Local network devices cannot communicate with the routers at 195.105.1.1 and 195.105.1.2 because these IP addresses belong to a public Class C range, not your private local subnet of 165.18.0.0/10. The primary issue is likely an IP address conflict or misconfigured routing table where the router interface IPs do not match the expected gateway for the connected devices.
Understanding the Network Topology
The scenario involves two distinct network segments that are failing to interoperate correctly. You have an ISP-provided router operating at 195.105.1.1 and a secondary router at 195.105.1.2. Simultaneously, your end-user devices are configured within the 165.18.0.0/10 private address space. This creates a fundamental logical disconnect. A device on the 165.18.x.x subnet expects its default gateway to be an IP within that same subnet, typically something like 165.18.0.1 or 165.18.1.1. It does not know how to reach 195.105.1.1 without explicit static routes, which consumer-grade setups rarely handle automatically. Furthermore, 195.105.1.0/24 is a publicly routed block. If your ISP assigned these specific IPs to their gateway, they are external to your local LAN. If you intended these to be internal gateway addresses, you are using public IP ranges internally, which causes massive issues with NAT (Network Address Translation) and internet connectivity. Most home and small office networks use RFC 1918 private ranges such as 192.168.x.x, 10.x.x.x, or 172.16.x.x-172.31.x.x. Using 165.18.0.0/10 is technically valid as a private range in some contexts but is extremely large and unusual for typical home setups, suggesting a potential configuration error or a very specific enterprise requirement.The Gateway Mismatch
When a device attempts to send traffic to another device on the same local network, it checks its subnet mask. For a /10 mask, any IP starting with 165.18.*.* is considered "local." However, if the router's LAN interface is set to 195.105.1.1, the switch between them is bridging two different logical networks. Devices on the 165.18 side will try to ARP for the gateway MAC address. If the router is listening on 195.105.1.1, it will not respond to ARP requests for 165.18.x.x addresses unless specific proxy ARP settings are enabled, which is rare and often disabled by default for security reasons. This mismatch means that even if the physical cables are connected properly, Layer 2 communication fails because the devices are shouting on different logical channels. The router at 195.105.1.1 might be acting as a modem-only bridge, passing the public IP directly to your second router. In this case, the second router should be receiving a public IP via DHCP from the first, not having a static IP of 195.105.1.2 assigned manually on its WAN port while also trying to serve a different LAN subnet.Diagnosing the Connection Type
To resolve this, you must determine how the two routers are physically and logically connected. Are they connected via Ethernet cable between a LAN port on one and a WAN port on the other? Or are they connected LAN-to-LAN? The behavior changes drastically based on this choice. If connected WAN-to-WAN (Router 1 LAN to Router 2 WAN), Router 1 is providing internet access. Router 2 should obtain an IP from Router 1. If Router 1 is at 195.105.1.1, it likely hands out an IP in the 195.105.1.x range to Router 2's WAN interface. Router 2 then creates its own private network (e.g., 192.168.1.x) for its devices. Your devices are on 165.18.0.0/10. This implies Router 2's LAN is configured incorrectly or there is a third network segment involved. If connected LAN-to-LAN, both routers are part of the same broadcast domain. In this mode, you must disable the DHCP server on the second router to prevent IP conflicts. If both routers are handing out IPs, devices will receive conflicting gateway instructions. One device might get 165.18.0.2 with gateway 195.105.1.1, while another gets 165.18.0.3 with gateway 195.105.1.2. Since neither gateway exists on the 165.18 subnet, no device can route traffic effectively.Step-by-Step Resolution
You need to align the IP addressing scheme so that all devices and gateways exist within the same logical subnet or have proper routing between them.- Check Physical Connections: Ensure the cable connects the LAN ports of both routers if you want a single flat network, or LAN to WAN if you want double NAT (isolated subnets).
- Verify Subnet Consistency: Log into the admin panel of both routers. Check the LAN IP settings. If your devices are on 165.18.0.0/10, both routers' LAN interfaces must have IPs within this range (e.g., 165.18.0.1 and 165.18.0.2). Change the router IPs if they are currently 195.105.1.x.
- Disable DHCP on Secondary Router: If using LAN-to-LAN connection, log into the second router (195.105.1.2) and turn off its DHCP server. Let the primary router (195.105.1.1) handle all IP assignments. Assign a static IP to the second router within the 165.18.0.0/10 range but outside the DHCP pool.
- Update Default Gateways: On your client devices, ensure the default gateway is set to the correct router IP (e.g., 165.18.0.1). If using automatic configuration, ensure the DHCP server is pointing to the correct gateway.
Common Pitfalls and Advanced Fixes
Sometimes the issue is not just IP addresses but firewall rules. Some ISPs lock down their provided routers, preventing LAN-to-LAN communication or blocking certain ports. If you are using the ISP router strictly as a modem, ensure it is in Bridge Mode. This disables its routing functions and allows your second router to handle all NAT and DHCP duties. Another possibility is VLAN tagging. If your network infrastructure supports VLANs, the two routers might be on different VLANs. Without a Layer 3 switch or router capable of routing between these VLANs, devices cannot communicate. Check if your switches have VLAN configurations that separate the 195.105.1.x traffic from the 165.18.0.x traffic. If you are attempting to bypass ISP restrictions, note that modifying router firmware or settings may violate your service agreement. See Circumventing T-Mobile Wireless Modem Restrictions for context on why some ISPs restrict direct router connections, though this specific guide focuses on wireless modems, the principle of ISP lock-down applies broadly. Ensure that your subnet mask is correctly set to 255.255.0.0 (or /16) or appropriate for /10 (255.192.0.0) on all devices. A mismatched subnet mask can make devices believe they are on different networks when they are physically connected to the same switch.Frequently Asked Questions
Can I use public IP addresses on my local network?
No, using public IP ranges like 195.105.1.x internally will cause severe routing conflicts and internet connectivity failures. You should always use private RFC 1918 addresses for local LAN segments to avoid overlapping with global internet routes.
Why do my devices work on Wi-Fi but not Ethernet?
This usually indicates that the Wi-Fi SSID is associated with a different VLAN or subnet than the wired ports. Check your switch and router configurations to ensure both wireless and wired interfaces are bridged to the same logical network segment.
What is the difference between LAN-to-LAN and LAN-to-WAN connections?
LAN-to-LAN creates a single network segment where one router handles DHCP, while LAN-to-WAN creates two separate networks with double NAT. LAN-to-LAN is better for device discovery, while LAN-to-WAN provides isolation but breaks local communication between subnets.
How do I find the correct gateway IP for my devices?
On Windows, open Command Prompt and run ipconfig. On macOS/Linux, use ifconfig or ip route. Look for the "Default Gateway" entry. This IP must match the LAN IP address of the router serving your subnet.
Is Proxy ARP required for mixed subnets?
Proxy ARP allows a router to answer ARP requests for IPs it doesn't directly own, but it is generally discouraged due to security risks and performance overhead. It is better to fix the subnet configuration rather than relying on Proxy ARP.