ipconfig vs ifconfig – IP Configuration Commands for Windows and Linux

1. What Are ipconfig and ifconfig?

ipconfig and ifconfig are command-line utilities that let you view and manage the IP configuration of network interfaces on a host. They are the first tools any network engineer reaches for when diagnosing a connectivity problem — before pinging, before tracing a route, before anything else. If the host does not have a valid IP address, subnet mask, and default gateway, nothing else will work.

Despite serving the same diagnostic purpose, the two tools exist on different operating systems, use different syntax, and have different capabilities. ipconfig is the Windows standard; ifconfig is the traditional Unix/Linux/macOS tool, largely superseded on modern Linux by the ip command from the iproute2 package.

Aspect	ipconfig (Windows)	ifconfig (Linux / macOS)	ip command (Modern Linux)
Platform	Windows (all versions)	Linux, macOS, BSD Unix	Linux (replaces ifconfig)
Package / Origin	Built into Windows	`net-tools` package (legacy)	`iproute2` package (modern standard)
Primary Function	View IP settings; release and renew DHCP leases; flush DNS cache	View interfaces; assign IPs; bring interfaces up/down	Full interface and routing management — superset of ifconfig
Can Assign IP?	No (read + DHCP management only)	Yes — `ifconfig eth0 192.168.1.10 netmask 255.255.255.0`	Yes — `ip addr add 192.168.1.10/24 dev eth0`
Status on Modern Systems	Current — still the standard on all Windows versions	Deprecated on most Linux distros; not installed by default	Current standard — use this for all new Linux work

2. Windows — ipconfig Command Reference

Run all ipconfig commands from a Command Prompt (cmd.exe) or PowerShell. No elevated privileges are needed for read-only commands; DHCP and flush operations may require running as Administrator.

Command	What It Does	When to Use It
`ipconfig`	Displays the IPv4 address, subnet mask, and default gateway for each active adapter. The quickest sanity check.	First step in any Windows connectivity diagnosis — verify the host has a valid IP and gateway
`ipconfig /all`	Full detail: adds DHCP server address, lease obtained/expires timestamps, DNS servers, Physical Address (MAC), DHCP enabled flag, IPv6 address, and autoconfiguration address	When you need to confirm DHCP server identity, check lease expiry, verify DNS servers, or read the MAC address
`ipconfig /release`	Sends a DHCPRELEASE message to the DHCP server, surrendering the current lease. The adapter address drops to 0.0.0.0.	Before requesting a new IP; resolving IP address conflicts; moving to a different DHCP scope
`ipconfig /renew`	Sends a DHCPREQUEST or DHCPDISCOVER to obtain a new IP address lease from the DHCP server	After `/release`; after fixing a DHCP server issue; when the host has an APIPA address (169.254.x.x)
`ipconfig /flushdns`	Clears the Windows DNS resolver cache — removes all cached DNS entries, both positive (successful lookups) and negative (failed lookups)	After a DNS record change that is not yet reflected in responses; when a host resolves to a stale/incorrect IP; clearing a negative cache entry after fixing a DNS problem
`ipconfig /displaydns`	Shows the current contents of the local DNS resolver cache — every hostname the system has recently resolved, with TTL remaining	Confirming which IP a hostname resolves to locally; checking whether a DNS flush is needed; DNS troubleshooting
`ipconfig /registerdns`	Forces a dynamic DNS registration — re-registers the host's name and IP with the DNS server	After an IP change when the DNS record has not updated; Active Directory environments where dynamic DNS registration is used

ipconfig /all — Annotated Output

  C:\> ipconfig /all

  Windows IP Configuration

     Host Name . . . . . . . . . . . . : DESKTOP-JOHN       ← Computer name
     Primary Dns Suffix  . . . . . . . :
     Node Type . . . . . . . . . . . . : Hybrid
     IP Routing Enabled. . . . . . . . : No
     WINS Proxy Enabled. . . . . . . . : No

