IP Field KitTo install, tap Share, then Add to Home Screen.
Address lookup
Enter an IPv4 or IPv6 address to see its subnet, range, and what kind of address it is.
Subnet
Binary
Other formats
Owner
Special address ranges (IPv4 and IPv6)
Scan
Photograph a screen, label, or printout, or paste command output. The IP addresses are pulled out and labeled.
Text is read on this device and the photo never leaves it. The first scan downloads the text-recognition engine (about 7 MB). After that, scanning works offline.
IPv4 settings found
IPv6 settings found
Addresses found
No IPv4 addresses found in this text. If the photo was blurry or at an angle, try again closer and straight on, or fix the text above.
Device check
Enter a device's IPv4 or IPv6 settings to catch a wrong mask or prefix, a gateway outside the subnet, or a failed DHCP lease or missing router advertisement. Then run the tests below on the device.
Result
Test it on the device
The checks above only cover the settings. These commands test the real network. Run them on the device and compare what you get with the example output.
The device IP and gateway come from the fields at the top.
Reachability, step by step
Work down the list. The first test that fails shows where the problem is.
MTU and fragmentation
MTU is the largest packet a link carries. When a link on the path has a smaller MTU, big packets are split up or, with Don't Fragment set, dropped. Typical signs: ping works and small pages load, but large pages, HTTPS, VPNs, file copies, or remote desktop hang. Test to a host on the far side of the link you suspect, such as across the VPN.
To find the path MTU, start at 1500. If the test fails, lower the MTU by 10 until it passes, then raise it by 1 until it fails. The last MTU that passed is the path MTU. TCP's maximum segment size (MSS) is the MTU − 40.
See it in Wireshark
Capture while you run the ping tests, then type these in the filter bar above the packet list.
- Right-click
ip.lenordata.lenin the packet details and choose Apply as Column to see sizes at a glance. - Statistics → Packet Lengths shows how packet sizes are spread across the capture.
- Wireshark shows frames without the 4-byte checksum, so a full-size frame reads 1514 bytes, or 1518 with a VLAN tag.
- On the computer doing the capture, outgoing packets can show up far larger than the MTU, up to 64 KB. That's the network card's offloading, not a real packet on the wire. Turn it off with the command below, or capture from a switch mirror port.
Tunnel and label overhead
Every tunnel or label adds headers inside the same link MTU, leaving less room for data. Pick what's on the path. IPsec sizes are worst case, with maximum padding.
Work backward from a test
Router checks
Routes
Use these when the gateway answers but places beyond it don't, or when traffic leaves through the wrong connection. That's common with VPNs, and with Wi-Fi and Ethernet connected at the same time.
ARP
ARP finds the MAC address that goes with an IP on the local link. If the gateway has no ARP entry, the problem is at layer 2: the cable, switch port, VLAN, or Wi-Fi. ARP also exposes duplicate IP addresses.
See it in Wireshark
Find a device
Step-by-step help for reaching equipment when you don't know its IP address. Each step says what to do, what you'll see, and why it works. Work in order and stop as soon as you find it.
What you know so far
Step 1 · Get ready
- Connect your laptop straight to the device with an Ethernet cable, or plug both into the same small switch. Check that the link lights come on at both ends. A device powered over Ethernet (PoE) needs a PoE switch or injector.
- Turn off Wi-Fi from the taskbarTurn off Wi-Fi from the menu barTurn off Wi-Fi in your network settings so your laptop uses only the cable.
- Find the device's MAC address on its label. It's 12 hex digits, often marked MAC or HW, like 00:11:22:33:44:55.
Find the name of your laptop's wired connection:
Step 2 · Try the quick wins
Check the label and the manual
Many devices ship with a default address printed on the label or listed in the manual, such as 192.168.0.1, 192.168.1.1, or 10.0.0.1. If you have one, enter it below and go to step 5.
Let your laptop ask for an address
Set the wired connection to get an address automatically (DHCP), then:
Try the maker's discovery tool
Many cameras, recorders, PLCs, and access points have a free tool that finds them on the cable even when their IP doesn't match yours, for example Axis IP Utility, Hikvision SADP, Siemens PRONETA, or Rockwell's BOOTP/DHCP Server. Check the maker's support site.
Found it?
Then go to step 5 to connect.
Step 3 · Listen for it with Wireshark
Open Wireshark and double-click your wired interface, , to start capturing. Then power-cycle the device, or unplug its cable for a few seconds and plug it back in. Type each filter into the bar above the packet list and press Enter.
If you only saw ARP, start with a /24 prefix. It's the most common size for small networks and factory defaults.
Found it?
Then go to step 5 to connect.
Step 4 · If the device stays quiet
Devices set to a fixed address often send nothing until something talks to them. Try these in order.
Ask every IPv6 device to answer
Found the device's fe80:: address? Enter it in the "Found it?" box below. Step 5 then shows how to reach it over IPv6 with no address setup.
Sweep a common address range
Many devices ship in one of these ranges. Pick one, give your laptop an address in it, and sweep it.
Use the console port
Switches, routers, and firewalls usually have a console port (RJ-45 or USB) that works with no network settings at all.
Factory reset, as a last resort
Holding the reset button, usually for 10 to 30 seconds while powered, puts the device back to the address in its manual or to DHCP. It also erases its settings, so get permission first.
Found it?
Then go to step 5 to connect.
Step 5 · Connect
Shortcuts
Subnetting practice
Practice borrowing bits in IPv4 or IPv6. Enter a network and how many subnets or hosts you need, work the problem yourself, then check each step of the math and where the answer sits in the lookup tables. It's also handy for planning how to split a network.
Answer
The math
Lookup tables
Hosts table
Find the column where the new prefix lands. SM is the mask value for that octet, INC is the increment, and # is the addresses per subnet. Usable hosts = # − 2.
Subnets table
Each borrowed bit doubles the number of subnets and halves the addresses in each one.
Subnet ranges
- Usable hosts = 2h − 2 because the first address is the network ID and the last is the broadcast. /31 (point-to-point links, RFC 3021) and /32 (a single host) don't follow that rule, so the solver stops at /30.
- Subnets = 2n counts subnet zero and the all-ones subnet, which modern routers use. Some older courses use 2n − 2, so check which rule your exam expects.
Answer
The math
Lookup table
IPv6 subnet sizes
IPv6 subnets are usually planned on nibble boundaries, multiples of 4 bits, so each step is one hex digit: 16 times as many subnets, each 16 times smaller. The highlighted row is your answer; a shaded row is the nibble-boundary choice.
Subnet prefixes
- A LAN subnet in IPv6 is almost always a /64, so planning is about how many /64s you need. Sites usually get a /48 or a /56 from their provider.
- IPv6 has no broadcast address and no network-address rule. Every address in a subnet can go to a device, except a few reserved anycast addresses such as the all-zeros one.