ccna
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Certainly! Here’s a polished and comprehensive version of your CCNA CLI notes, with additional information and examples:
---
## Cisco CLI Modes
1. **User Exec Mode**
- **Prompt:** router>
- **Access:** Limited; used for basic monitoring and troubleshooting commands.
- **Example Command:** show version (Displays information about the router's hardware and software version.)
2. **Privileged Exec Mode**
- **Prompt:** router#
- **Enter with:** enable command from User Exec Mode.
- **Access:** Full access to view configurations, restart the device, and more.
- **Note:** Changes to the configuration must be made in Global Configuration Mode. You can save configurations here.
- **Example Command:** show running-config (Displays the current active configuration.)
3. **Global Configuration Mode**
- **Prompt:** router(config)#
- **Enter with:** configure terminal from Privileged Exec Mode.
- **Access:** Used to make global changes to the configuration of the router or switch.
- **Example Command:** hostname Router1 (Changes the router's hostname to Router1.)
---
## Commands and Operations
- **Help and Auto-Completion**
- **Display Available Commands:** ? (Shows a list of commands available in the current mode.)
- **Auto-Completion:** Use the Tab key to automatically complete commands or parameters.
- **Configuration Commands**
- **Enter Global Configuration Mode:** conf t or configure terminal.
- **Exit Configuration Mode:** exit (Returns to Privileged Exec Mode; repeat to log out.)
- **Password Configuration**
- **Set Enable Password:** enable password <password> (Less secure; passwords are stored in plaintext.)
- **Set Enable Secret:** enable secret <password> (More secure; passwords are stored in MD5 hash.)
- **Password Encryption**
- **Enable Encryption:** service password-encryption (Encrypts plaintext passwords in show running-config.)
- **Disable Encryption:** no service password-encryption (Existing passwords remain encrypted.)
- **Configuration Files**
- **Current Active Configuration:** running-config
- **Configuration Loaded on Restart:** startup-config
- **Saving Configurations**
- **Save Running Config to Startup Config:** write memory or copy running-config startup-config
- **Alias:** write is an alias for write memory.
- **Viewing Configurations**
- **View Current Configuration:** show running-config
- **View Saved Configuration:** show startup-config
- **Command Removal**
- **Remove or Disable a Command:** no <command>
---
## Summary
- **User Exec Mode:** router>
- **Privileged Exec Mode:** router#
- **Enter with:** enable
- **Global Configuration Mode:** router(config)#
- **Enter with:** configure terminal
---
## Examples
- **Set Enable Password:**
- Command: router(config)# enable password mypassword
- **Encrypt Passwords:**
- Command: router(config)# service password-encryption
- **Set Enable Secret:**
- Command: router(config)# enable secret mysecurepassword
- **Save Configuration:**
- Command: router(config)# copy running-config startup-config
---
## Quiz
1. **What cable is used to connect to a Cisco device via RJ45?**
- **Answer:** A rollover cable (one end RJ45, the other end DB9).
2. **If the enable password is not accepted, what could be the problem?**
- **Answer:** Caps Lock might be on.
3. **What is the most secure method to protect access to Privileged Exec Mode?**
- **Answer:** Use enable secret.
4. **If both enable secret and enable password are set, which is used?**
- **Answer:** Only the enable secret is used.
5. **What is the full command for Global Configuration Mode?**
- **Answer:** configure terminal
---
## MAC Address Table Commands
- **View MAC Address Table:**
- **Command:** show mac address-table
- **Description:** Displays the MAC address table.
- **Clear Dynamic MAC Address Table:**
- **Command:** clear mac address-table dynamic
- **Description:** Clears all dynamic MAC addresses.
- **Clear Specific MAC Address:**
- **Command:** clear mac address-table dynamic address <mac-address>
- **Description:** Clears a specific MAC address.
- **Clear MAC Address from a Specific Interface:**
- **Command:** clear mac address-table dynamic interface <interface>
- **Description:** Clears MAC addresses from a specific port/interface.
---
## IP Interface Commands
- **Show IP Interfaces Brief:**
- **Command:** show ip interface brief
- **Description:** Displays a summary of interfaces and their assigned IP addresses.
- **Note:** If the status is admin down, it means the interface has been disabled with the shutdown command.
- **Enter Interface Configuration Mode:**
- **Command:** interface <interface>
- **Description:** Enter configuration mode for a specific interface.
- **Example:** interface g0/0
- **Assign IP Address to Interface:**
- **Command:** ip address <ip-address> <subnet-mask>
- **Description:** Assigns an IP address and subnet mask to the interface.
