# Cheatsheet & Examples: ip

The `ip` command is a powerful utility in Linux for managing network interfaces, routing, and address assignments. It replaces older tools like `ifconfig` and `route`.

## Display interface information  
Example Usage:  
`ip a`  
`ip addr show`  

What it does:  
Shows details of all network interfaces, including IP addresses, MAC addresses, and status.  

Command-line Arguments Explained:  
- `a`: Shorthand for `addr` (address information).  
- `show`: Displays the requested information.  
- `dev`: Optional flag to filter by a specific interface (e.g., `ip a show dev eth0`).  

## Show routing table  
Example Usage:  
`ip route show`  
`ip r`  

What it does:  
Displays the kernel’s routing table, including default routes, networks, and gateways.  

Command-line Arguments Explained:  
- `route`: Subcommand to manage routing information.  
- `show`: Displays the routing table.  
- `r`: Shorthand for `route`.  

## Add or remove a route  
Example Usage:  
`ip route add default via 192.168.1.1 dev eth0`  
`ip route del 10.0.0.0/24 via 192.168.1.2`  

What it does:  
Modifies the routing table by adding or deleting a route.  

Command-line Arguments Explained:  
- `add`: Adds a new route.  
- `del`: Deletes an existing route.  
- `default`: Specifies the default gateway.  
- `via`: Defines the gateway IP address for the route.  
- `dev`: Specifies the network interface used for the route.  
- `dst`: The destination network or IP address (e.g., `10.0.0.0/24`).  

## Manage ARP table entries  
Example Usage:  
`ip neigh show`  
`ip neigh add 192.168.1.1 lladdr 00:11:22:33:44:55 dev eth0`  

What it does:  
Displays or adds entries to the ARP (Address Resolution Protocol) table, which maps IP addresses to MAC addresses.  

Command-line Arguments Explained:  
- `neigh`: Subcommand for ARP table management.  
- `show`: Displays the current ARP entries.  
- `add`: Adds a new ARP entry.  
- `lladdr`: The MAC address to associate with the IP.  
- `dev`: The interface where the ARP entry is applied.  

## Bring a network interface up or down  
Example Usage:  
`ip link set eth0 up`  
`ip link set eth0 down`  

What it does:  
Enables or disables a specific network interface (e.g., `eth0`).  

Command-line Arguments Explained:  
- `link`: Subcommand to manage network interfaces.  
- `set`: Modifies the interface’s properties.  
- `up`: Enables the interface.  
- `down`: Disables the interface.  
- `eth0`: The name of the network interface.  

## Add an IP address to an interface  
Example Usage:  
`ip addr add 192.168.1.100/24 dev eth0`  

What it does:  
Assigns a new IP address to a specified network interface.  

Command-line Arguments Explained:  
- `addr`: Subcommand for address management.  
- `add`: Adds a new IP address.  
- `192.168.1.100/24`: The IP address and subnet mask.  
- `dev`: Specifies the network interface (e.g., `eth0`).  

## List all network devices  
Example Usage:  
`ip link show`  
`ip l`  

What it does:  
Displays all network interfaces and their statuses (up/down, MAC address, etc.).  

Command-line Arguments Explained:  
- `link`: Subcommand for interface-level operations.  
- `show`: Displays interface details.  
- `l`: Shorthand for `link`.  

## Check interface statistics  
Example Usage:  
`ip -s a`  
`ip -s link show`  

What it does:  
Displays detailed statistics for network interfaces (e.g., packets sent/received).  

Command-line Arguments Explained:  
- `-s`: Enables detailed statistics (short for `--statistics`).  
- `a`: Shorthand for `addr` (address information).  
- `link`: Subcommand for interface-level operations.  
- `show`: Displays interface details.  

## Show all IPv4 addresses in brief format  
Example Usage:  
`ip -br a`  
`ip -br addr show`  

What it does:  
Lists IPv4 addresses in a compact, easy-to-read format.  

Command-line Arguments Explained:  
- `-br`: Enables brief output mode.  
- `a`: Shorthand for `addr`.  
- `show`: Displays address information.  

## Flush routes from the routing table  
Example Usage:  
`ip route flush all`  
`ip route flush cache`  

What it does:  
Clears all routes or the routing cache, forcing the system to relearn routes.  

Command-line Arguments Explained:  
- `flush`: Deletes all routes or the routing cache.  
- `all`: Removes all routes.  
- `cache`: Clears the routing cache (not the routing table).