# 🌐 Phase 2: Networking

> Goal: Machines communicate — ping, SSH, file transfers, services

---

## 🎯 Exercise 1 — Ping & IPs

```bash
# Check your network
ip addr show eth0
ip route

# Ping the other lab VM
ping -c 4 10.0.1.2        # From alpine-1 → alpine-2
ping -c 4 10.0.1.1        # From alpine-2 → alpine-1

# Check ARP table
ip neigh

# tcpdump (packet capture) — Alpine needs install first
apk add tcpdump
tcpdump -i eth0 -c 5 icmp &
ping -c 3 10.0.1.2
```

### 📝 Questions:
1. What's the MAC address of the other VM?
2. Can you ping alpine-hop (10.0.1.3) from alpine-1?
3. What subnet are you on? How many usable hosts?

---

## 🎯 Exercise 2 — SSH Keys

```bash
# Step 1 — Generate an SSH key pair
ssh-keygen -t ed25519
# Press Enter for all prompts (no passphrase)

# Step 2 — What just got created?
ls -la ~/.ssh/
# id_ed25519      ← your PRIVATE key (NEVER share this!)
# id_ed25519.pub  ← your PUBLIC key (safe to share)

# Step 3 — Copy your public key to alpine-2
ssh-copy-id root@10.0.1.2
# Enter root password for alpine-2 when prompted

# Step 4 — Test passwordless login!
ssh root@10.0.1.2 'hostname; uptime'
# Should work WITHOUT asking for a password 🎉

# Step 5 — See what ssh-copy-id did
ssh root@10.0.1.2 'cat ~/.ssh/authorized_keys'
```

### 💡 How it works
Your public key is appended to `~/.ssh/authorized_keys` on the target. When you SSH, the server checks if you have the matching **private key** — no password needed! 🔑

---

## 🎯 Exercise 3 — File Transfer (SCP & RSYNC)

```bash
# SCP — single files
echo "CCNA study notes" > /root/study.txt
scp /root/study.txt root@10.0.1.2:/root/

# Verify
ssh root@10.0.1.2 'cat /root/study.txt'

# RSYNC — directories (need to install on Alpine)
apk add rsync
rsync -av /root/lab/ root@10.0.1.2:/root/lab-backup/

# Verify the backup
ssh root@10.0.1.2 'ls -la /root/lab-backup/'
```

### 📝 Questions:
1. What's the difference between `scp` and `rsync`?
2. What does the `-a` flag in `rsync -av` mean? (hint: check `man rsync`)

---

## 🎯 Exercise 4 — Network Services

```bash
# Check what's listening on your VM
ss -tlnp

# Start a simple HTTP server on alpine-1
python3 -m http.server 8080 &

# Access it from alpine-2
curl http://10.0.1.1:8080/

# See the connection in your server logs
# Kill the server when done
kill %1
```

---

## 🎯 Bonus: CCNA Challenge

```bash
# From alpine-1, can you SSH to alpine-hop?
ssh root@10.0.1.3

# Check the routing table
ip route

# Why can alpine-1 reach alpine-hop (10.0.1.3)?
# Why can't alpine-1 reach the internet?
```

---

## ✅ Phase 2 Checklist

- [ ] Ping and ARP (`ip neigh`)
- [ ] SSH key generation and passwordless login
- [ ] File transfer with `scp` / `rsync`
- [ ] Running a network service

**Previous:** [[Phase 1 - Walking]] | **Next:** [[Phase 3 - Users and Files]]