LPIC-2 Advanced Networking Configuration Practice Test 2 — 15 Questions

Question 1

Which TWO conditions must be met for a Linux bridge to forward traffic between its ports?

Accepted Answer

The bridge has at least two ports added.. A Linux bridge requires at least two ports to forward traffic; a bridge with only one port cannot forward frames between interfaces. Option C is correct because the bridge kernel module must be loaded (e.g., via `modprobe bridge`) to provide the bridging functionality; without it, bridge operations are impossible.

Answer

The bridge has an IP address.

Answer

The interfaces are in promiscuous mode.

Answer

Spanning Tree Protocol is disabled.

Question 2

The server is unable to communicate with hosts on the 192.168.2.0/24 network. Based on the exhibit, what is the most likely cause?

Accepted Answer

The interface has no default gateway configured.. The exhibit shows the interface has an IP address of 192.168.1.10/24 and a default gateway of 0.0.0.0, meaning no default gateway is configured. Without a default gateway, the host cannot route packets to the 192.168.2.0/24 network because that network is not directly connected (it is on a different subnet), and the host has no route to forward traffic beyond its local link. The `route -n` output would confirm the absence of a gateway entry, which is the most likely cause of the communication failure.

Answer

The interface has a duplicate IP address.

Answer

The hardware address is corrupted.

Answer

The subnet mask is incorrect.

Question 3

Hosts connected to eth1 cannot communicate with hosts on eth0. Based on the exhibit, what is the most likely reason?

Accepted Answer

Spanning Tree Protocol has placed eth1 in blocking state.. The exhibit shows a Linux bridge (br0) with eth0 and eth1 as bridge ports. If hosts on eth1 cannot communicate with hosts on eth0, the most likely cause is that Spanning Tree Protocol (STP) has placed eth1 in a blocking state to prevent a Layer 2 loop. STP blocks redundant paths by transitioning ports through listening, learning, and blocking states, and a blocked port does not forward traffic until the topology converges.

Answer

Physical layer issues on eth1.

Answer

Eth1 is not connected to the bridge.

Answer

The bridge interface has no IP address.

Question 4

Traffic from the 10.1.1.0/24 subnet is seen leaving through eth1 as intended, but reply traffic from the internet never comes back. What is the most likely cause?

Accepted Answer

The kernel parameter net.ipv4.conf.all.rp_filter is set to 1.. When `net.ipv4.conf.all.rp_filter` is set to 1, the kernel performs strict reverse path filtering. This means the kernel checks whether the source address of incoming packets can be reached via the interface they arrived on. If reply traffic from the internet arrives on an interface (e.g., eth0) that does not have a route back to the original source subnet (10.1.1.0/24) through that same interface, the kernel drops the packet. This is the most likely cause because the outbound traffic leaves via eth1, but the reply comes back on a different interface, triggering the rp_filter check and causing the reply to be silently discarded.

Answer

The ip rule priority is not set, causing it to be overridden.

Answer

The default route in table 200 points to 172.16.0.1 which does not have a route back to 10.1.1.0/24.

Answer

The router does not have a route back to 10.1.1.0/24 via eth0.

Question 5

A system administrator wants to combine two 1 Gbps Ethernet interfaces into a single logical bonded interface to increase throughput and provide redundancy. Which mode of bonding will provide both load balancing and fault tolerance without requiring switch configuration?

Accepted Answer

mode 6 (balance-alb). Mode 6 (balance-alb) provides adaptive load balancing (ALB) that distributes outgoing traffic based on the MAC address of the destination, and it also handles incoming traffic by ARP negotiation, allowing both load balancing and fault tolerance without any special switch configuration. Unlike other modes that require switch support (e.g., IEEE 802.3ad LACP for mode 4) or specific hashing policies, balance-alb works entirely at the host level, making it the only correct choice for this scenario.

