192.168.100.21 Admin Login

192.168.100.21 is a Class C private IPv4 address belonging to the 192.168.100.0/24 subnet — a range closely associated with ISP-provisioned cable modems, modem-router combos, and broadband gateway devices from manufacturers such as ARRIS, Motorola, Huawei, Zyxel, Ubee, and Ambit Microsystems. Unlike the more familiar consumer subnets built around 192.168.1.254 or 192.168.0.1, the 192.168.100.x range is predominantly used by ISP-deployed hardware to avoid IP conflicts with customer-owned routers placed downstream. The primary default gateway in this subnet is 192.168.100.1, and 192.168.100.21 is the twenty-first host address within the same range. It is typically assigned to a connected device via DHCP — such as a laptop, smartphone, smart TV, or networked printer — or manually configured as a static IP for a specific piece of network equipment. Other common default gateways you may encounter include 192.168.0.1 and 10.0.0.1.

How to Access 192.168.100.21

To access a device or admin panel at 192.168.100.21, open your preferred web browser — Chrome, Firefox, Edge, or Safari — and type http://192.168.100.21 directly into the address bar, then press Enter. Do not type it into a search engine, as that will return search results rather than your device's login page. If 192.168.100.21 has been configured as the management interface of a device on your network, you will be presented with a login prompt asking for a username and password.

Because 192.168.100.21 is a private IP address, it is only reachable from within your local network. You must be connected to the same network — either via Wi-Fi or a wired Ethernet cable — as the device using this address. If you are trying to reach your ISP-supplied gateway (such as an ARRIS, Motorola, Huawei, or Zyxel modem-router), note that the default admin interface is most commonly found at 192.168.100.1, not at 192.168.100.21. However, if a network administrator or ISP technician has manually assigned 192.168.100.21 as the management address of a specific device, you can reach it using the steps above. Once logged in, you will have access to your device's configuration panel, where you can adjust Wi-Fi settings, manage connected devices, configure port forwarding, update firmware, and more — depending on the device type and manufacturer.

If You Can't Access 192.168.100.21

If typing http://192.168.100.21 into your browser does not load a login page, there are several possible reasons and solutions to try:

• Wrong gateway address: 192.168.100.21 is a host address, not a default gateway. If you are trying to reach your router or modem's admin panel, the correct address is most likely 192.168.100.1 for ARRIS, Motorola, Huawei, Zyxel, and Ubee devices. Try that address first.
• Not on the same subnet: Your computer must be on the 192.168.100.x subnet to reach 192.168.100.21. Open Command Prompt (Windows: Start > cmd, then type ipconfig) or Terminal (Mac/Linux: type ifconfig or ip a) and check your current IP address. If your IP starts with 192.168.1.x or 192.168.0.x, you are on a different subnet and cannot directly reach 192.168.100.21 without reconfiguring your network.
• No device assigned to this address: If no device on your network has been assigned or configured to use 192.168.100.21, the address will be unreachable. Check your router's DHCP client list to see which addresses are currently in use.
• Browser cache or HTTPS issue: Try clearing your browser cache or prefixing the address with http:// (not https://), as most router admin panels do not use SSL by default.
• Firewall blocking access: Some ISP-provisioned gateways, particularly those from Huawei and ARRIS, include built-in firewall rules that may restrict access to certain host addresses. Check your gateway's firewall settings at 192.168.100.1.

If you are still unable to connect, use our guide to find your router IP address and confirm the correct admin address for your specific device.

