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We have a been problems with new Macbook Pro and Cisco Wireless. We able to see that some time the Macbook assuming the IP Address of network default gateway.

Looking for mac address of the default gateway, we see the Macbook MAC Address, not the MAC Address from network default gateway.

This problem occurs and is solved without any configuration.

Has anyone seen similar issues or know how to resolve it?

  • It’s very uncommon to not support Apple on a network these days, does your IT department review - cisco.com/c/dam/en/us/td/docs/wireless/controller/technotes/8-6/… – bmike Jul 25 at 0:42
  • Hi Bmike I am a Wireless Engineer of the network. I applied the Cisco Best Pratices, but its not the problem. The Macbook is assuming the gateway and answer the ping from gateway and from the address received by DHCP. Eg: My gateway as 192.168.200.1, the Macbook recive the addres 192.168.200.10. We are able to ping both Ip address, and the arp was the same mac address of Macbook. Regards Estéfano – Estéfano Mello de Aguiar Jul 25 at 18:58
  • Nice - so I'll add what the next step would be for me - the answer I make will likely be iterative, but at least you can confirm in comments that you ruled out the items. – bmike Jul 25 at 21:12
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Make sure your DHCP pool does not overlap with your default gateway. Thats the most common problem with what you are describing.

  • Hi Thomas The Macbook is assuming the gateway and answer the ping from gateway and from the address received by DHCP. Eg: My gateway as 192.168.200.1, the Macbook recive the addres 192.168.200.10. We are able to ping both Ip address, and the arp was the same mac address of Macbook. Regards Estéfano – Estéfano Mello de Aguiar Jul 25 at 18:58
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On the macOS end - you have unix heritage and tools, so let's look at how you pick apart which network interfaces have grabbed which addresses and match what the system was told in response to DHCP broadcast. You could enable packet capture / Wireshark if needed, but here are the quick tools I'd use:

ifconfig -uv
networksetup -listallhardwareports

Pay attention to the en0 / en5 / en whatever since those are ethernet and not tunnels or wireless discovery interfaces.

for me I have ethernet USB adapter (en4) and WiFi (en0)

ipconfig getpacket en0

So the likely values you want from the longer list are:

mac:~ me$ ipconfig getpacket en0 | grep -e addr -e server -e xid
xid = 0xc9d9ceb7
ciaddr = 192.168.1.27
yiaddr = 192.168.1.27
siaddr = 0.0.0.0
giaddr = 0.0.0.0
chaddr = a8:66:7f:4:d:1
server_identifier (ip): 192.168.1.1
domain_name_server (ip_mult): {192.168.1.1, 1.1.1.1}

At this point you'll know if another device is answering DHCP broadcasts or if the Mac has gotten an IP address it wasn't assigned and messing up your network thoroughly.

  • Hi B Mike Thanks for your attention. We will follow your steps and return. – Estéfano Mello de Aguiar Jul 25 at 22:15
  • I hope this is a decent start, it might be several steps or a slam dunk. Glad to be along for the journey. Great question @EstéfanoMellodeAguiar – bmike Jul 25 at 22:20

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