Ubuntu DHCP如何迁移服务器

Ubuntu DHCP Server Migration Steps

Migrating a DHCP server on Ubuntu involves backing up configurations and lease data from the old server, installing ISC DHCP on the new server, restoring the data, and validating the new service. Below is a structured guide to ensure a smooth transition:

1. Pre-Migration Preparation

Before starting, ensure you have administrative access to both the old and new Ubuntu servers, and that the new server meets hardware/network requirements (e.g., static IP, correct subnet).
Key prerequisites:

Backup tools (e.g., rsync, scp) installed.
Network connectivity between the old and new servers (for data transfer).
Sufficient storage on the new server for DHCP files.

2. Backup Old DHCP Server Data

The DHCP server’s configuration and lease data must be preserved to avoid reconfiguring from scratch.

Backup Configuration File: The main config file (/etc/dhcp/dhcpd.conf) contains subnet definitions, options (e.g., DNS, gateway), and reservations.
```
sudo cp /etc/dhcp/dhcpd.conf /etc/dhcp/dhcpd.conf.bak
```
Backup Lease Database: The lease file (/var/lib/dhcp/dhcpd.leases) tracks assigned IPs and client information.
```
sudo cp /var/lib/dhcp/dhcpd.leases /var/lib/dhcp/dhcpd.leases.bak
```
Optional: Compress for Transfer: To simplify copying, compress the backup files into a single archive.
```
sudo tar -czvf dhcp_backup.tar.gz /etc/dhcp/dhcpd.conf.bak /var/lib/dhcp/dhcpd.leases.bak
```

3. Install ISC DHCP on the New Server

The new server needs the ISC DHCP package installed to run the DHCP service.

sudo apt update
sudo apt install isc-dhcp-server

During installation, the package will create default config files (e.g., /etc/dhcp/dhcpd.conf). You’ll replace these with the old server’s configs in later steps.

4. Restore Configuration and Lease Data

Transfer the backed-up files from the old server to the new one and place them in the correct directories.

Copy Config File: Use scp (secure copy) or a USB drive to transfer the compressed backup to the new server. Extract it and move the config file to /etc/dhcp/.

scp user@old_server_ip:/path/to/dhcp_backup.tar.gz /tmp/
tar -xzvf /tmp/dhcp_backup.tar.gz -C /tmp/
sudo mv /tmp/etc/dhcp/dhcpd.conf.bak /etc/dhcp/dhcpd.conf

Copy Lease File: Similarly, transfer and place the lease file in /var/lib/dhcp/.
```
sudo mv /tmp/var/lib/dhcp/dhcpd.leases.bak /var/lib/dhcp/dhcpd.leases
```
Adjust Permissions: Ensure the lease file has the correct ownership (typically dhcpd:dhcpd) to allow the DHCP service to read/write it.
```
sudo chown dhcpd:dhcpd /var/lib/dhcp/dhcpd.leases
```

5. Configure the New DHCP Server

Update the new server’s network interface and DHCP settings to match the old server’s configuration.

Edit Interface Configuration: Open /etc/default/isc-dhcp-server and specify the network interface(s) the DHCP service should listen on (replace eth0 with your actual interface, e.g., ens33).
```
sudo nano /etc/default/isc-dhcp-server
```
Modify the INTERFACESv4 line:
```
INTERFACESv4="eth0"
```
Review DHCP Config: Open /etc/dhcp/dhcpd.conf and verify key parameters (subnet, range, options, reservations) match the old server’s setup. Pay special attention to:
- Subnet and netmask (e.g., subnet 192.168.1.0 netmask 255.255.255.0).
- IP range (e.g., range 192.168.1.10 192.168.1.100).
- Router/gateway (e.g., option routers 192.168.1.1).
- DNS servers (e.g., option domain-name-servers 8.8.8.8, 8.8.4.4).
- Reserved IPs (static mappings for devices like printers).
  Example config snippet:
```
authoritative;
subnet 192.168.1.0 netmask 255.255.255.0 {
    range 192.168.1.10 192.168.1.100;
    option routers 192.168.1.1;
    option domain-name-servers 8.8.8.8, 8.8.4.4;
}
```

6. Start and Validate the New DHCP Service

Activate the DHCP service on the new server and confirm it’s running correctly.

Start the Service:
```
sudo systemctl start isc-dhcp-server
```
Check Service Status: Ensure the service is active (no errors).
```
sudo systemctl status isc-dhcp-server
```
Look for “active (running)” in the output.
Test DHCP Functionality: On a client device (or a test VM on the same network), release and renew the IP lease to get an IP from the new server.
```
sudo dhclient -r eth0  # Release current lease
sudo dhclient eth0     # Request new lease
```
Verify the assigned IP is within the new server’s range (use ip a or ifconfig on the client).

7. Decommission the Old DHCP Server

Once the new server is confirmed to be working, disable the DHCP service on the old server to prevent conflicts.

Stop the Old Service:
```
sudo systemctl stop isc-dhcp-server
```
Disable Auto-Start: Prevent the service from starting on boot.
```
sudo systemctl disable isc-dhcp-server
```
Optional: Remove Old Software: If the old server won’t be used for other purposes, uninstall ISC DHCP to free up resources.
```
sudo apt remove --purge isc-dhcp-server
```

Post-Migration Checks

Monitor Logs: Check the new server’s logs for errors or warnings (e.g., journalctl -u isc-dhcp-server or /var/log/syslog).
Verify All Clients: Ensure all devices on the network can obtain IP addresses from the new server.
Update Documentation: Record the new server’s IP, configuration changes, and any modifications made during migration.

By following these steps, you can migrate your Ubuntu DHCP server with minimal downtime and ensure uninterrupted IP address management for your network.