  Ethernet adapter Ethernet:

     Connection-specific DNS Suffix  . :
     Description . . . . . . . . . . . : Intel(R) Ethernet Connection  ← NIC model
     Physical Address. . . . . . . . . : 00-1A-2B-3C-4D-5E             ← MAC address
     DHCP Enabled. . . . . . . . . . . : Yes                            ← Dynamic IP
     Autoconfiguration Enabled . . . . : Yes
     IPv4 Address. . . . . . . . . . . : 192.168.1.100(Preferred)       ← IP address
     Subnet Mask . . . . . . . . . . . : 255.255.255.0                  ← /24 network
     Lease Obtained. . . . . . . . . . : Monday, 16 March 2026 08:00    ← DHCP lease start
     Lease Expires . . . . . . . . . . : Tuesday, 17 March 2026 08:00   ← Lease expiry
     Default Gateway . . . . . . . . . : 192.168.1.1                    ← Router IP
     DHCP Server . . . . . . . . . . . : 192.168.1.1                    ← DHCP server
     DNS Servers . . . . . . . . . . . : 8.8.8.8                        ← Primary DNS
                                         8.8.4.4                        ← Secondary DNS
     NetBIOS over Tcpip. . . . . . . . : Enabled

3. Linux / macOS — ifconfig Command Reference

ifconfig is part of the legacy net-tools package. On modern Debian/Ubuntu systems it is no longer installed by default (sudo apt install net-tools to restore it). For new work, always prefer the ip command — but ifconfig remains widely encountered and is still tested on the CCNA.

Command	What It Does	When to Use It
`ifconfig`	Lists all currently active (UP) interfaces with their IP addresses, netmask, broadcast address, MAC, MTU, and packet counters	Quick check of active interfaces and their addresses
`ifconfig -a`	Shows all interfaces — including those in the DOWN state that would be hidden by plain `ifconfig`	Checking whether an interface exists but is down; diagnosing a missing interface
`ifconfig eth0`	Displays configuration for the specific named interface only	Focused inspection of one interface without scrolling through all
`sudo ifconfig eth0 up`	Brings the named interface to the UP/active state	Enabling a disabled interface; recovering from accidental shutdown
`sudo ifconfig eth0 down`	Shuts down the named interface — takes it offline	Before changing its configuration; isolating a suspect interface during troubleshooting
`sudo ifconfig eth0 192.168.1.50 netmask 255.255.255.0`	Assigns a static IP address and subnet mask to the interface. Change is temporary — lost on reboot unless persisted in config files.	Quick temporary address assignment in a lab or for testing

ifconfig — Annotated Output

  $ ifconfig

  eth0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
  │     │                                             └─ MTU: max frame size in bytes
  │     └─ Interface flags: UP=active, BROADCAST=supports broadcast,
  │        RUNNING=driver loaded, MULTICAST=supports multicast
  └─ Interface name

        inet 192.168.1.100  netmask 255.255.255.0  broadcast 192.168.1.255
        │                   │                      └─ Broadcast address for this subnet
        │                   └─ Subnet mask (/24)
        └─ IPv4 address

        inet6 fe80::1c3b:22ff:fe4b:a8e3  prefixlen 64  scopeid 0x20<link>
        └─ IPv6 link-local address (fe80::/10 range, not routable off-link)

        ether 00:1c:42:4b:a8:e3  txqueuelen 1000  (Ethernet)
        │                        └─ Transmit queue length
        └─ MAC address (Layer 2 hardware address)

        RX packets 84231  bytes 102457890 (97.7 MiB)   ← Received packet/byte counters
        RX errors 0  dropped 0  overruns 0  frame 0    ← Error counters (should all be 0)
        TX packets 61204  bytes 8743210 (8.3 MiB)      ← Transmitted counters
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

4. Modern Linux — The ip Command (iproute2)

The ip command from the iproute2 suite is the current standard on all modern Linux distributions. It is more powerful, more consistent, and more scriptable than ifconfig. The CCNA exam increasingly references it alongside ifconfig.

