound interface then finds the destination MAC address looking to see if it needs to be routed further. The router then changes the source MAC address to the MAC address of the router's outbound interface while also changing the destination MAC address to the destination device or next-hop router. This process continues on and on as needed to get the packet from the source device to the destination device With either IPv4 or IPv6 an IP address mus be assigned to an interface for a router or L3 switch to rou...

 Ports can be manually configured as access ports with the command switchport mode access. switchport access (vlan-id/vlan name) associates a specific VLAN to that port     IE:          SW1# config t          SW1(config) # vlan 99          SW1 (config-vlan) # name Guests           SW1 (config-vlan) # Interface gi1/0/15           SW1 (config-if) # switchport mode access           SW1 (config-if) # switchport access vlan 99           Trunk ports can carry mulitple VLANS.  Trunk ports are used when need to connect multiple VLANS to another switch, a router or firewall using one port. (Think router on a stick) Trunking using the 802.1Q tag to encapsulate the packet and assign to the correct VLAN To setup a trunking port use command switchport mode trunk Use command show interface...

Network - provides connectivity between devices. Almost everything is based on TCP/IP in a network. (TCP - Transmission Control Protocol, IP- Internet Protocol) TCP/IP is based on the concept of Open Systems Interconnection or the OSI Model which is composed of 7 layers. 7 Layers: Application - Interface for receiving and Sending Data Presentation - Formatting of data and encryption Session - Tracking of packets Transport - End-to-End communication between devices Network - Logical addressing and routing of packets Data - hardware addressing Physical - Media type and connector When sending data across the network starts at layer 7 moves down the OSI model then transmits across the network to its destination and moves back up from layer 1 to layer 7. *Troubleshooting should always start at Layer 1 and move up the OSI model. (Most issues that I have observed working in an ISP reside on Layer 1 or Layer 2) Chapter 1 reinforces the concepts relate to how a network device forwards traffic f...