Answer

mode 2 (balance-xor)

Answer

mode 1 (active-backup)

Answer

mode 0 (balance-rr)

Question 6

A company has multiple internet connections and wants to route traffic from specific subnets to specific providers. They are using policy-based routing with ip rule and ip route. After adding the rules, the administrator finds that the traffic is not matching the intended routing table. Which command should be used to verify that the rules are being matched correctly?

Accepted Answer

ip route get mark . 'ip route get' with the 'mark' option simulates a packet lookup using the specified routing mark, allowing the administrator to see which routing table would be matched by the policy rules. This directly verifies whether the ip rule conditions (e.g., fwmark, source subnet) are correctly directing traffic to the intended table.

Answer

ip route show cache

Answer

ip rule show

Answer

ip route show table all

Question 7

To create a simple bridge interface that connects two Ethernet interfaces, which of the following commands should be used?

Accepted Answer

ip link add br0 type bridge && ip link set br0 up. The `ip link add br0 type bridge` command creates a new bridge interface using the modern iproute2 suite, and `ip link set br0 up` activates it. This is the current standard method for bridge creation on Linux, replacing the older brctl tool. The bridge then connects Ethernet interfaces by enslaving them with `ip link set eth0 master br0`.

Answer

brctl addbr br0 && brctl addif br0 eth0 eth1

Answer

ifconfig br0 create && ifconfig br0 up

Answer

Both A and B work correctly

Question 8

An administrator configures a DHCP relay agent using 'dhcrelay' in a network with multiple VLANs. The relay agent is on a Linux server with interfaces eth0 (VLAN 10) and eth1 (VLAN 20). The DHCP server is on VLAN 10. Which command correctly sets up the relay to forward requests from VLAN 20 to the DHCP server at 192.168.1.5?

Accepted Answer

dhcrelay -i eth1 192.168.1.5. The `-i eth1` flag specifies the interface on which the relay agent should listen for DHCP client broadcasts (VLAN 20). The relay then unicasts those requests to the DHCP server at 192.168.1.5, which resides on VLAN 10. This ensures that only broadcasts from the client-side VLAN are forwarded, not those from the server-side network.

Answer

dhcrelay -i eth0 192.168.1.5

Answer

dhcrelay -i eth0 -i eth1 192.168.1.5

Answer

dhcrelay 192.168.1.5

Question 9

An administrator is troubleshooting IPv6 connectivity on a Linux host. The host has an IPv6 address configured on eth0, but cannot ping6 the default gateway. The output of 'ip -6 route show' shows a default route via fe80::1 dev eth0. Which tool should be used to verify that the neighbor discovery process is working?

Accepted Answer

ip neigh show. The 'ip neigh show' command displays the neighbor cache (equivalent to ARP table for IPv6), which is populated by the Neighbor Discovery Protocol (NDP). Since the default gateway is a link-local address (fe80::1), the host must have resolved the gateway's MAC address via NDP before it can send packets. If the neighbor entry is missing or incomplete (e.g., STALE or FAILED), it indicates that the neighbor discovery process is not working, which would explain the ping failure.

Answer

tcpdump -i eth0 icmp6

Answer

traceroute6

Answer

ndp -n

Question 10

A security analyst wants to capture only TCP packets with the SYN flag set to identify connection attempts. Which tcpdump filter expression accomplishes this?

Accepted Answer

Both B and C are correct.. Both B and C correctly filter TCP packets with the SYN flag set. Note that in the question stem, options B and C are incorrectly marked as '[wrong]', but they are actually valid filters. In tcpdump, the TCP header's 14th byte (offset 13) contains the flags, with the SYN flag represented by bit 1 (value 2). Both `tcp[13] & 2 != 0` and `tcp[13] & 0x02 != 0` check if the SYN bit is set, making them equivalent. Option A is syntactically incorrect because `tcp-syn` is not a valid tcpdump primitive; the correct form uses the numeric offset and bitmask.