Task	Legacy ifconfig Command	Modern ip Command
Show all interfaces and IPs	`ifconfig -a`	`ip addr show` or `ip a`
Show one interface	`ifconfig eth0`	`ip addr show eth0`
Bring interface up	`sudo ifconfig eth0 up`	`sudo ip link set eth0 up`
Bring interface down	`sudo ifconfig eth0 down`	`sudo ip link set eth0 down`
Assign static IP	`sudo ifconfig eth0 192.168.1.10 netmask 255.255.255.0`	`sudo ip addr add 192.168.1.10/24 dev eth0`
Remove IP address	`sudo ifconfig eth0 0.0.0.0`	`sudo ip addr del 192.168.1.10/24 dev eth0`
Show routing table	`route -n`	`ip route show` or `ip r`
Show link-layer (MAC) info	`ifconfig eth0` (includes ether line)	`ip link show eth0`

Note on DHCP with the ip command: The ip command itself does not handle DHCP — it only manages static addressing. To request a DHCP address on Linux, use sudo dhclient eth0 (ISC dhclient) or sudo dhcpcd eth0 depending on which DHCP client is installed. The DHCP client communicates with the server and then calls ip internally to set the received address.

5. Reading and Interpreting the Output Fields

Knowing what each field means is what turns raw command output into a diagnosis. These fields appear in both ipconfig /all and ifconfig / ip addr output, though under different labels.

Field	Windows Label	Linux Label	What It Means and Why It Matters
IPv4 Address	IPv4 Address	`inet`	The Layer 3 address assigned to this interface. If this shows 169.254.x.x (APIPA) or is missing entirely, the host cannot communicate on the network.
Subnet Mask	Subnet Mask	`netmask` (ifconfig) / prefix length e.g. `/24` (ip)	Defines which part of the IP address is the network and which is the host. A mismatch with other hosts on the same segment prevents communication even if IPs appear correct.
Default Gateway	Default Gateway	`ip route show` (default via x.x.x.x)	The router IP for sending traffic off the local subnet. If this is missing or wrong, the host can communicate locally but cannot reach any other network or the internet.
MAC Address	Physical Address	`ether`	The Layer 2 hardware address burned into the NIC. Used by ARP to map IPs to hardware. Helps identify the specific NIC when troubleshooting hardware issues.
DHCP Enabled	DHCP Enabled: Yes/No	No direct equivalent — inferred from whether a DHCP client assigned the address	Confirms whether the address was assigned dynamically or configured statically. Unexpected "No" means someone set a static IP — which may conflict with the DHCP range.
DHCP Server	DHCP Server	Seen in DHCP client logs (`journalctl`)	The IP of the server that granted the lease. Useful for confirming the correct DHCP server responded — a rogue DHCP server would show an unexpected IP here.
DNS Servers	DNS Servers	`/etc/resolv.conf` (`nameserver` lines)	The servers used for hostname resolution. If wrong or unreachable, hostnames won't resolve even though IP connectivity may be fine.
IPv6 Address	IPv6 Address / Link-local IPv6 Address	`inet6`	The `fe80::` link-local address is always present on any active interface. A full global unicast IPv6 address (2000::/3) indicates IPv6 connectivity beyond the local link.
Lease Obtained / Expires	Lease Obtained / Lease Expires	DHCP client logs	Shows when the DHCP lease was granted and when it will expire. A lease about to expire, or one that expired in the past and was not renewed, can cause intermittent connectivity loss.
Interface Status	Media State: Connected / Media disconnected	flags: UP/DOWN; RUNNING	"Media disconnected" (Windows) or missing the UP/RUNNING flags (Linux) means the physical or logical link is down — check the cable, port, and NIC before investigating anything else.

