As a WISP operator it can be difficult to track an IP Address directly back to a customer if DHCP is being used. This is especially true if the operator is attempting to track activity that occurred at some point in the past where the IP Address is no longer associated to the same customer. Typically the only information in the DHCP Server logs associated with the IP Address is the MAC Address of the customer’s router (which can easily disappear from the network if the customer changes their router or cancels service.)
A feature which can be enabled on PMP450 called Option 82 can help with this though.
Option 82 is a protocol extension for Relay Agents. Relay Agents are devices on the network that will forward a DHCP request to other subnets on a network (usually traversing routers). As these Relay Agents forward the DHCP request they have the ability (via Option 82) to tag on additional information about the request. Specifically they can define a field called “Circuit ID” and a field called “Remote ID”. For PMP450 when “Option 82” is enabled the AP will populate the Circuit ID of the DHCP Request with its own MAC Address and populate the Remote ID with the MAC Address of the SM where the request originated. So now the log of the DHCP Request will show 3 MAC Addresses. First, it will show the MAC Address of the device requesting an IP Address (typically a customer router). Second, it will show the MAC Address of the AP. Third, it will show the MAC Address of the SM through which the customer is connected.
Configuring Option 82:
To configure Option 82 for PMP450, Select “Tools->General”. Scroll down to “DHCP Relay Agent” and select “Enable – Only Insert Option 82”. Save and Reboot.
DHCP Lease Examples:
Before Enabling Option 82:
lease 192.168.10.124 {
starts 3 2014/09/10 18:22:02;
ends 3 2014/09/10 18:32:02;
cltt 3 2014/09/10 18:22:02;
binding state active;
next binding state free;
rewind binding state free;
hardware ethernet 00:17:fa:37:e7:e5; <-MAC Address of customer router
uid "\001\000\027\3727\347\345";
}
After Enabling Option 82:
lease 192.168.10.124 {
starts 3 2014/09/10 19:04:11;
ends 3 2014/09/10 19:14:11;
cltt 3 2014/09/10 19:04:11;
binding state active;
next binding state free;
rewind binding state free;
hardware ethernet 00:17:fa:37:e7:e5;
uid "\001\000\027\3727\347\345";
option agent.circuit-id a:0:3e:a1:2f:43; <- MAC Address of AP
option agent.remote-id a:0:3e:a0:5:16; <- MAC Address of SM
option agent.unknown-9 0:0:0:a1:6:13:4:1:2:0:0; <- MAC Address of customer router
}
AP MAC Address
SM MAC Address
