Chapter 6 Network layer

Chapter 6 Network layer

1. network layer of the OSI model specify the addressing and processes that allow the data packets of the network layer to be assembled and transported.

   • Terminal Addressing:
     • must be configured with a unique IP address to identify them on the network.
   • Encapsulation
     • The encapsulation process adds IP header information
   • Routing
     • is to select the best route and direct the packages to the destination host
   • Desencapsulamiento
     • header matches your own IP address, the packet’s IP header is removed and transferred to the appropriate service in the transport layer
   • Network layer protocols
     • Internet Protocol version 4 (IPv4)
     • Internet Protocol version 6 (IPv6)
   • IP encapsulation
     • services are scaled in the different layers without affecting the other layers
     • IP features
       • to send a packet from a source to a destination through an interconnected network system.
     • IP: No connection
       • It means that an exclusive complete connection is not generated before sending the data
     • The IP protocol does not guarantee that all packets that are sent, in fact, are received
     • IP: Independent of the media
       • The OSI data link layer is responsible for preparing IP packets for transmission through the communication medium
   • IPv4 packet header
     • Version
       • It contains a 4-bit binary value set to 0100 that identifies it as an IP packet
     • DiffServ (DS):
       • It is used to determine the priority of each package
     • TTL)
       • It is used to delimit the life of a package
     • Protocol
       • indicates the type of data load that the packet carries, which allows the network layer to transmit the data to the protocol
   • IPv4 limitations
     • Depletion of IP addresses
       • a limited number of unique public IPv4 addresses available
     • Internet routing table expansion:
       • to determine the best routes. As the number of servers connected to the Internet increases, the number of network routes also increases
     • Lack of complete connectivity
       • provides a way for multiple devices to share a single public IPv4 address.
     • Introduction to IPv6
       • Greater address space
       • Better package handling
       • The need for NAT is eliminated
       • IPv6 encapsulation
       • IPv6 encapsulation
         • Version
           • Contains a 4-bit binary value set to 0110
         • Traffic class
           • This 8-bit field is the equivalent to the IPv4 DS field
         • Flow label
           • suggests that all packets with the same flow tag receive the same type of routers handling.
         • Content Length
           • indicates the length of the data portion or the content length of the IPv6 packet
         • Next Header
           • It is a value that indicates the type of data content that the packet carries, which allows the network layer to transmit the information
         • Jump Limit
           • Each router that forwards the packet reduces this value by 1. When it reaches zero, the packet is discarded
         • Source IPv6 Address
           • It is a 128-bit field that identifies the IPv6 address of the sending host.
         • Destination IPv6 Address
           • It is a 128-bit field that identifies the IPv6 address of the receiving host.

2. The host forwarding decision

   • Likewise
     • A host can ping itself by sending a packet to an address
   • To the local host:
     • This is a host that is on the same local network as the sending host. The hosts share the same network address
   • To a remote I / O module
     • This is a host on a remote network. The hosts do not share the same network address.
   • Default gateway
     • it is the network device that can route traffic to other networks
   • Host routing tables
     • Interfaces list
       • a list of media access control (MAC) addresses and interface number
     • IPv4 route table
       • list of all known IPv4 routes, including direct connections, local networks and default local routes
     • IPv6 route table
       • list of all known IPv6 routes, including direct connections, local networks and default local routes
   • router packet delivery
     • Routes directly connected
       • come from active router interfaces is connected to a different network segment
     • Remote routes
       • routes come from remote networks connected to other routers routes are configured to these networks manually on the local router
     • Default route
       • Like a host, routers also use the default routes
   • local route entry
     • C: Identify a directly connected network
     • L: Indicates that this is a local interface

3. router

   • branch office
     • Small businesses and medium-sized branch sites
   • WAN
     • Large companies, organizations and companies
   • Service provider
     • Large service providers
   • (CPU).
     • to execute the OS instructions
   • SO
     • provide routing and switching functions.
   • Memoria del router
     • RAM:
       • store applications, processes and the necessary data
     • ROM
       • to store crucial operating instructions and a limited IOS
     • NVRAM
       • use as permanent storage for the startup configuration file
     • Flash
       • as permanent storage of IOS and other system related files
     • WAN and LAN interfaces
       • Console
         • physical management that provides out-of-band access to a device
       • Shell seguro (SSH)
         • remotely establish a secure CLI connection through a virtual interface
       • Telnet
         • insecure method to establish a CLI session remotely through a virtual interface through a network

4. router configuration

   • Default gateway
     • used only when the host wishes to send a packet to a device on another network
     • the router interface address connected to the host's local network
   • Default gateway for a switch
     • It is configured on all devices that wish to communicate beyond the local network