6. DHCP Release and Renew — How It Works

Understanding what actually happens during a release/renew cycle is a CCNA exam topic and essential for real-world DHCP troubleshooting.

  ipconfig /release                    ipconfig /renew
       │                                    │
       ▼                                    ▼
  Client sends DHCPRELEASE           Client sends DHCPDISCOVER
  to DHCP server                     (broadcast — seeking any DHCP server)
       │                                    │
  Server marks IP as available       Server replies DHCPOFFER
       │                             (offers an IP address)
  Client IP → 0.0.0.0                     │
  (no connectivity)              Client sends DHCPREQUEST
                                  (formally requesting the offered IP)
                                          │
                                  Server sends DHCPACK
                                  (confirms the lease)
                                          │
                                  Client configures IP, mask, gateway, DNS
                                  (connectivity restored)

On Linux, the equivalent is:

  Release:  sudo dhclient -r eth0        (sends DHCPRELEASE, removes address)
  Renew:    sudo dhclient eth0           (runs full DORA: Discover, Offer, Request, Ack)

When to use release/renew: If a host has an APIPA address (169.254.x.x) — meaning the DHCP server did not respond — try ipconfig /renew after confirming the DHCP server is reachable and the network connection is physically up. Do not release/renew repeatedly in quick succession — it can cause the DHCP server to exhaust its address pool with phantom leases on some implementations.

7. APIPA — Automatic Private IP Addressing (169.254.x.x)

APIPA (Automatic Private IP Addressing) is the Windows mechanism (defined in RFC 3927 as "link-local addressing") that automatically assigns an address in the 169.254.0.0/16 range when a host is configured for DHCP but cannot reach a DHCP server.

  Host boots → DHCP Discover sent (broadcast) →
      No DHCP server responds within timeout →
          Windows auto-assigns 169.254.x.x /16
          (x.x is randomly chosen; host verifies uniqueness via ARP probe)

  Result: Host has an IP — but it is only usable for
          communication with OTHER hosts on the same segment
          that also have 169.254.x.x addresses.
          No gateway, no DNS, no internet access.

Indicator	What It Tells You	What to Check
169.254.x.x address in ipconfig	The host did not receive a DHCP response — it fell back to APIPA	Physical connection (cable/Wi-Fi); DHCP server availability; DHCP scope exhaustion; correct VLAN/subnet reachability to DHCP server
0.0.0.0 address in ipconfig	DHCP release was performed and no new lease has been obtained yet	Run `ipconfig /renew`
Static IP outside expected range	DHCP is disabled and a manually configured IP is in use	Verify whether static addressing is intentional; check for conflicts with the DHCP pool range

Linux assigns a similar 169.254.x.x link-local address via the zeroconf / avahi mechanism when no DHCP response is received, though behaviour varies by distribution and configuration.

8. DNS Cache — ipconfig /flushdns and /displaydns

Windows maintains a local DNS resolver cache to speed up repeated lookups. Every hostname-to-IP resolution is stored here, along with its remaining TTL. This cache can become a source of problems when DNS records change.

Command	Effect	Typical Scenario
`ipconfig /displaydns`	Prints every cached DNS entry — hostname, record type, TTL remaining, and resolved IP	Confirming what IP a hostname resolves to locally; checking whether a stale entry is causing connectivity to the wrong server
`ipconfig /flushdns`	Empties the entire DNS resolver cache immediately. The next lookup for any hostname goes directly to the DNS server.	A website moved to a new IP but the old IP is still cached; a DNS record was corrected but the fix isn't visible yet; clearing a negative cache entry (NXDOMAIN) after adding a record

The Linux equivalent is service-dependent. For systemd-resolved (most modern distros): sudo resolvectl flush-caches. For nscd: sudo nscd -i hosts.

