Member Avatar for nyiaung

Hi,

I have Two Networks in connection as following,

First Network -------> switch --------> router -------> Second Network

First network's ip is 10.100.A.A , it's subnet mask is

Switch's ip is 10.100.B.B , it's subnet is also

router's ip is 10.100.C.C , it's subnet is also

Second network's ip is 10.10.D.D , it's subnet is also


The problem is as following

1. I can ping from First network to switch but cannot thence to router and also to second network
2. I can ping from switch to router but cannot thence to second network
3. I can ping from second network to router but cannot thence to switch and also first network
4. I can ping from router to both switch and first network

Medias are as follow:

Fibre optics between switch and router
ethernet between switch and first network
ethernet between router and second network

Please advice me for the above,
Thank in advance.

  • 2 Contributors
  • 1 Reply
  • 272 Views
  • 22 Hours Discussion Span
  • Latest Post Latest Post by hamidvosugh

Dani AI

Generated

A quick diagnosis tied to the symptoms reported by : the router can reach both sides but hosts cannot talk across it. That pattern usually means a layer‑2/3 mismatch or gateway/route problem rather than a bad fibre link. As noted, devices that share a physical LAN must share the same L3 subnet if they are expected to be on‑link; a switch management address in a different subnet will not act as a host gateway.

Useful, non‑disruptive checks (observe device consoles or logs rather than changing configs blindly): verify each host’s IP, netmask and default gateway; confirm the switch port to the router is in the same VLAN as the hosts (or that the trunk/subinterfaces are correct); inspect ARP tables and run traceroutes to see where packets stop; and on the router check that IP forwarding is enabled and there are no firewall/NAT rules blocking inter‑interface forwarding.

Example commands to gather facts quickly:

# Windows host
ipconfig /all
tracert <destination>

# Linux host
ip addr show
ip route show
traceroute -n <destination>

# Router / managed switch (Cisco-like)
show ip interface brief
show ip route
show running-config | include ip nat|ip access‑list

Corrective actions that resolve this class of problem: place the router’s LAN interface in the same /24 as the hosts and set hosts’ default gateway to that router IP; if the switch is a layer‑3 device, give it a default route pointing to the router (or let it route and add the router as next hop); ensure the switch port to router is the host VLAN (or a trunk with matching subinterfaces); enable routing/forwarding on the router (e.g., net.ipv4.ip_forward on Linux) and remove blocking firewall/NAT entries. Care should be taken when changing live addresses to avoid service disruption.

Member Avatar for hamidvosugh

I think the IP addressing scheme is wrong. You should have the first network and the switch(not required to have an IP address except for management purpose) and the interface of the router in same IP address range. Let's say 10.100.100.A with a mask of and apply same concept for the second network

Be a part of the DaniWeb community

We're a friendly, industry-focused community of developers, IT pros, digital marketers, and technology enthusiasts meeting, networking, learning, and sharing knowledge.