CCNA Expl 2. Chapter 2. Static routing

CCNA Exploration. 

Routing protocols and Consepts. 

Chapter 2. Resume. Static routing 

        Routers are primarily responsible for interconnecting networks by:

1) Determining the best path to send packets 

2) Forwarding packets toward their destination.

The routers primary forwarding decision is based on Layer 3 information, the destination IP address. 

Straight-through cables are used for:          Crossover cables are used for:
         Switch-to-router                                              Switch-to-switch
         Switch-to-router                                              PC-to-PC
         Switch-to-router                                              Switch-to-hub
         Switch-to-router                                              Hub-to-hub
         Switch-to-router                                              Router-to-router
         Switch-to-PC                                                  Router-to-server
         Hub-to-PC
         Hub-to-server

Static routes and dynamic routes will not be added to the routing table until the appropriate local interfaces, also known as the exit interfaces, have been configured on the router.

The show ip interface brief command can be used to see a portion of the interface information in a condensed format.

The show running-config command displays the current configuration file that the router is using.

The show interfaces command displays the MAC address for the Ethernet interfaces.

The clock rate command will set the clock signal for the link. 

      By default, all router interfaces are shutdown, or turned off. To enable this interface, use the no shutdown command, which changes the interface from administratively down to up.

     The show interfaces fastethernet 0/0 command in the figure now shows that the interface is up, and the line protocol is up. The no shutdown command changed the interface from administratively down to up.

     Serial interfaces require a clock signal to control the timing of the communications. 

     show ip route -we will see the directly connected route.

     debug commands can be used to monitor router operations in real time. 

Cisco Discovery Protocol (CDP) is a powerful network monitoring and troubleshooting tool. CDP is an information-gathering tool used by network administrators to get information about directly connected Cisco devices.

CDP operates at Layer 2 only. 

 Commands: show cdp neighbors and show cdp neighbors detail .

CDP provides the following information about each CDP neighbor device:

1. Device identifiers - For example, the configured host name of a switch
2. Address list - Up to one Network layer address for each protocol supported
3. Port identifier - The name of the local and remote port-in the form of an ASCII character string such as ethernet0
4. Capabilities list - For example, whether this device is a router or a switch
5. Platform - The hardware platform of the device; for example, a Cisco 7200 series router

    A stub network is a network accessed by a single route. 

   The complete syntax for configuring a static route is:

  Router(config)#ip route prefix mask 

The following parameters are used:

• network-address - Destination network address of the remote network to be added to the routing table
• subnet-mask - Subnet mask of the remote network to be added to the routing table. The subnet mask can be modified to summarize a group of networks. 

One or both of the following parameters must also be used:

• ip-address - Commonly referred to as the next-hop router's IP address 
• exit-interface - Outgoing interface that would be used in forwarding packets to the destination network

Routing Table Principles

Principle 1: "Every router makes its decision alone, based on the information it has in its own routing table."

Principle 2: "The fact that one router has certain information in its routing table does not mean that other routers have the same information."

Principle 3: "Routing information about a path from one network to another does not provide routing information about the reverse, or return path."

       Recursive Route Lookup

Before any packet is forwarded by a router, the routing table process must determine the exit interface to use to forward the packet. This is known as route resolvability.

         When the router has to perform multiple lookups in the routing table before forwarding a packet, it is performing a process known as a recursive lookup.

        There are times when a previously configured static route needs to be modified:

• The destination network no longer exists, and therefore the static route should be deleted.
• There is a change in the topology, and either the intermediate address or the exit interface has to be changed.

 Route Summarization

Multiple static routes can be summarized into a single static route if:

                                The destination networks can be summarized into a single network address, and 

                                The multiple static routes all use the same exit-interface or next-hop IP address.