9. ipconfig vs ifconfig — Side-by-Side Comparison

Feature	ipconfig (Windows)	ifconfig (Linux/macOS)
View active interfaces	`ipconfig`	`ifconfig`
View all details including MAC and DNS	`ipconfig /all`	`ifconfig -a` (partial); full DNS in `/etc/resolv.conf`
Show down interfaces	`ipconfig /all` (shows "Media disconnected")	`ifconfig -a`
Release DHCP lease	`ipconfig /release`	`sudo dhclient -r eth0`
Renew DHCP lease	`ipconfig /renew`	`sudo dhclient eth0`
Flush DNS cache	`ipconfig /flushdns`	`sudo resolvectl flush-caches` (systemd-resolved)
Assign static IP	Not possible via ipconfig — use Network Settings GUI or netsh	`sudo ifconfig eth0 x.x.x.x netmask y.y.y.y`
Bring interface up/down	Not possible via ipconfig — use Device Manager or netsh	`sudo ifconfig eth0 up/down`
View routing table	`route print` or `netstat -r`	`route -n` or `ip route show`
Output style	One block per adapter with labelled fields — human-readable	One block per interface with condensed technical fields

10. Troubleshooting Workflow — Step-by-Step

A structured approach to diagnosing connectivity problems using these tools. Work from the bottom of the OSI stack upward — confirm Layer 1 and Layer 2 before blaming Layer 3.

PROBLEM: Host cannot reach the internet or a remote host
═══════════════════════════════════════════════════════

Step 1 — Check the IP assignment
─────────────────────────────────
Windows: ipconfig
Linux: ip addr show (or ifconfig)

┌─ 169.254.x.x? → APIPA — DHCP server not reachable
│ Fix: Check cable/Wi-Fi; run ipconfig /renew; verify DHCP server is up
├─ 0.0.0.0? → No IP at all — interface may be down or DHCP released
│ Fix: ipconfig /renew (Windows) or sudo dhclient eth0 (Linux)
├─ Wrong subnet (e.g. 10.0.0.x when expecting 192.168.1.x)? → Wrong DHCP scope
│ or rogue DHCP server. Check ipconfig /all for DHCP Server field.
└─ Correct IP? → Proceed to Step 2

Step 2 — Verify the default gateway
─────────────────────────────────────
Windows: ipconfig (Default Gateway field)
Linux: ip route show (look for "default via x.x.x.x")

┌─ Gateway missing or 0.0.0.0? → Host can communicate locally
│ but cannot reach any other subnet or the internet
│ Fix: Check DHCP server gateway option; set static route if needed
└─ Gateway present? → Ping it: ping 192.168.1.1
┌─ Ping fails? → Layer 1/2 issue (cable, port, VLAN) or firewall
└─ Ping succeeds? → Local network OK; proceed to Step 3

Step 3 — Verify DNS
────────────────────
Windows: ipconfig /all (DNS Servers field)
ipconfig /displaydns (check cache for stale entries)
Linux: cat /etc/resolv.conf (nameserver lines)

┌─ DNS servers missing? → DHCP did not push DNS; configure manually
├─ DNS servers present but names don't resolve? → Test DNS directly:
│ nslookup google.com 8.8.8.8
│ If this works but normal resolution doesn't → DNS server unreachable
│ or incorrect server configured
└─ Stale DNS cache? → ipconfig /flushdns (Windows)
sudo resolvectl flush-caches (Linux)

Step 4 — Check interface status
─────────────────────────────────
Windows: ipconfig /all (Media State: Connected / Media disconnected)
Linux: ip link show (look for UP and LOWER_UP flags)

┌─ Media disconnected / interface DOWN? → Physical problem
│ Check: cable seated; switch port active; NIC driver installed
└─ Interface UP but problems persist? → Suspect misconfiguration
or upstream network issue — use ping and traceroute next

11. Example Scenario — Full Diagnosis

John cannot browse the internet from his Windows laptop. He opens Command Prompt and works through the steps above.

  C:\> ipconfig

  Ethernet adapter Ethernet:
     IPv4 Address. . . . : 169.254.34.201    ← APIPA address — DHCP failed!
     Subnet Mask . . . . : 255.255.0.0
     Default Gateway . . :                   ← No gateway (APIPA never gets one)

  Diagnosis: DHCP server not responding. Check physical connection first.

