Questions tagged [dhcp-option]

The Dynamic Host Configuration Protocol (DHCP) provides a framework for passing configuration information to hosts on a TCP/IP network. Configuration parameters and other control information are carried in tagged data items that are stored in the 'options' field of the DHCP message. The data items themselves are also called "options".

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How to send custom DHCP option on all Offer and Ack packets in kea?

I'm using the Kea dhcp server, and I want to use the DHCP options to send data to the server's clients. Following the instructions here, I listed the option with the "always-send": true ...
0 votes
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545 views

Implementing rfc3442 (classless static route) in Freeradius DHCP server

I am trying to setup a Strongswan server that runs in split tunnel mode, which means I have to disable using the server as a default gateway on client side and also disable classfull routing in the ...
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Using DHCP reservations instead of static IP address configuration for servers

I was wondering if it is better to use DHCP reservations for servers and computers that must have static IP address, excluding DHCP servers themselves, Domain Controllers, and DNS servers of course, ...
1 vote
1 answer
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DHCP: When (which step of DORA) do options get sent?

Everyone knows that there are 4 steps to a DHCP handshake. Everyone talks about DORA (Discover, Offer, Request, Ack) and the "happy path" to getting an address, and this is the most common ...
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How can I implement single letter domains for LAN internet browsing using dnsmasq?

In our LAN I have several services running in multiple hosts, and clients using DHCP with dnsmasq. My goal is that any user can type a single letter (e.g. c) in the browser search bar and get in ...
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How i can assign /32 ip address to openstack nova instance without float ip?

I'm developing a custom panel for my openstack home lab via rest api. I've investigated Hetzner cloud ip (v4) addressing mechanism and i found it is like this: It is assigning /32 valid ip v4 address ...
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1 answer
196 views

isc dhcp multiple option 240 in same subnet

I'm fairly new to isc dhcp. I'm working at an ISP and need to provide our STB's with an option 240, and it has worked fine for years, the problem now is that we are getting a newer model, that needs a ...
0 votes
1 answer
382 views

DHCP Pools on Ubuntu DHCP server not working properly

Mac addresses ending with "55:a3" and "56:2a" are also ending up in last pool 123 match if binary-to-ascii(16,8,":",substring(hardware, 5, 6)) = "55:a3"; ...
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1 answer
570 views

Define multiple filename options in DHCP config based on different range

Intro I am trying to use a centos box for DHCP and TFTP function, for iPXE boot. I have one subnet configured for DHCP, but it has multiple ranges and each range has a different iPXE boot URL. Problem ...
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How to get custom option on client from ISC DHCP server

Over ISC-DHCP server I wanted to define a custom DHCP Option, for which I am using below config option imagefile code 224 = ip-address; subnet 192.168.29.0 netmask 255.255.255.0 { range 192.168.29.1 ...
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How to include vendor-specific option 17 suboptions 11, 12 and 13 in DHCPv6 solicit/request using dhclient

My request is to include option 17 sub-options 11, 12 and 13 in DHCPv6 solicit/request and I configured the same in dhclient6.conf on my Ubuntu as below. send dhcp6.vendor-opts 00:00:0d:e9:00:0b:00:06:...
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How does MS DHCP server decide which DNS server to try to dynamically update?

In MS DHCP, under Scope Properties, on the DNS tab, it says: You can setup the DHCP server to automatically update authoritative DNS servers with the host (A) and pointer (PTR) records of DHCP ...
1 vote
2 answers
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Alpine Linux is not sending hostname to dhcp server

When alpine linux asks for ipv4 address from dhcp server, it is not sending hostname to dhcp server. So I cant access by server's hostname in LAN. Here is my setup I am using Alpine Linux 3.12 on my ...
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2 votes
1 answer
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What happens when specifying multiple dns servers with DHCP Option 6?

If I have the following DHCP option 6 (DNS), what happens? 6,1.1.1.1,8.8.8.8 Will 1.1.1.1 be served, and 8.8.8.8 as fallback if 1.1.1.1 fails? Extra context: I am running odhcpd on OpenWRT with pi-...
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3 answers
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Why can't I use IPv6 address for DHCPv4 client option 6 (DNS server)

I am trying to configure options for a DHCP network and the proprietary software (that is layered on top of ISC's DHCP server) that I am using won't allow me to put in an IPv6 address. In other ...
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3 votes
1 answer
492 views

DHCP Option in HSRP /VRRP

I'm configuring HSRP having scenario described in figure below. One gateway is active for one network and standby for other network and vice versa for other gateway. DHCP is configured on both ...
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1 answer
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dhclient.conf - append to system hostname [duplicate]

I'm running a Raspbian on a bunch of Raspberry Pis. They each have a unique hostname set in /etc/hostname and the dhcp client correctly registers that name with my router. The problem I'm running ...
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How many DHCP Pad Option Bytes should be added?

