CCNA Chapter 8

• What is the title of Chapter 8? Network Layer
• The network layer provides services to allow end devices to exchange data.
• IP version 4 (IPv4) and IP version 6 (IPv6) are the principle network layer communication protocols.
• The network layer performs four basic operations:

  • Addressing end devices
  • Encapsulation
  • Routing
  • De-encapsulation
• Characteristics of IP

  • Connectionless
  • Best Effort
  • Media Independent
• Network layer receives this from control information sent by the data link layer. Maximum Transmission Unit (MTU).
• Fragmentation is when Layer 3 splits the IPv4 packet into smaller units.
• IPv4 is the primary communication protocol for the network layer.
• The IPv4 network header characteristics:

  • It is in binary
  • Contains several fields of information
  • Diagram is read from left to right, 4 bytes per line
  • The two most important fields are the source and destination.
• IPv4 has three major limitations:

  • IPv4 address depletion
  • Lack of end-to-end connectivity
  • Increased network complexity
• Network Address Translation (NAT) was meant as temporary solution and creates issues on the network as a side effect of manipulating the network headers addressing.
• IPv6 was developed by Internet Engineering Task Force (IETF).
• True or False. IPv6 overcomes the limitations of IPv4. True
• Improvements that IPv6 provides:

  • Increased address space
  • Improved packet handling
  • Eliminates the need for NAT
• The IPv6 header is simplified but not smaller, is fixed at 40 Bytes or octets long.
• Packet are always created at the source. Each host devices creates their own routing table.
• A host can send packets to the following:

  • Itself
  • Local Hosts - destination is on the same LAN
  • Remote Hosts - devices are not on the same LAN
• The Source device determines whether the destination is local or remote.
• A router or layer 3 switch can be a default-gateway.
• Features of a default gateway (DGW):

  • It must have an IP address in the same range as the rest of the LAN.
  • It can accept data from the LAN and is capable of forwarding traffic off the LAN.
  • It can route to other networks.
• IPv6 sends the DGW through a router solicitation (RS) or can be configured manually.
• A Default Gateway (DGW) is static route which will be a last resort route in the routing table.
• route print or netstat -r to display the PC routing table.
• Interface list contains all potential interfaces and MAC addressing.
• There are three types of routes in a router's routing table:

  • Directly Connected - These routes are automatically added by the router, provided the interface is active and has addressing.
  • Remote - These are the routes the router does not have a direct connection and may be learned Manually or Dynamically.
  • Default Route - This forwards all traffic to a specific direction when there is not a match in the routing table.
• The show ip route command shows the following route sources:

  • L - Directly connected local interface IP address
  • C - Directly connected network
  • S - Static route was manually configured by an administrator
  • O - OSPF
  • D - EIGRP
• This command shows types of routes:

  • Directly Connected - C and L
  • Remote Routes - O, D, etc.
  • Default Routes - S
• Local traffic is dumped out the host interface to be handled by an intermediary device.
• Remote traffic is forwarded directly to the default gateway on the LAN.
• The host will know the default gateway (DGW) either statically or through DHCP in IPv4.
• Method of determination:

  IPv4 – Source uses its own IP address and Subnet mask, along with the destination IP address.

  IPv6 – Source uses the network address and prefix advertised by the local router.