  C:\> ipconfig /all
  ...
     Media State . . . . : Media connected   ← Cable is plugged in
     DHCP Enabled . . . . : Yes
     DHCP Server . . . . :                   ← No DHCP server was found

  Physical connection OK. DHCP server unreachable.
  John checks the switch — port LED is off. He re-seats the cable.
  Port LED lights up. He then runs:

  C:\> ipconfig /renew

  Renewing the IP address for Ethernet...
  Ethernet adapter Ethernet:
     IPv4 Address. . . . : 192.168.1.105     ← Valid DHCP address obtained
     Subnet Mask . . . . : 255.255.255.0
     Default Gateway . . : 192.168.1.1       ← Gateway restored

  Internet connectivity restored. Root cause: loose cable at the switch.

12. Exam Tips & Key Points

ipconfig is the Windows IP configuration tool; ifconfig is the legacy Linux/macOS equivalent; ip addr is the modern Linux standard.
ipconfig /all is the most information-rich Windows command — it shows MAC address, DHCP server, lease times, and DNS servers that plain ipconfig omits.
ipconfig /release then ipconfig /renew forces a full DHCP cycle — release sends DHCPRELEASE; renew runs the full DORA (Discover, Offer, Request, Ack) sequence.
A 169.254.x.x address always means APIPA — the host could not reach a DHCP server. The device has no gateway and no DNS; it can only communicate with other APIPA hosts on the same segment.
ipconfig /flushdns clears the Windows DNS cache — use it when a DNS record has been updated but the host still resolves to the old IP.
On Linux, ifconfig -a shows all interfaces including those in the DOWN state; plain ifconfig only shows UP interfaces.
The ip command replaces both ifconfig (use ip addr) and route (use ip route). Know both for the CCNA exam.
MAC address is labelled Physical Address in ipconfig /all output and ether in ifconfig output.
A missing default gateway means the host can ping local subnet hosts but cannot reach anything beyond the local network — a classic exam scenario.

13. Summary

Aspect	Detail
Windows IP command	`ipconfig` (basic) / `ipconfig /all` (full detail)
Linux/macOS IP command	`ifconfig` (legacy) / `ip addr show` (modern)
DHCP release (Windows)	`ipconfig /release` → sends DHCPRELEASE; IP drops to 0.0.0.0
DHCP renew (Windows)	`ipconfig /renew` → runs DORA sequence; obtains new lease
DNS cache flush (Windows)	`ipconfig /flushdns`
APIPA address range	169.254.0.0/16 — assigned when DHCP fails; no gateway, no DNS
MAC address label	Physical Address (Windows) / ether (Linux ifconfig)
Show all Linux interfaces	`ifconfig -a` or `ip addr show`
Bring Linux interface up	`sudo ifconfig eth0 up` or `sudo ip link set eth0 up`
First troubleshooting step	Run `ipconfig` / `ip addr` to confirm valid IP, mask, and gateway before any other diagnostic

IP Configuration Commands Quiz

1. Which command displays the current IP configuration on a Windows host?

A. ipconfig — the Windows built-in command for viewing and managing IP configuration B. ifconfig — the Linux/macOS equivalent that does not exist on Windows C. netstat — shows active connections and ports, not IP configuration D. traceroute — traces the path to a remote host, not local IP config

Correct answer is A. ipconfig is the Windows command-line utility for displaying and managing IP network configuration. Running it without options shows the IPv4 address, subnet mask, and default gateway for each active adapter — the three pieces of information needed to verify basic connectivity. ifconfig serves the same purpose on Linux and macOS but is not available on Windows. netstat and traceroute/tracert are diagnostic tools that presuppose a working IP configuration.