Router Brands That Use the 192.168.100.x Subnet

While 192.168.100.21 is not itself a default gateway address, it belongs to the 192.168.100.0/24 subnet that is strongly associated with a specific group of ISP-provisioned hardware manufacturers. If your device has been assigned 192.168.100.21, it is very likely connected to one of the following gateway types, all of which use 192.168.100.1 as their primary admin interface:

• ARRIS — ARRIS modem-router combos including the TG1672G, TG1682G, SBG6700-AC, and SBG8300 series commonly use 192.168.100.1 as their default gateway. Devices connected to these gateways — such as your computer or a network printer — may receive addresses like 192.168.100.21 via DHCP. ARRIS hardware is widely deployed by ISPs including Comcast/Xfinity, Cox, and Spectrum. Default credentials are typically admin / password or cusadmin / highspeed.
• Motorola — Motorola cable modems and modem-router gateways such as the SBG940, SURFboard MG7700, MG8702, and MT7711 series use 192.168.100.1 as the default admin IP. Connected devices on these networks are assigned addresses in the 192.168.100.x range, including 192.168.100.21. Default credentials are typically admin / motorola.
• Huawei — Huawei broadband gateways and ONT (Optical Network Terminal) devices, including the HG8245, HG8546, and EchoLife series, are deployed by ISPs across Asia, Europe, Africa, and the Middle East and frequently operate on the 192.168.100.x subnet. Huawei uses this range specifically to avoid conflicts with customer-owned routers that typically default to 192.168.1.x. Default credentials are typically admin / admin.
• Zyxel — Zyxel DSL modem-routers and ISP-provisioned gateways also operate within the 192.168.100.x subnet, with 192.168.100.1 as the primary admin interface. Zyxel devices are commonly deployed by European and Asian ISPs. Default credentials vary by model and are printed on the device label.
• Ubee — Ubee modem-router combos, frequently deployed by cable ISPs in North America and Europe, also use the 192.168.100.x subnet. If your device received 192.168.100.21 as its IP address and you have a Ubee gateway, your admin panel is at 192.168.100.1.
• Ambit Microsystems — Ambit (an OEM manufacturer for several ISPs) produces cable modem-router units that operate on the 192.168.100.x subnet. These devices are often unbranded or carry an ISP's own label, but the underlying hardware and default gateway remain consistent with this subnet.

Changing Your Router's Password

If your network operates on the 192.168.100.x subnet — as is common with ARRIS, Motorola, Huawei, Zyxel, Ubee, and Ambit modem-router combos — it is critical that you change your router's default admin password as soon as possible after setup. The default credentials for these devices are publicly documented and widely known, making your network vulnerable to unauthorized access if left unchanged.

To change your password, navigate to your router's admin panel at 192.168.100.1 and log in using the default credentials printed on your device's label. Once logged in, look for the Administration, Management, or Security section of the interface. From there, select the option to change your admin password. You will typically be prompted to enter your current password and then type your new password twice for confirmation. Choose a strong password that is at least 12 characters long and includes a mix of uppercase letters, lowercase letters, numbers, and special characters. Once saved, you will need to use your new password every time you access the admin panel from a device on the 192.168.100.x subnet — including from 192.168.100.21.

Router Username and Password List

What is 192.168.100.21 as a Private IP Address?

192.168.100.21 is a private IPv4 (Internet Protocol) address defined under RFC 1918, which means it is reserved exclusively for use within local area networks (LANs) and is never routed on the public internet. It falls within the 192.168.0.0/16 block — one of three private IP ranges — and more specifically within the 192.168.100.0/24 subnet, which accommodates up to 254 usable host addresses (192.168.100.1 through 192.168.100.254).

The 192.168.100.x subnet is particularly associated with ISP-provisioned hardware. Manufacturers like ARRIS, Motorola, Huawei, Zyxel, Ubee, and Ambit Microsystems deliberately chose this subnet for their cable modem and modem-router combo products to avoid IP address conflicts with the customer-owned routers that are often placed behind them. When your ISP installs a gateway device at your home or office, it typically claims 192.168.100.1 as its own address and then distributes addresses like 192.168.100.21 to the devices you connect to it.

Every device that connects to a network using the 192.168.100.x subnet receives its own unique private IP. For example, if you connect a laptop, a smartphone, and a tablet to a Motorola or ARRIS gateway in sequence, they might receive:

• The laptop gets the 192.168.100.21 private IP.
• The smartphone gets the 192.168.100.22 private IP.
• The tablet gets the 192.168.100.23 private IP.