RFC 1553 (DHCP Options) states: 3.2. End Option The end option marks the end of valid information in the vendor field. Subsequent octets should be filled with pad options. The code for the ...
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How to add more than 32 routes to isc-dhcp-server and separate them to 2 fields?

Is there any way to add long list routes to server? Actually now I can add only 32 routes because we have only 1 octet for them. After adding more than 32 routes I received "Malformed packet" by ...
-1 votes
1 answer
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DHCP: Advertise DNS Server with port (not 53)

In my network I have a small docker swarm running several apps. Latest I tried to setup two new services offering DHCP with ispcpd and DNS with unbound to the network. Master of the swarm is a new ...
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1 answer
459 views

DHCP snooping - my clients dont get ip from dhcp

Why the PCs don't get ip from Core switch Dhcp pool? without dhcp snopping there is no problem, but when i enable dhcp snooping clients stoping to get ip from dhcp. This is my topology: topology ...
1 vote
2 answers
555 views

dhcrelay append option 66 and 67

I'm running a PXE Linux server in a VLAN. How is it possible to use [dhcrelay][1] to forward the DHCP requests to the main DHCP server and add the options for PXE with dhcrelay? I've tried something ...
0 votes
1 answer
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How can I configure DHCP server to issue the same fixed-address by matching with the client identifier in the discover message

I am able to config fixed ip address with hardware ethernet options, but i am trying to assign fixed ip based on client id(option 61) from DISCOVER message. I tried with below configs , but it doesn't ...
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1 answer
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Option 81 in DHCP

Just curious about this. When we enable option 81 on a DHCP network, the DHCP server will start updating the zone that comes along with the client's FQDN. Now, how would client will ever know its ...
2 votes
1 answer
4k views

DNSMASQ Specify Port Number in dhcp-option=6

I run Ubuntu 16.04 LTS. I want to redirect DNS requests coming from some ip[-range] to another instance of dnsmasq on port 1995. To do so I added these lines in /etc/dnsmasq.conf file : dhcp-range=...
1 vote
2 answers
8k views

Assigning a hostname of the fqdn assigned to a dhcp client with dnsmasq?

I'm aware that you can assign static DNS entry names by doing the following in dnsmasq.conf: address=/wiki.leerdomain.lan/192.168.1.200 ptr-record=wiki.leerdomain.lan/192.168.1.200 and then ...
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dhcpd daemon taking huge amount of memory and restarting with out of memory error

I have to configure isc-dhcp-server for 1 million clients which listens on 4094 vlan tagged interfaces, where each vlan interface is mapped to a subnet declaration. Therefore in total 4094 subnet ...
3 votes
2 answers
67 views

Server 2012R2 DHCP & DNS Updates

I have the following DNS settings configured on an DHCP scope: My question is, will the DNS entry be made against the DNS server that the DHCP is configured to go against or will it update the DNS ...
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-2 votes
2 answers
751 views

How do I configure Dynamic Host Configuration Protocol to return a FTP server's IP address along with the interface IP address?

Given that there is a dhcp client, a relay agent and dhcp server. There is also another ftp server. Requirement is that the client starts the DORA process and the server responds with IP address and ...
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1 vote
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OpenVPN: automatic proxy detection after connection is established

I have setup an OpenVPN server and an HTTP proxy server on the same host in cloud. I have also configured OpenVPN client on my desktop. I have also setup redirection rules on the cloud host to ...
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4 votes
1 answer
454 views

rfc 6939 support for dhcpv6 relay

isc-dhcp-server now supports rfc6939 as of version 4.3, and I would like to be able use it as it is quite nice to be able to just use the mac address to identify dhcpv6 clients. However, I can't seem ...
1 vote
1 answer
2k views

dhcpd option 82 logging not working

We are implementing Option 82 in our network and I am just scratching the surface of how to setup my server. I have successfully created my first Option 82 ACL based on the agent circuit ID that is ...
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4 votes
1 answer
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How to disable NetBIOS over TCP/IP on pfSense via DHCP

I have a pfSense applicance running version 2.x. I want to disable NetBios over TCP/IP via the DHCP Server so it is not activated on Windows clients. It's possible to do it with a Windows server but I ...
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DHCP server assigning same IP address even if Computer is connected in different VLAN

DHCP Server OS - Windows Server Standard 2008 R2 DHCP Client OS - Windows 7, Linux based OS etc.. I have configured DHCP Server on Windows Server Standard 2008 R2 with SuperScope. Let assume that i ...
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4 votes
1 answer
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Does a Windows host correctly interpret dnsmasq parameters?

