CCNA Networking Questions

resolvectl query is the native client for systemd-resolved. It sends the query through the resolver daemon, showing the answer, the link used, and the DNS server that responded. This isolates DNS resolution from nsswitch.conf sources like /etc/hosts, which is exactly what is needed to confirm the configured resolver can resolve the name.

systemd-resolved reads DNS server settings from resolved.conf, but applications reach it through /etc/resolv.conf. If that file is not symlinked to the stub or full resolv.conf generated by systemd-resolved, the configured servers are ignored. Recreating the symlink ensures queries go through systemd-resolved and reach 10.0.0.53.

The ip command from iproute2 is the current standard for network configuration and inspection. ip addr show lists every interface with its operational state, MAC address, and assigned IPv4/IPv6 addresses, which is precisely the information requested. The other commands either show unrelated data or belong to deprecated tooling.

Enabling `net.ipv4.ip_forward = 1` allows the Linux kernel to forward IP packets between network interfaces, which is required for a server to route traffic between the 10.0.1.0/24 and 10.0.2.0/24 subnets. Without this parameter, the kernel drops any packet not destined for the local system, preventing inter-network communication.

To direct traffic for a specific directly attached network out a particular interface and use a specific source address, the ip route add command with the dev and src options is used. This ensures packets to 10.0.0.0/24 leave via eth1 with source 10.0.0.10, fulfilling the requirement without affecting other traffic.

Static IP configuration requires editing the ifcfg file, restarting network, and verification.

The ip addr show command is the standard modern tool for displaying interface addresses, netmasks, and states. It is part of iproute2 and provides both IPv4 and IPv6 details in a structured format. The other commands either show routing tables, socket statistics, or rely on deprecated tools that do not present the requested information in the required format.

`firewall-cmd --list-all-zones` displays the firewall rules for all zones configured in firewalld, showing services, ports, and rules per zone. Option E is correct because `firewall-cmd --list-all` lists the rules for the default zone, providing a concise view of active firewall configuration. Both commands are native to firewalld and directly query its runtime and permanent rules via D-Bus.

/etc/resolv.conf is the primary configuration file for DNS resolver settings on RHEL/CentOS systems. It specifies the nameserver IP addresses, search domains, and resolver options used by the system's glibc resolver library to perform DNS lookups. Without this file, domain name resolution will fail, making it essential for network interface configuration.

The `ifup eth0` command reads the configuration file for the eth0 interface (typically `/etc/sysconfig/network-scripts/ifcfg-eth0` on RHEL/CentOS) and applies the settings (IP address, netmask, gateway, etc.) without requiring a system reboot. This is the standard way to activate a network interface with its configured parameters on Linux systems using the legacy network scripts.

The correct approach uses 'nmcli con mod' to alter the existing connection profile's IPv4 settings and set the method to manual, then brings the connection up to apply the changes. This persists the static address and gateway in NetworkManager's configuration, satisfying the reboot requirement. Lower-level ip commands are temporary and do not modify profiles, while creating a duplicate profile or using an invalid command would not achieve the goal.

The `nslookup -type=soa` command queries the DNS for the Start of Authority (SOA) record of a domain. The `-type=soa` flag explicitly sets the query type to SOA, which returns authoritative information about the zone, including the primary name server and administrator email.

In bonding mode 1 (active-backup), only one NIC is active at a time while the other remains in standby. When the active NIC fails, the bonding driver automatically fails over to the backup NIC by reassigning the MAC address and IP to the backup interface, typically within a few milliseconds. This ensures minimal interruption to network traffic without requiring manual intervention.

Temporary address changes are made directly in the kernel with the iproute2 ip addr add command. This affects the running system only and is lost on reboot, which is exactly what the migration test requires. Persistent configuration tools such as NetworkManager profiles or network configuration files would write the change to disk and reapply it at boot.

For a Linux router to forward traffic between interfaces, IP forwarding must be enabled, and the FORWARD chain must permit the traffic. Even with MASQUERADE configured, if either condition is not met, packets will be dropped. The administrator should verify net.ipv4.ip_forward and ensure FORWARD rules allow traffic from the internal to external interface.

Correct matches: service manages processes, socket handles socket activation, timer schedules events, target groups units. Common confusion: mixing socket and timer responsibilities is typical.

The `host` command is a simple DNS lookup utility that queries DNS servers to resolve a hostname to an IP address. It directly performs forward DNS resolution using the system's configured resolvers and returns the A or AAAA record for the given name.

The `ss -tln` command displays listening TCP sockets by using the `-t` flag for TCP, `-l` for listening sockets, and `-n` to show numeric addresses and ports without resolving service names. It reads socket information directly from the kernel's netlink interface, making it the modern replacement for netstat on Linux systems.

The correct line is 'nameserver 8.8.8.8'. The resolver reads nameserver entries in order, so placing it at the top makes it the first server used. The other options use invalid keywords or syntax that would not be recognized by the resolver.

The `ss -tlnp` command displays listening (`-l`) TCP (`-t`) sockets with numeric addresses (`-n`) and the associated process (`-p`), which directly confirms that a service is bound to TCP port 8080 on a specific interface (e.g., 0.0.0.0:8080 or 192.168.1.10:8080). This ensures the service is listening on the correct interface and is reachable from remote hosts.

For internal clients to reach the internet through a router, their private source addresses must be translated to the router's public address. This is done with a MASQUERADE rule in the nat table's POSTROUTING chain, applied to packets leaving the external interface. The other options either use the wrong chain, only permit forwarding without translation, or masquerade in the wrong direction.