Netgate Discussion Forum
    • Categories
    • Recent
    • Tags
    • Popular
    • Users
    • Search
    • Register
    • Login

    DHCP requests with option 50 after adding a static mapping for the device.

    Scheduled Pinned Locked Moved DHCP and DNS
    1 Posts 1 Posters 1.6k Views
    Loading More Posts
    • Oldest to Newest
    • Newest to Oldest
    • Most Votes
    Reply
    • Reply as topic
    Log in to reply
    This topic has been deleted. Only users with topic management privileges can see it.
    • R
      ryan87
      last edited by

      Hi,

      I've been running into this for a while now and I don't think the behavior is correct.  I've only tested on Windows machines.  I do the following:

      • Connect a device that uses DHCP and get an IP address

      • Find the MAC address and add a static DHCP mapping

      • Run ipconfig /release followed by ipconfig /renew

      I always end up getting the old, non-static DHCP IP.  For example, I tested on a Windows 10 VM with pfSense 2.3.2-RELEASE-p1 (amd64).  After a fresh Windows 10 install, I was assigned the IP address 192.168.100.220.  I logged in to pfSense and added a static DHCP mapping for the device.  Then I release the IP:

      11:40:55.633455 IP (tos 0x0, ttl 128, id 22267, offset 0, flags [none], proto UDP (17), length 328)
          192.168.100.220.68 > 192.168.100.254.67: [udp sum ok] BOOTP/DHCP, Request from 08:00:27:48:ce:81, length 300, xid 0xed9ed100, Flags [none] (0x0000)
                Client-IP 192.168.100.220
                Client-Ethernet-Address 08:00:27:48:ce:81
                Vendor-rfc1048 Extensions
                  Magic Cookie 0x63825363
                  DHCP-Message Option 53, length 1: Release
                  Server-ID Option 54, length 4: 192.168.100.254
                  Client-ID Option 61, length 7: ether 08:00:27:48:ce:81
                  END Option 255, length 0
                  PAD Option 0, length 0, occurs 41
      

      Next I renew the IP.  The request:

      11:40:59.048937 IP (tos 0x0, ttl 128, id 15824, offset 0, flags [none], proto UDP (17), length 351)
          0.0.0.0.68 > 255.255.255.255.67: [udp sum ok] BOOTP/DHCP, Request from 08:00:27:48:ce:81, length 323, xid 0x52abb8af, Flags [none] (0x0000)
                Client-Ethernet-Address 08:00:27:48:ce:81
                Vendor-rfc1048 Extensions
                  Magic Cookie 0x63825363
                  DHCP-Message Option 53, length 1: Request
                  Client-ID Option 61, length 7: ether 08:00:27:48:ce:81
                  Requested-IP Option 50, length 4: 192.168.100.220
                  Server-ID Option 54, length 4: 192.168.100.254
                  Hostname Option 12, length 13: "netman-portal"
                  FQDN Option 81, length 16: "netman-portal"
                  Vendor-Class Option 60, length 8: "MSFT 5.0"
                  Parameter-Request Option 55, length 13:
                    Subnet-Mask, Default-Gateway, Domain-Name-Server, Domain-Name
                    Router-Discovery, Static-Route, Vendor-Option, Netbios-Name-Server
                    Netbios-Node, Netbios-Scope, Classless-Static-Route, Classless-Static-Route-Microsoft
                    Option 252
                  END Option 255, length 0
      

      …and the reply:

      11:40:59.049733 IP (tos 0x10, ttl 128, id 0, offset 0, flags [none], proto UDP (17), length 328)
          192.168.100.254.67 > 192.168.100.220.68: [udp sum ok] BOOTP/DHCP, Reply, length 300, xid 0x52abb8af, Flags [none] (0x0000)
                Your-IP 192.168.100.220
                Client-Ethernet-Address 08:00:27:48:ce:81
                Vendor-rfc1048 Extensions
                  Magic Cookie 0x63825363
                  DHCP-Message Option 53, length 1: ACK
                  Server-ID Option 54, length 4: 192.168.100.254
                  Lease-Time Option 51, length 4: 7200
                  Subnet-Mask Option 1, length 4: 255.255.255.0
                  Default-Gateway Option 3, length 4: 192.168.100.254
                  Domain-Name-Server Option 6, length 4: 192.168.100.254
                  Domain-Name Option 15, length 17: "...[domain removed]..."
                  END Option 255, length 0
                  PAD Option 0, length 0, occurs 7
      

      Why does the DHCP honor the Option 50 request?  Shouldn't it ignore the request and assign the IP I've allocated via the static mapping?

      1 Reply Last reply Reply Quote 0
      • First post
        Last post
      Copyright 2025 Rubicon Communications LLC (Netgate). All rights reserved.