On a Debian system using the traditional ifupdown scheme, which stanza in /etc/network/interfaces brings up eth0 at boot with an address obtained from a DHCP server?

LPIC-1 Exam 102-500, objective 109. Networking fundamentals medium

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The options

Not correct auto eth0 iface eth0 inet static

Wrong. The `static` method requires you to supply address, netmask and gateway lines yourself; it never contacts a DHCP server.

Not correct auto eth0 iface eth0 inet loopback

Wrong. The `loopback` method exists for the lo interface only and configures 127.0.0.1.

Not correct allow-hotplug eth0 iface eth0 dhcp

Wrong as written. interfaces(5) defines the stanza as `iface <name> <address_family> <method>`, so the family keyword is required: it has to read `iface eth0 inet dhcp`. (allow-hotplug itself is a valid keyword and means bring the interface up when the kernel reports the device appearing.)

Correct auto eth0 iface eth0 inet dhcp

Correct. `auto eth0` marks the interface to be started by `ifup -a` at boot, and `iface eth0 inet dhcp` selects the IPv4 family with the DHCP method, so a client obtains the address, mask, gateway and DNS servers from the server.

Why

The stanza syntax is `iface IFACE FAMILY METHOD`, where the family is inet (IPv4) or inet6 (IPv6) and common methods are static, dhcp, loopback and manual. `auto` starts the interface during boot; `allow-hotplug` starts it when the device appears. Static stanzas add indented `address`, `netmask` (or CIDR in the address) and `gateway` options. Apply changes with ifup and ifdown. Red Hat family systems instead use /etc/sysconfig/network-scripts/ifcfg-* or NetworkManager keyfiles, so this file is Debian-specific.

Where this comes from

Cited
LPI exam objective 109.2
What it says
Configure a network interface persistently on Debian-style systems.

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