- **Example:** ip address 192.168.1.1 255.255.255.0
- **Enable Interface:**
- **Command:** no shutdown
- **Description:** Activates the interface.
- **Show Interfaces Brief:**
- **Command:** do show ip interface brief
- **Description:** Displays a summary of interface statuses and IP addresses.
- **Show Detailed Interface Information:**
- **Command:** show interfaces <interface>
- **Description:** Displays detailed information about the specified interface.
- **Show Interface Descriptions:**
- **Command:** show interfaces description
- **Description:** Displays any descriptions added to interfaces.
- **Set Interface Description:**
- **Command:** description <description-text>
- **Example:** description Connected to SW1 port 1
---
This should cover most of the essential details and examples for working with Cisco CLI. Let me know if there’s anything else you’d like to add or modify!
Here’s a polished version of your notes:
---
### Ethernet Frame Header
- Preamble
- Length: 7 bytes / 56 bits
- Purpose: Allows devices to synchronize receiver clocks to ensure they can properly receive the rest of the frame.
- SFD (Start Frame Delimiter)
- Length: 1 byte
- Purpose: Marks the end of the preamble and the beginning of the Ethernet frame.
- Destination Address
- Length: 6 bytes
- Purpose: Specifies the MAC address of the intended recipient.
- Source Address
- Length: 6 bytes
- Purpose: Identifies the MAC address of the sending device.
- Type/Length Field
- Length: 2 bytes
- Purpose: Indicates the type of the encapsulated packet or the length of the data.
- FCS (Frame Check Sequence)
- Length: 4 bytes
- Purpose: Detects corrupted data using a Cyclic Redundancy Check (CRC).
---
### MAC Address
- Length: 6 bytes
- Also Known As: BIA (Burned-In Address)
- Characteristics:
- Globally unique identifier.
- The first 3 bytes represent the OUI (Organizationally Unique Identifier), assigned to the manufacturer.
- The last 3 bytes are unique to the specific device.
- Written as 12 hexadecimal characters.
---
### Unicast Frame
- Definition: A frame destined for a single target device.
### Switch Behavior
- MAC Address Table: Switches store known MAC addresses in this table.
- Unknown Unicast Frame: When a frame’s destination MAC address is unknown, the switch floods the frame out of all interfaces except the one from which it was received.
- Dynamic MAC Address Removal: Dynamic MAC addresses are removed from the MAC address table after 5 minutes of inactivity.
The preamble and sfd are usually not considered part of the ethernet header
Minimum size for an ethernet frame is 64 bytes (header + payload/packet + trainer)
64 bytes - 18 bytes/header and trailer =46 bytes
Minimun payload os 46 bytes
If the payload is less than 46 bytes padding bytes are added.
ARP is used to discover the layer 2 address of a known layer 3 address
Consist of 2 messages
Arp request and arp reply
Arp request is send as broadcast/all host
Arp reply is unicast/1 host
Ffff.ffff.ffff is broadcast address
Know unicast frame/ something in the mac address table = forward not flood
Ping
Test reachability
Measures round trip time
Ping uses 2 messages
Icmp echo request and icmp echo reply
Network lay privides connectivity between hosts on different netwokrs
Provides logical addressing (ip)
Provides path selection between source and destination
Routers op at layer 3
Input IPv4 address classes here
Input basic of IPv4
If host portion is all 0's that is the network address
If host is all 1's that is the broadcast address
This means that if you have an address of 192.168.1.1/24
You have 255 possible addresses but only 253 usable addresses
Half duplex
Can only send OR receive
Full duplex
Can send and receive
CSMA/CD
Before sending frames, devices listen to the collision domain until they detect that it is free to send and other devices arent sending.
If a collision does accur the device send a hamming signal to inform the other deives that a collision has happened
One the other devices have been notified each device will wait a random period of time beofre sending frames again.
Speed/duplex auto negotiantion
Cisco switches and routers are able to be on auto negotiate for the speed and duplex of the interface.
Show mac address-table
Shows amc address table
Clear mac address-table dynamic
Clears the dynamic mac address table
Clear mac address-table dynamic address xxxx.xxxx.xxxx
Used to clear specific addres.
Clear mac address-table dynamic interface Gi0/0
Clears a mac address from a specific port/interface.
Show ip interface brief
Shows the interfacesa and assigned ip addreses
If status is admin down state that means it has been disabled with the shutdown cmd
Admin down is default for cisco routers
Cisco switches are NOT down by default