I have a network of Windows 10 machines served (DNS and DHCP) by a dnsmasq instance on a Ubuntu server (Ubuntu 15.10, dnsmasq 2.75). The setup basically works (dnsmasq provides addresses and manages ...
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0 votes
1 answer
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classes declaration inside of subnets in isc dhcp

I would like to use class declarations based on a subnet scope, is that allowed? Or are all classes global scope? here is my dhcp.conf snippet: subnet 10.200.147.0 netmask 255.255.255.224 { ...
0 votes
1 answer
509 views

Is `127.0.0.1` a special token for Ubuntu 14 LTS `resolvconf` when DHCP pushes DNS settings?

Dear Linux Graybeards, Is 127.0.0.1 a magic token for resolvconf in Ubuntu 14 LTS when using DNS settings pushed by DHCP? I'm using Ubuntu 14.0.3 (LTS) in AWS (ami-0f8bce65) with custom DNS settings ...
2 votes
1 answer
382 views

Is it possible to set a dhcp option 77 value in vsphere as a config parameter so vNIC ROM (e1000/vmxnet3) uses it during PXE?

I'd like to set a dhcp option 77 string value in vsphere as a config parameter on a vm or vm template so that the vNIC ROM (e1000/vmxnet3) uses it during the DHCP part of PXE. My goal is to have PXE ...
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3 votes
1 answer
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How did AirPort's DHCP "Welcome Message" work?

I remember that Apple's AirPort base stations used to have a DHCP "Welcome Message" feature, that would display a custom pop-up dialog when computers connected to the network. How was this ...
4 votes
0 answers
2k views

VLAN ID over DHCP for Management Interface of Fortinet FortiAP

When configuring the FortiAP device it's desirable to configure the VLAN ID for the tagged management network. Accordingly to the manual it's possible to do so by "telnetting" to the FortiAP device ...
3 votes
0 answers
538 views

Can ISC-DHCP bind to Option 82 rather than Mac Addresses?

We use option 82 information to limit leases presently in ISC-DHCP using a spawn with statement for our billing subclass. This keeps a single household/business from obtaining more leases than they ...
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How can a dhcp client in linux can send the dhcp option 60 - specifying the vendor-id?

I am using fedora core machine. My linux- fedora core machine - client wants to send the dhcp option 60 specifying the vendor id to the dhcp server. Next, I want to read the dhcp option 43 send by the ...
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Cant deploy images with WDS: PXE-E16: No offer received

I am currently playing around with a WDS lab environment on a virtual 2012 R2 server, which is patched to the latest available update-level. This server is running the DHCP server role and has two ...
1 vote
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Sonicwall L2TP Server is using a "phantom" internal DHCP server

Following a few articles on options 121 and 249, I'd like to push out routes to the L2TP VPN clients using the internal DHCP server on the Sonicwall. However, the Sonicwall seems to be using a ...
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2 votes
2 answers
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ISC dhcpd dynamic bootfile-name. Is this possible?

Actually I want to dinamically assign bootfile-name based on clients MAC. I have tried this config: option bootfile-name concat( binary-to-ascii(16, 8, "", substring (hardware, 1, 6)), ".cfg"); But ...
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0 votes
1 answer
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How to trigger DHCP request and inspect the reply from DHCP server

Is it possible to trigger a DHCP request from my DHCP server and then sniff and inspect the whole DHCP reply from the server to see what options/parameters it sends to the clients?
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4 votes
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Assigning option based on class membership inside the subnet section

We are looking for a way to do something along these lines in the dhcpd.conf file: subnet ... { #couple of options for the subnet here pool { allow members of "class-name1"; ...
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1 vote
1 answer
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Libvirt providing bootp options without being configured to do so

I have a virtual network configured in libvirt and configured to provide DHCP (via dnsmasq) but not configured to provide bootp information (see below), but when I boot an iPXE ISO and look at the ...
1 vote
0 answers
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How to send several instances of the vendor-specific options to a DHCP server using dhclient?

I need to send vendor-options to DHCP server using dhclient (ISC). I've added following lines in the dhclient.conf: option dhcp6.vendor-class code 16 = {integer 32, integer 16, string}; send dhcp6....
2 votes
1 answer
3k views

Why use FQDN as DNS-server option in DHCP?

I've seen multiple default configurations of DHCP-servers with a FQDN set as the DNS-server option. Doesn't this imply a catch-22, or the need for that DNS-server to be in the hosts file of every ...