2. On Linux or macOS, which command shows active network interfaces and their IP addresses?

A. ipconfig — the Windows-only tool; does not exist on Linux or macOS B. ifconfig — the traditional Linux/macOS command for viewing and configuring network interfaces C. netsh — a Windows network configuration tool not available on Linux D. nslookup — a DNS query tool, not a network interface viewer

Correct answer is B. ifconfig is the traditional Unix/Linux/macOS tool for viewing and configuring network interfaces. Running it without arguments displays all currently active (UP) interfaces with their IPv4 address, netmask, broadcast address, IPv6 link-local address, MAC address, MTU, and packet counters. Note: on modern Linux distributions, ifconfig from the net-tools package is deprecated and may not be installed by default — ip addr show from iproute2 is the preferred replacement.

3. Which ipconfig option releases the current DHCP-assigned IP address on Windows?

A. /renew — requests a new IP from the DHCP server (the opposite operation) B. /flushdns — clears the DNS resolver cache, not the DHCP lease C. /release — sends a DHCPRELEASE message to the server and sets the adapter address to 0.0.0.0 D. /all — displays full configuration details but does not change any settings

Correct answer is C. ipconfig /release instructs the Windows DHCP client to send a DHCPRELEASE message to the DHCP server, formally relinquishing the current IP address lease. The adapter's IP address is immediately set to 0.0.0.0 and the host loses network connectivity. The DHCP server marks the address as available for reassignment. This is typically followed by ipconfig /renew to obtain a new lease — useful when resolving IP conflicts, moving to a different DHCP scope, or forcing a refresh of DHCP options like DNS server addresses.

4. What does ipconfig /renew do, and what DHCP process does it trigger?

A. It releases the current lease and sets the IP to 0.0.0.0 B. It brings the network adapter up from a disabled state C. It displays the full IP configuration including MAC and DNS servers D. It requests a new IP address lease from a DHCP server, triggering the DHCP DORA process (Discover, Offer, Request, Ack)

Correct answer is D. ipconfig /renew causes the Windows DHCP client to initiate a new lease request. If the current lease has been released (IP is 0.0.0.0), it sends a DHCPDISCOVER broadcast to locate any available DHCP server. If a lease exists, it may send a DHCPREQUEST directly to the current DHCP server to renew it. The server responds with a DHCPOFFER (or DHCPACK for renewal), the client accepts with DHCPREQUEST, and the server confirms with DHCPACK — the full DORA sequence. The client then configures the assigned IP address, subnet mask, default gateway, and DNS servers.

5. Which command shows all network interfaces on Linux — including those that are currently down?

A. ifconfig -a — the -a flag instructs ifconfig to display all interfaces regardless of their UP/DOWN state B. ipconfig /all — the Windows full-detail command; not available on Linux C. ip link show — also shows all interfaces, but is the modern iproute2 equivalent D. netstat -i — shows interface statistics but not full address configuration

Correct answer is A. Plain ifconfig only lists interfaces that are currently in the UP state — an interface that has been brought down or never configured will be invisible. The -a flag forces ifconfig to show all interfaces regardless of state. This is important when diagnosing why a device is not communicating — the interface may exist but be in the DOWN state. Note that option C (ip link show) achieves the same result using the modern iproute2 tool and is equally correct in practice — the question specifically asks about the ifconfig equivalent.

6. What is the modern Linux command that has replaced ifconfig for displaying IP addresses?

A. netstat — shows network connections and statistics, not a replacement for ifconfig B. ip addr show (ip a) — from the iproute2 package; the current standard for viewing and managing addresses on Linux C. route — shows the routing table; replaced by ip route, not ip addr D. arp — displays the ARP cache; not a replacement for ifconfig

Correct answer is B. The ip command from the iproute2 package is the modern replacement for the entire net-tools suite (ifconfig, route, arp, netstat). For IP address management specifically, ip addr show (abbreviated ip a) replaces ifconfig. It shows all interfaces and their addresses by default (equivalent to ifconfig -a). The iproute2 package is pre-installed on virtually all modern Linux distributions; net-tools containing ifconfig must be installed separately on many distros and is considered deprecated.

