Ccna

If you have forgotten the router’s enable secret password or someone has just given you a second-hand router, and you don’t know it, you need to decrypt it to configure it.

The first thing we need to do is to make sure that the IOS (operating system) is not loaded when the router is turned on, so press the CTRL + BREAK  keys for 60 seconds during boot. With this process, our device is opened with the operating system where mini IOS operations can be performed. ROMMON mode. (ROMMON mode is like a small operating system.)

In this article, I will be talking about the concept of IP and Subnetting.

Now let’s take a little technical approach;

Each system on the network that communicates must have an IP address. IP addressing is used according to the routing layer (layer 3) of the TCP / IP protocol cluster.

IPv4 – IP (Internet Protocol) Addresses

IP addresses (in IPv4) are 32-bit numbers. These numbers are divided into four 8-bit segments for ease of writing and display, as well as the ease of network management. I’m going to call each of these parts Octet later in my article.

What is Network Address Translation?

The Network Address Translation (NAT) functionality in the Cisco routers allows privately addressed networks to connect to public networks such as the Internet. When the privately addressed network (the “inside”) sends a packet through the NAT router, the addresses are converted to legal (registered) IP addresses before being passed to the “outside”.

Many sites have been using pass-through firewall gateways to provide this functionality. Well, it’s now available in your Cisco router!

First of all, I want to quickly answer the question of what is DHCP. DHCP is a service called Dynamic Host Configuration Protocol that allows devices on the network to automatically obtain information such as IP, Default Gateway and DNS. Normally, we now use DHCP with IPv4, but IPv6 introduces two different DHCP services, Stateful and Stateless.

In Stateful DHCP, just like the DHCP server in IPv4, all the necessary information is provided by the DHCP server, and user information (IP and lease, etc.) is stored on the server. In Stateless DHCP, only DNS, etc. information is received from the DHCP server, IP and GW information are automatically generated by the user computer and user information (IP and lease, etc.) is not stored on the server. A computer on an IPv6 network automatically adjusts IP and GW information by utilizing NDP (Neighbor Discovery Protocol) packets from the router on the respective network.

BGP Finite State Machine: Troubleshooting

(See page 108 of the Halabi book for a diagram).

1. Idle

Waiting for Start event, normally initiated by the operator (establishing new BGP session or resetting an existing session). After errors, BGP falls back to the Idle state.

After a Start event, BGP initializes, resets connect retry timer, initiates TCP transport connection, and listens for connections initiated by a remote peer.

2. Connect

BGP is waiting for a transition protocol connection to complete. If TCP transport succeeds, transition to State 4, OpenSent, and send OPEN. If not, transition to Active. If the connect retry timer expires, remain in Connect, reset the timer, and initiate a transport connection. In case of any other event, transition back to Idle.