These addresses are how the gateway knows where to send specific data packets it retrieves from the internet. The devices use them to communicate requests to the gateway, and from there — to the World Wide Web. It is important to note that printers, IP cameras, NAS drives, smart TVs, and gaming consoles will also receive private IPs like 192.168.100.21 once connected to the network. These addresses are the foundation of how your local network operates.

One last thing about the 192.168.100.21 private IP: if you are trying to use it to access your router's settings page and it is not working, it is most likely because 192.168.100.21 is a host address — not the gateway itself. The admin panel for ARRIS, Motorola, Huawei, Zyxel, and Ubee devices in this subnet is located at 192.168.100.1. If that address also fails, you may need to perform a factory reset to restore the default configuration.

Factory Reset Instructions for Devices on the 192.168.100.x Subnet

If you have lost access to your gateway's admin panel or forgotten your admin password, a factory reset will restore all settings — including the default gateway address of 192.168.100.1 and the original credentials — to their out-of-box state. Note that a factory reset will also erase all custom Wi-Fi names, passwords, port forwarding rules, and any other configurations you have made. Here is how to perform a factory reset on the most common brands associated with the 192.168.100.x subnet:

• ARRIS (TG1672G, TG1682G, SBG series): Locate the small recessed Reset button on the back or bottom of the device. Using a straightened paperclip or pin, press and hold the Reset button for at least 10–15 seconds until the device's lights flash or cycle. Release the button and wait 2–3 minutes for the device to fully reboot. Once complete, the gateway will be accessible again at 192.168.100.1 with the default credentials printed on the device label.
• Motorola (MG7700, MG8702, MT7711, SBG series): With the device powered on, press and hold the Reset button (usually on the rear panel) for 10 seconds using a pin or paperclip. The power LED will blink, indicating the reset is in progress. Wait approximately 2 minutes for the reboot to complete before attempting to access 192.168.100.1.
• Huawei (HG8245, HG8546, EchoLife ONTs): Press and hold the Reset button on the back of the device for 10 seconds. The indicator lights will turn off and then come back on as the device reboots. After 2–3 minutes, you can access the admin panel at 192.168.100.1 using the default credentials (typically admin / admin or the credentials printed on the device label).
• Zyxel (DSL and cable gateway models): Press and hold the Reset button for 10 seconds until the Power LED begins to blink. Release the button and allow the device to reboot fully (approximately 2 minutes). The admin panel will be restored at 192.168.100.1.
• Ubee (modem-router combos): Locate the Reset pinhole on the rear of the device. Insert a pin and hold for 10–15 seconds until the device restarts. After rebooting, access the admin panel at 192.168.100.1 with the default credentials from the device label.

After any factory reset, your connected devices — including those that previously held addresses like 192.168.100.21 — will need to re-request IP addresses from the gateway via DHCP. Simply disconnect and reconnect to the network, or run ipconfig /release followed by ipconfig /renew in the Windows Command Prompt.

Related IP Addresses in the 192.168.100.0/24 Subnet

The 192.168.100.0/24 subnet contains 254 usable host addresses. Here are the most notable addresses within this range that you are likely to encounter on networks managed by ARRIS, Motorola, Huawei, Zyxel, Ubee, and Ambit gateways:

