cisco

• Primary functions and features of a router:

  • A router connects one network to another network
  • Responsible for the delivery of packets across different networks
• When source and destination IP addresses are on different networks, the Ethernet frame must be sent to a router
• Routers determine the best path to the destination and forward traffic to the next router along that path
• Routers are responsible for routing traffic between networks
• Routers are essentially specialized computers with components like CPU, memory, and storage
• Cisco devices use the Cisco Internetwork Operating System (IOS) as the system software
• Router memory is classified as volatile or non-volatile
• Primary functions of a router:

  • Determine the best path to send packets
  • Forward packets toward their destination
• Routers support three packet-forwarding mechanisms:

  • Process switching
  • Fast switching
  • Cisco Express Forwarding (CEF)
• Process switching:

  • Forwards packets to the control plane where the CPU matches the destination address with an entry in its routing table
  • Slow and rarely implemented in modern networks
• Fast switching:

  • Uses a fast-switching cache to store next-hop information
  • Packet is forwarded to the control plane where the CPU searches for a match in the cache
  • If not found, it is process-switched and forwarded to the exit interface
• Cisco Express Forwarding (CEF):

  • Builds a Forwarding Information Base (FIB) and an adjacency table
  • Table entries are change-triggered, not packet-triggered
  • Preferred Cisco IOS packet-forwarding mechanism
• FIB and adjacency tables are change-triggered and contain all the information a router needs for forwarding a packet after network convergence
• FIB contains pre-computed reverse lookups and next hop information for routes, including interface and Layer 2 details
• Cisco Express Forwarding is the fastest forwarding mechanism and the preferred choice on Cisco routers
• Network devices and end users connect to a network using wired Ethernet or wireless connections
• LANs in the figure show examples of how users and network devices connect to networks
• Home Office devices connect:

  • Laptops and tablets wirelessly to a home router
  • Network printer using an Ethernet cable to the switch port on the home router
  • Home router to the service provider cable modem using an Ethernet cable
  • Cable modem to the Internet service provider (ISP) network
• Branch site devices connect:

  • Corporate resources to Layer 2 switches using Ethernet cables
  • Desktop PCs and VoIP phones to Layer 2 switches using Ethernet cables
  • Laptops and smartphones wirelessly to wireless access points (WAPs)
  • WAPs to switches using Ethernet cables
  • Layer 2 switches to an Ethernet interface on the edge router using Ethernet cables
• Central site devices connect:

  • Desktop PCs and VoIP phones to Layer 2 switches using Ethernet cables
  • Layer 2 switches redundantly to multilayer Layer 3 switches using Ethernet fiber-optic cables
  • Layer 3 multilayer switches to an Ethernet interface on the edge router using Ethernet cables
  • Corporate website server to the edge router interface using an Ethernet cable
  • Edge router to a WAN service provider (SP) and ISP for backup purposes
• Hosts in Branch and Central LANs connect to the network infrastructure using a Layer 2 switch
• Default gateways are essential for network access and devices must be configured with:

  • IP address
  • Subnet mask
  • Default gateway
• Network documentation should include:

  • Device names
  • Interfaces used in the design
  • IP addresses, subnet masks, and default gateway addresses
• Console access for infrastructure devices requires:

  • Console cable (RJ-45-to-DB-9 serial cable or USB serial cable)
  • Terminal emulation software (Tera Term, PuTTY, HyperTerminal)
• Network infrastructure devices require IP addresses for remote management using Telnet, SSH, HTTP, or HTTPS
• Switches use a switched virtual interface (SVI) for configuring IP address information
• Basic router settings configuration tasks include:

  • Naming the device
  • Securing management access
  • Configuring a banner for legal notification of unauthorized access