In DHCP, UDP port number 67 is used by a DHCP server, and UDP port number 68 is used by DHCP clients. The method to capture DHCP traffic is to define a filter so that tcpdump dumps only DHCP related traffic.
Basically, the tcpdump command can be used to do some packet sniffing on the network. This is very useful in cases where DHCP issues may have to be investigated. The tcpdump command can be used to monitor DHCP related network traffic. This will tell what was received from the DHCP server.Topics: Networking Using tcpdump to monitor DHCP network traffic You will see client MAC address, Your (client) IP address, gateway IP address as Router (Option 3), and subnet mask as Option 1. View the packet details (in Wireshark this is accomplished by going to View -> Packet Details. Highlight either a DHCP Offer packet or a DHCP ACK packet. This will only show DHCP packets out of the entire packet capture.ĥ. Within the packet capture use "bootp" as the filter. Once the device receives an IP, stop the packet capture.Ĥ. Restart the WiFi service on the smartphone or whatever client you are testing.ģ. Note that, the tool or the AP should be on the same channel as the network you are analyzing.Ģ. You can use Ruckus APs if you don't have a 3rd party tool. Start a wireless packet capture using your favorite tool.
This is an important detail because a wrong gateway can cause Internet access to fail. QuestionHow do I find out the gateway IP by looking at the DHCP packets? Customer EnvironmentWiFi network Root CauseNot all smartphones show IP address of the gateway when you go to WiFi setting. This method involves taking a packet capture and expanding DHCP options in the corresponding packets. This article explains one of the methods to find subnet mask and gateway IP if you would like to know what was received. SummarySome of the smartphones will only show received IP address under WiFi settings.
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