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LeRouteur
Asked: 2021-12-06 06:59:22 +0800 CST

Cannot ping GW using static IP in a specific subnet, but can ping it using another subnet

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I just ran against a strange problem a few weeks ago, and I'm still scraching my head about it.

We have an auth server (WServ 2016) running ADDS/ADFS/DNS/DHCP, having 172.17.0.5/24 as static IP and GW set to 172.17.0.1. The 172.17.0.5/24 subnet is dedicated to common services used by each subnet.

There are other subnets, such as 172.17.1.0/24 (managed services), 172.17.127.0/24 (storage ressources) and 172.17.128.0/20 (hosting ressources).

A pfSense router/FW makes the job for inter-subnet communication and Internet access (there are virtual IPs on the LAN NIC).

I had to reboot the auth server a few hours ago, and it won't go back online. I cannot ping the GW using the 172.17.0.5/24 IP, or using any IP in the 172.17.0.0/24 subnet. But if I set the static IP to 172.17.1.19/24 i.e., I can ping everything and access the Internet.

There is no FW rule blocking the communication between subnets, since this a pre-prod network.

I suspected an equipment already using the 172.17.0.5 IP, but since the whole subnet appears to be blocked, I don't know what to check.

Any idea about this?

networking

1 Answers

  1. I cannot ping the GW using the 172.17.0.5/24 IP, or using any IP in the 172.17.0.0/24 subnet. But if I set the static IP to 172.17.1.19/24 i.e., I can ping everything and access the Internet.

    Apparently, that server has moved to a different VLAN (assuming your subnets are separated into VLANs). Check switch configs and cabling.

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