add linux lxc networking

tech_docs/linux/linux_lxc_networking.md

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+Got it, Jason. Let's take a more foundational approach to understanding Linux networking concepts, focusing on bridging your Cisco networking knowledge with Linux networking principles. 
+
+### Basic Concepts of Linux Networking
+
+#### 1. **Network Interfaces**
+Linux systems have multiple network interfaces, similar to physical and virtual interfaces on Cisco devices. These interfaces can be physical (e.g., `eth0`, `wlan0`) or virtual (e.g., `lo` for loopback, `veth` for virtual Ethernet).
+
+- **Physical Interface**: Represents a physical network card (NIC).
+- **Virtual Interface**: Used for virtual networking (e.g., `br0` for a bridge, `tun0` for a tunnel).
+
+#### 2. **IP Addressing**
+IP addresses are assigned to interfaces, just like in Cisco devices. You can use the `ip` command (or older `ifconfig` command) to view and configure IP addresses.
+
+```bash
+# View IP addresses
+ip addr show
+
+# Assign IP address
+sudo ip addr add 192.168.1.10/24 dev eth0
+
+# Bring up the interface
+sudo ip link set dev eth0 up
+```
+
+#### 3. **Routing**
+Routing in Linux can be managed using the `ip` command. The routing table determines where packets are forwarded.
+
+```bash
+# View routing table
+ip route show
+
+# Add a static route
+sudo ip route add 10.0.0.0/24 via 192.168.1.1 dev eth0
+```
+
+#### 4. **Firewall and NAT**
+Linux uses `iptables` (or `nftables` in newer systems) for firewall rules and Network Address Translation (NAT). This is akin to ACLs and NAT rules on Cisco devices.
+
+```bash
+# View current firewall rules
+sudo iptables -L
+
+# Add a simple firewall rule
+sudo iptables -A INPUT -p tcp --dport 22 -j ACCEPT
+
+# Save iptables rules
+sudo iptables-save > /etc/iptables/rules.v4
+```
+
+### Bridging and Virtual Networks
+
+For LXC (Linux Containers) or any containerization, you often deal with bridging, similar to VLANs and sub-interfaces on Cisco devices.
+
+#### 1. **Creating a Network Bridge**
+A bridge allows you to connect multiple network segments at the data link layer.
+
+```bash
+# Create a new bridge
+sudo ip link add name br0 type bridge
+
+# Add an interface to the bridge
+sudo ip link set eth0 master br0
+
+# Bring up the bridge
+sudo ip link set dev br0 up
+```
+
+#### 2. **Using Bridge for Containers**
+You can attach containers to this bridge, so they communicate as if they are on the same network segment.
+
+```bash
+# Assign the bridge to a container (example using LXC config file)
+lxc.network.type = veth
+lxc.network.link = br0
+lxc.network.flags = up
+```
+
+### Port Forwarding and NAT
+
+Port forwarding is used to forward traffic from one IP:port to another, similar to NAT on Cisco devices.
+
+#### 1. **Basic Port Forwarding with `iptables`**
+
+```bash
+# Forward traffic from 192.168.1.10:81 to 10.0.0.1:80
+sudo iptables -t nat -A PREROUTING -d 192.168.1.10 -p tcp --dport 81 -j DNAT --to-destination 10.0.0.1:80
+
+# Allow forwarding
+sudo iptables -A FORWARD -p tcp -d 10.0.0.1 --dport 80 -m state --state NEW,ESTABLISHED,RELATED -j ACCEPT
+
+# Masquerade outgoing packets
+sudo iptables -t nat -A POSTROUTING -j MASQUERADE
+```
+
+### Example Setup: Port Forwarding for LXC Containers
+
+Let's put this all together with an example where you forward ports to LXC containers running Apache.
+
+1. **Set Up the Bridge**:
+
+```bash
+# Create a bridge
+sudo ip link add name br0 type bridge
+sudo ip addr add 192.168.1.1/24 dev br0
+sudo ip link set br0 up
+```
+
+2. **Configure LXC Containers**:
+   - Ensure LXC containers are connected to `br0`.
+   - Assign IP addresses within the `192.168.1.0/24` range to the containers.
+
+3. **Port Forwarding Rules**:
+
+```bash
+# Forward traffic to container 1 (192.168.1.10:80)
+sudo iptables -t nat -A PREROUTING -d 192.168.1.1 -p tcp --dport 81 -j DNAT --to-destination 192.168.1.10:80
+
+# Forward traffic to container 2 (192.168.1.11:80)
+sudo iptables -t nat -A PREROUTING -d 192.168.1.1 -p tcp --dport 82 -j DNAT --to-destination 192.168.1.11:80
+
+# Allow forwarding
+sudo iptables -A FORWARD -p tcp -d 192.168.1.10 --dport 80 -m state --state NEW,ESTABLISHED,RELATED -j ACCEPT
+sudo iptables -A FORWARD -p tcp -d 192.168.1.11 --dport 80 -m state --state NEW,ESTABLISHED,RELATED -j ACCEPT
+
+# Masquerade outgoing packets
+sudo iptables -t nat -A POSTROUTING -j MASQUERADE
+```
+
+### Summary
+
+By understanding these core Linux networking concepts and commands, you can leverage your Cisco networking knowledge to effectively manage and configure Linux-based networks. This foundation will help you handle more advanced scenarios, like managing LXC containers and implementing complex port forwarding and NAT setups.