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Dell Server, broadcom NIC, 5 IP addresses all on the same subnet. Let's say 100.100.63.67-71. Windows Server 2003.

From another system on the 100.100.63.* subnet, I can ping all IP addresses no problem.

From a system on another subnet, say 100.100.58.*, I can ping all but one, the 100.100.63.70 address. It's in the middle of the IP range.

In Win2003 server, I specify the default gateway once as 100.100.63.1. Each individual IP has a subnet mask of 255.255.255.0. I've verified they are all the same.

I'm stumped... why would 100.100.63.70 not respond to pings from outside it's subnet, while the others will?

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Have you verified whether it is actually receiving the ICMP ping request by running tcpdump/wireshark or some other packet analyzer? –  TiCL Nov 15 '11 at 15:40
    
Have you tried ping 70 from the same network? You must decrease "point of failures" to identify (possible) single point –  Lazy Badger Nov 15 '11 at 20:40

3 Answers 3

You don't say what's separating the networks (firewall or router), but these would be the steps I'd take:-

  • If the device between the subnets is a firewall, make sure that it's configured to allow traffic for the .70 IP.
  • If firewall rules aren't the problem (or if the device is a router), check the ARP table. Try pinging the .70 IP from the firewall/router.
  • Using Wireshark (or similar) on the server, check to see if your ICMP packets are being received at all.

You don't say, but I'm assuming that you've tried from multiple devices on other subnets?

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I think this is the most likely possibility. Whatever router connects the two subnets likely has some leftover configuration that blocks either the ping or the reply. –  David Schwartz Nov 15 '11 at 17:07

It turns out that the router had a static mac address applied to that IP address, which was not the mac address of the NIC. Clearing the static entry immediately resolved the problem.

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5 IP addresses all on the same subnet. Let's say 100.100.63.67-71

Let's say - network 100.100.63.67-100.100.63.71 can not exist at all.

$ ipcalc 100.100.63.67-100.100.63.71
deaggregate 100.100.63.67 - 100.100.63.71
100.100.63.67/32
100.100.63.68/30

Write real data in order to get real answers!

Tracert from-to .70, ipconfig also welcomed. TiCL also totally correct - verify, that your get ICMP, you answer on ICMP, you have correct route table (you must anwser from the same interface, which received packet)

Edit: Before checking logical conditions (network settings), you have to check physical also before - cable, NIC-port, switch port

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He specifically states they're 5 IPs within a /24 when he says they have a mask of 255.255.255.0. –  Andy Smith Nov 15 '11 at 16:11

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