7. A Windows host shows an IP address of 169.254.14.7 in ipconfig output. What does this indicate and what should you check first?

A. The host has been assigned a valid static IP from the 169.254.0.0 range by the administrator B. The host is configured as a DHCP server and is reserving this address for a client C. APIPA — the host could not reach a DHCP server and self-assigned a link-local address; check the physical connection and DHCP server availability D. The host is using IPv6 link-local addressing converted to IPv4 notation

Correct answer is C. The 169.254.0.0/16 range is reserved for APIPA (Automatic Private IP Addressing), defined in RFC 3927. Windows automatically assigns an address in this range when it is configured for DHCP but receives no DHCPOFFER within the timeout period. An APIPA address means the host has no valid gateway and no DNS — it can only communicate with other APIPA hosts on the same segment. The first things to check are: (1) the physical connection — is the cable plugged in and the port LED active? (2) Is the DHCP server running and reachable? (3) Has the DHCP scope been exhausted? After fixing the root cause, run ipconfig /renew to obtain a proper lease.

8. In Windows ipconfig /all output, what label is used for the network adapter's MAC address?

A. Hardware Address — the Linux ifconfig label for the same field B. Ethernet Address — a generic term not used in Windows output C. Link Address — not a label used in any standard command output D. Physical Address — the exact label Windows uses in ipconfig /all output, displayed as XX-XX-XX-XX-XX-XX

Correct answer is D. Windows ipconfig /all labels the MAC address as Physical Address and displays it in hyphen-separated hexadecimal notation, e.g. 00-1A-2B-3C-4D-5E. In contrast, ifconfig on Linux labels it as ether and uses colon-separated notation, e.g. 00:1a:2b:3c:4d:5e. The ip link show command uses the label link/ether. All three refer to the same 48-bit Layer 2 hardware address burned into the NIC. Knowing the different labels across operating systems is a common CCNA exam question.

9. What does the subnet mask shown in ipconfig / ifconfig output define?

A. The IP address of the default gateway router B. Which bits of the IP address identify the network portion and which identify the individual host — determining which hosts are on the same local segment C. The addresses of the DNS servers to use for hostname resolution D. The range of MAC addresses assigned to this network segment

Correct answer is B. The subnet mask is a 32-bit value that divides an IP address into a network portion (the leading 1 bits) and a host portion (the trailing 0 bits). For example, a subnet mask of 255.255.255.0 (/24) means the first 24 bits identify the network and the last 8 bits identify the individual host. The host uses its IP address AND'd with the subnet mask to determine whether a destination is on the local segment (send directly via ARP) or on a remote network (send to the default gateway). A subnet mask mismatch between two hosts on the same physical segment will prevent communication even if their IPs appear to be in the same range.

10. A user reports that a website they updated yesterday still shows the old IP address when they try to visit it. Which command should they run first on their Windows machine?

A. ipconfig /flushdns — clears the local DNS resolver cache so the next lookup fetches the updated record from the DNS server B. ipconfig /release — releases the DHCP lease; unrelated to DNS records C. ipconfig /renew — requests a new IP address; does not affect DNS cache D. ipconfig /registerdns — re-registers this host's DNS record; does not clear the local cache of other hosts' records

Correct answer is A. Windows caches DNS query results locally to speed up repeated lookups. When a DNS record is updated (e.g., a website moves to a new server with a new IP), the old IP may remain in the local cache until its TTL expires — which could be hours or days. ipconfig /flushdns immediately empties the entire DNS resolver cache, forcing the next hostname lookup to go directly to the DNS server and fetch the current record. The user can verify the cached entry first with ipconfig /displaydns to confirm a stale entry exists before flushing. Options B and C affect DHCP, not DNS. Option D registers this machine's own hostname — it does not clear entries for other hostnames.

← Back to Home