Answer

tcp[tcpflags] & tcp-syn != 0

Answer

tcp[13] & 2 != 0

Answer

tcp[13] & 0x02 != 0

Question 11

An administrator is configuring netfilter rules to implement a stateful firewall. Which TWO of the following commands are necessary to allow the firewall to correctly forward TCP traffic from internal to external networks (assuming proper default policies)?

Accepted Answer

iptables -A FORWARD -m state --state ESTABLISHED -j ACCEPT. A stateful firewall must allow packets belonging to already established connections to pass through the FORWARD chain. The `-m state --state ESTABLISHED` match ensures that any packet that is part of an existing TCP connection (i.e., has seen the three-way handshake) is accepted, which is essential for forwarding return traffic from external networks back to internal hosts.

Answer

iptables -A FORWARD -m state --state NEW -j ACCEPT

Answer

iptables -A FORWARD -j ACCEPT

Answer

iptables -A FORWARD -m state --state NEW -p tcp --dport 80 -j ACCEPT

Question 12

A packet destined to 192.168.1.100 is sent from this router. Which interface will be used to forward it?

Accepted Answer

The packet will be dropped. Without a routing table or interface IP configuration provided, we cannot assume any interface is on the 192.168.1.0/24 network. By default, if a router has no route to a destination, it will drop the packet. Therefore, the packet will be dropped.

Answer

eth0

Answer

lo

Answer

eth1

Question 13

Based on a network capture that shows a TCP connection to port 80 between 10.0.0.1 and 10.0.0.3, which of the following statements is correct?

Accepted Answer

All of the above. Based on the capture (which shows a TCP connection to port 80), the three-way handshake (SYN, SYN-ACK, ACK) is used, the client 10.0.0.1 uses a random high ephemeral port, and the server 10.0.0.3 responds on port 80, indicating an HTTP server. Thus, all three statements (A, C, D) are true, making 'All of the above' correct.

Answer

The three-way handshake is complete for a TCP connection

Answer

The client is using a random high port

Answer

The server 10.0.0.3 is running an HTTP server

Question 14

After rebooting, the bridge br0 does not forward traffic between eth0 and eth1. Which configuration is most likely missing?

Accepted Answer

bridge_fd 0. The bridge br0 is not forwarding traffic because the default bridge forward delay (bridge_fd) is too long, causing the bridge to remain in a blocking state while waiting for STP convergence. Setting bridge_fd 0 disables the forward delay, allowing the bridge to start forwarding immediately after boot. This is essential when STP is not needed or when the bridge must be operational without delay.

Answer

bridge_stp on

Answer

bridge_maxwait 10

Answer

up ip link set br0 up

Question 15

A Linux router is experiencing asymmetric routing issues. The network has two internet connections (ISP1 and ISP2) with default routes. The administrator wants to ensure that traffic originating from a specific source IP uses ISP1 for both incoming and outgoing packets. Which ip rule configuration achieves this?

Accepted Answer

ip rule add from 10.0.0.10 table isp1; ip route add default via 1.1.1.1 table isp1; sysctl -w net.ipv4.conf.all.rp_filter=0. It creates a policy routing rule that matches traffic from source IP 10.0.0.10 and directs it to a custom routing table named 'isp1', which contains a default route via ISP1's gateway (1.1.1.1). Additionally, disabling reverse path filtering (rp_filter=0) is essential to allow asymmetric routing — without it, the kernel would drop return packets arriving via a different interface than the one used for outgoing traffic, which is exactly the scenario in asymmetric routing.

Answer

ip rule add from 10.0.0.10 to 0/0 table isp1; ip route add default via 1.1.1.1 table isp1; ip rule add to 10.0.0.10 table isp1

Answer

ip rule add from 10.0.0.10 table isp1; ip route add default via 1.1.1.1 table isp1

Answer

ip rule add from 10.0.0.10 table isp1; ip route add default via 1.1.1.1