Virtual network interfaces (like eth0:1) are commonly used for hosting multiple IP addresses on a single physical interface. However, DHCP clients typically don't work as expected with these virtual interfaces due to how they interact with the kernel's networking stack.

The fundamental issue lies in how DHCP operates:

# This works because the primary interface exists in the kernel's ARP table
dhclient eth0
ifconfig eth0:1 192.168.1.105 up

# This fails because virtual interfaces don't initiate ARP properly
ifconfig eth0 192.168.1.105 up
dhclient eth0:1

Here are several approaches to achieve DHCP on virtual interfaces:

Method 1: DHCP on Primary Interface, Then Add Virtual

# First get DHCP on main interface
dhclient eth0

# Then add virtual interface with static IP
ifconfig eth0:1 192.168.1.105 up

Method 2: Using macvlan for True Virtual Interfaces

# Create macvlan device
ip link add link eth0 name eth0v1 type macvlan

# Bring it up
ip link set eth0v1 up

# Now you can use dhclient
dhclient eth0v1

Method 3: Network Manager Configuration

For systems using NetworkManager:

nmcli con add type ethernet ifname eth0 ipv4.method auto
nmcli con add type ethernet ifname eth0:1 ipv4.method manual ipv4.addresses 192.168.1.105/24

For more control, edit /etc/dhcp/dhclient.conf:

interface "eth0:1" {
    send host-name "myvirtualhost";
    request subnet-mask, broadcast-address, routers, domain-name-servers;
    require subnet-mask, domain-name-servers;
}

Consider these specialized DHCP clients for complex scenarios:

• dhcpcd - Handles virtual interfaces better in some cases
• pump - Older but simpler DHCP client
• udhcpc - Busybox's lightweight client

When debugging virtual interface DHCP issues:

# Check interface status
ip addr show eth0:1

# Monitor DHCP traffic
tcpdump -i eth0 port 67 or port 68

# Verify dhclient logs
journalctl -u dhclient

---

When working with virtual network interfaces in Linux (like eth0:1), many developers encounter unexpected behavior with DHCP configuration. The standard approach works perfectly for primary interfaces:

dhclient eth0
ifconfig eth0:1 192.168.1.105 up

But the reverse configuration fails:

ifconfig eth0 192.168.1.105 up
dhclient eth0:1

Virtual interfaces (aliases) are fundamentally different from physical interfaces in how they handle DHCP:

• DHCP clients typically bind to physical interfaces only
• Virtual interfaces lack their own MAC addresses
• The kernel networking stack treats them as secondary entities

Method 1: Using dhclient with Interface Specification

The most reliable approach uses dhclient's advanced options:

dhclient -v -i -pf /var/run/dhclient.eth0:1.pid \
-lf /var/lib/dhcp/dhclient.eth0:1.leases eth0:1

Key flags:

• -i: Allow non-standard interface names
• -pf: Specify PID file location
• -lf: Custom lease file location

Method 2: Network Manager Configuration

For systems using NetworkManager, create a connection profile:

nmcli con add type ethernet ifname eth0:1 \
ipv4.method auto con-name "eth0-virtual-dhcp"

For more robust virtual interface management, consider VLAN tagging:

vconfig add eth0 10
dhclient eth0.10

If you still encounter issues:

# Check DHCP discovery packets
tcpdump -i eth0:1 -n port 67 or port 68

# Verify interface status
ip addr show eth0:1

# Examine DHCP client logs
journalctl -u dhclient --no-pager

Remember that virtual interfaces aren't designed for DHCP out of the box, but these techniques provide workable solutions for development environments and specific use cases.