Describe basic routing concepts

chapter 4: IP Routing technologies

    Describe basic routing concepts

  • Routing is a path to finding from one end to the other and routing occurs at layer 3 and bridging occurs at layer 2. Routing Process to forward packets to destination networks.

    Routers don’t really care about hosts they care only about networks and the best path to each network. The logical network address of the destination host is used to get packets to a network through a routed network, and then the hardware address of the host is used to deliver the packet from a router to the correct destination host.

    Routing table is used to find best path to destination. Forwarding decisions based on Layer 3. IP performs search for a matching host address, search for a matching network address, and search for a default entry, Routing done by IP router, when it searches the routing table and decides which interface to end a packet out.

    When a router receives a packet, it examines the destination IP address. If the destination IP address does not belong to any of the router’s directly connected networks, the router must forward this packet to another router.

     
  • Describe basic routing concepts

  • Introduction to IP Routing

    IP routing—the process of forwarding IP packets—delivers packets across entire TCP/IP networks, from the device that originally builds the IP packet to the device that is supposed to receive the packet. In other words, IP routing delivers IP packets from the sending host to the destination host.

    Routers don’t really care about hosts they care only about networks and the best path to each network. The logical network address of the destination host is used to get packets to a network through a routed network, and then the hardware address of the host is used to deliver the packet from a router to the correct destination host.

    Routing table is used to find best path to destination. Forwarding decisions based on Layer 3. IP performs search for a matching host address, search for a matching network address, and search for a default entry, Routing done by IP router, when it searches the routing table and decides which interface to end a packet out.

    When a router receives a packet, it examines the destination IP address. If the destination IP address does not belong to any of the router’s directly connected networks, the router must forward this packet to another router.

    Fig shows Basic IP Routing.
     
    There are two types of Routing:
    1. Static Routing.
    2. Dynamic Routing.
     

    Static Routing:

    Static Routing is typically used in hosts Enter subnet mask, router (gateway), IP address Perfect for cases with few connections, doesn’t change much. Specifies network address and subnet mask of remote network, and IP address of next hop router or exit interface.
     
    Static Routing is Easy to configure and Easier for administrator to understand.
    A static route includes the network address and subnet mask of the remote network, along with the IP address of the next-hop router or exit interface. Static routes should be used in a large network is configured in a hub-and-spoke topology, a network is connected to the Internet only through a single ISP, a network consists of only a few routers.
     
    The static routing method requires someone to hand-type all network locations into the routing table. The network administrator manually enters the routing information in the router. The static routing is used to test a particular link in a network. 
     
    Drawback for Static Routing is a network consists of only a few routers and requires complete knowledge of the whole network for proper implementation and does not scale well with growing networks.
     
     Static Routing

    Dynamic Routing:

    Most routers use dynamic routing automatically builds the routing tables, there are two major approaches Link State Algorithms and Distance Vector Algorithms. Dynamic Routing is used by routers to share information about the reachability and status of remote network. In dynamic routing, a routing protocol on one router communicates with the same routing protocol running on neighbor routers. The routers then update each other about all the networks they know about and place this information into the routing table.
     
    Dynamic Routing has less administrative overhead when adding or deleting a network Protocols automatically react to the topology changes and it is more scalable. Dynamic routing protocols are used by routers to share information about the reachability and status of remote networks.
     
    The dynamic routing is using routing protocol to update routing information. The dynamic routing used as a protocol on one router communicates with the same protocol running on neighboring routers. 
     
    Drawback for Dynamic Routing is more administrator knowledge is required for configuration, verification and troubleshooting and Router resources are used (CPU cycles, memory and link bandwidth).
     
    Dynamic Routing
     

    IP Routing process:

    Step 1:

    •Computer A will analyze (AND)the data packet against its subnet masks
    –The data is to be sent to another subnet  
    •Broadcast for the hardware address (eg: CC) of the gateway (IP address is already known)
    –Using ARP
    •On receiving the hardware address, send the data packet to the gateway (router) to be forwarded to its destination subnet
     

    Step 2:

    •The router will now be able to deliver the data packet to its destination in the other subnet
    •An analysis of the data packet (AND) will determine the destination subnet
    •The gateway will broadcast for the hardware address of the receiving host (IP already known)
    •On receiving a response, the packet will be forwarded to the destination host
     

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