• 192.168.100.1 — The default gateway and admin panel address for the entire 192.168.100.x subnet. This is the address used by ARRIS, Motorola, Huawei, Zyxel, Ubee, and Ambit modem-router combos. Always try this address first when attempting to access your ISP-provisioned gateway's settings.
• 192.168.100.2 – 192.168.100.20 — Host addresses in the lower range of the subnet, typically assigned by DHCP to the first devices that connect to the network, or reserved for static assignment to specific equipment such as network switches or access points.
• 192.168.100.21 — The current address on this page. A host address within the 192.168.100.x subnet, most commonly assigned via DHCP to a client device such as a laptop, smartphone, or smart TV connected to an ARRIS, Motorola, Huawei, Zyxel, or Ubee gateway.
• 192.168.100.22 – 192.168.100.99 — Additional host addresses in the mid-range of the subnet, available for DHCP assignment or static configuration to other connected devices on the same network.
• 192.168.100.100 – 192.168.100.199 — Frequently used as the DHCP pool range on ISP-provisioned gateways. Many ARRIS and Motorola devices are configured by ISPs to assign dynamic addresses starting from 192.168.100.100, leaving the lower addresses (including 192.168.100.21) available for static assignment.
• 192.168.100.200 – 192.168.100.254 — Upper host addresses in the subnet, sometimes reserved by ISP configurations for specific management or diagnostic purposes.
• 192.168.100.255 — The broadcast address for the 192.168.100.0/24 subnet. This address is not assignable to any device and is used to send data to all hosts on the subnet simultaneously.

If you are looking for other commonly used default gateway addresses outside this subnet, you may also want to explore 192.168.0.1, 192.168.8.1, 192.168.10.1, and 10.0.0.1.

Frequently Asked Questions About 192.168.100.21

Is 192.168.100.21 a router's default gateway?

No. 192.168.100.21 is not a standard default gateway address for any known router brand. It is a host address within the 192.168.100.0/24 subnet. The default gateway for this subnet — used by ARRIS, Motorola, Huawei, Zyxel, Ubee, and Ambit Microsystems devices — is 192.168.100.1. If your device has been assigned 192.168.100.21, it means your network's gateway is operating on the 192.168.100.x subnet and your device received this address via DHCP or static assignment.

Why does my device have the IP address 192.168.100.21?

Your device was assigned 192.168.100.21 by the DHCP server running on your gateway — most likely an ISP-provisioned modem-router from ARRIS, Motorola, Huawei, Zyxel, or Ubee. These devices automatically distribute IP addresses in the 192.168.100.x range to all connected clients. The address 192.168.100.21 simply means your device was the twenty-first host to request an address (or it was manually assigned this address as a static IP). Your gateway's admin panel remains at 192.168.100.1.

Can I use 192.168.100.21 to log in to my router?

Only if a device on your network has been specifically configured to use 192.168.100.21 as its management address. In the vast majority of cases, the admin login page for routers and gateways on the 192.168.100.x subnet is located at 192.168.100.1 — not at 192.168.100.21. If you are trying to access your ARRIS, Motorola, Huawei, Zyxel, or Ubee gateway's settings, navigate to 192.168.100.1 in your browser instead.

What is the default username and password for devices on the 192.168.100.x subnet?

Default credentials vary by manufacturer. For the most common brands associated with the 192.168.100.x subnet: ARRIS devices typically use admin / password or cusadmin / highspeed; Motorola devices use admin / motorola; Huawei devices use admin / admin; Zyxel and Ubee devices use credentials printed on the device label. Always check the sticker on the bottom or back of your gateway for the exact default login details, as ISPs sometimes customize these credentials before deployment.

How do I find my actual gateway address if 192.168.100.21 is not working?

On Windows, open the Command Prompt (Start > cmd) and type ipconfig, then press Enter. Look for the Default Gateway field — this is the address you should use to access your router's admin panel. On Mac or Linux, open Terminal and type ip route or netstat -nr. If your gateway is on the 192.168.100.x subnet, the Default Gateway will most likely show 192.168.100.1. You can also check our full guide to find your router IP address.

Can two devices share the IP address 192.168.100.21?

No. Within any single network, each IP address must be unique. If two devices are both assigned 192.168.100.21 — whether through a DHCP misconfiguration or conflicting static assignments — an IP address conflict will occur. This causes both devices to lose network connectivity intermittently or entirely. Your ARRIS, Motorola, Huawei, Zyxel, or Ubee gateway's DHCP server is designed to prevent this automatically, but conflicts can still arise if you manually assign static IPs without checking the DHCP lease table first.