LPIC-2 Advanced Networking Configuration Practice Question
An administrator needs to create a Linux bridge (br0) and add an Ethernet interface (eth1) to it for KVM virtual machine networking. Which set of commands accomplishes this task?
⚠ Common exam trap
Many candidates confuse the purpose of `bridge fdb` (which manages the forwarding database) with the command to add an interface to a bridge, or they assume that `ip link set ... master` alone is sufficient without bringing the bridge up.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
brctl addbr br0; brctl addif br0 eth1
`brctl addbr br0` creates a new bridge interface named br0, and `brctl addif br0 eth1` adds the physical Ethernet interface eth1 as a port of that bridge. This is the standard sequence using the legacy bridge utilities to set up a bridge for KVM virtual machine networking, where eth1 becomes a member of br0, allowing VMs to share the physical network.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
ifconfig br0 up; ifconfig eth1 up; brctl addbr br0; brctl addif br0 eth1
Why it's wrong here
Order is incorrect; bridge must exist before adding interfaces.
- ✗
ip link add br0 type bridge; ip link set eth1 master br0
Why it's wrong here
While 'iproute2' can manage bridges, this syntax is incomplete and not the traditional method tested on LPIC-2.
- ✓
brctl addbr br0; brctl addif br0 eth1
Why this is correct
Standard bridge-utils commands to create bridge and add interface.
- ✗
brctl addbr br0; bridge fdb add dev eth1 master br0
Why it's wrong here
The 'bridge fdb' command manages MAC addresses, not interface membership.
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