Can`t see DHCP offer packet in Wireshark sent with sendp from scapy

i try to implement an DHCP Server in scapy. I sniff with iface="Local Area Connection 3" for udp sport 67 and dport 68 for DHCP Discovers and then sending DHCP Offer with sendp command. I can't see in Wireshark my packet, and DHCP Clinet don`t receive either, it contiunes to send DHCP Discovers.On wireshark i only see DHCP Discovers from client. Here is the code:def sniff_DHCP_discovers(): sniff(filter='port 67 or port 68', prn=startThread, iface="Local Area Connection 3")def startThread(pkt): thread = threading.Thread(target=process_DHCP...Read more

dhcp - how to send ascii value as option 43 (VCI) in dnsmasq?

I want to send a number as a string in DHCP Ack for vendor class matching say="Prash" , how do i send effectively?Im using dnsmasq and i tried putting an option in dnsmasq.conf file as followingdhcp-option=vendor:Prash,1,403This will match for all vendor class matching "Prash" and adds option 43 VCI in dhcp ack with 403.In wireshark im however getting a random value, Can anyone suggest how exactly to send ASCII value as "403"?Wireshark :...Read more

DHCP: stuck between DHCP offer and DHCP request

Here is an image of my current topology (this is a real topology, just added the packet tracer image so you can picture it):topology when the client on the right sends the DHCP DISCOVER (broadcast), the router redirects it to the DHCP server with the IP of the gateway as source and IP of the DHCP server as destination (unicast). The DHCP server then replies DHCP OFFER with its IP address as source and the fa0/1 IP address as destination (unicast).However, this does not reach the client, and it does not...Read more

rfc - DHCP Options field padding

According to RFC2132 "Pad Option" (0s) CAN be used to align subsequent fields on word boundaries. But looking at DHCP packets I can't tell what is the size of the "word". Onetime "Options" field is 32 bytes, one time is 60 bytes.In my setup the DHCP server has no problem accepting packets with no padding.Is padding required anymore nowadays? If it is to what size?...Read more

dhcp - busybox udhcpc received NAK

I have a custom board with LPC1788, 32Mbyte SDRAM, 128 Mbyte Nand flash, on 108Mhz.I download the emcraft uclinux and networking project.The poroblem is the busybox udhcpc command:init started: BusyBox v1.17.0 (2014-12-05 16:25:33 CET) ~ # ifconfig ~ # udhcpc -f -i eth0 udhcpc (v1.17.0) started Setting IP address on eth0 Sending discover 0... Sending discover 0... Sending select for Received DHCP NAK Sending discover 0... Sending select for Received DHCP NAK Sending discover 0... Sending select for 192.16...Read more

How can a DHCP OFFER message be unicast?

Why is a DHCP OFFER message is destined to IP: (which was assigned to my PC by DHCP server later) before even the system configured it? When the host is still asking for an IP address, how can server send a unicast message. The host's IP address will still be So, can anyone explain this?...Read more

Does DHCP client receive DHCP NAK if any of the parameters are wrong in DHCP Release?

I am building a dhcp client using C on Ubuntu 9.04. Now I send a dhcp release to the dhcp server, it sends no ack as expected. I was wondering if it sends any DHCP NAK if any of the parameters are wrong.There is one more problem. After sending DHCP Release my internet is still working. Also when I do ifconfig it still shows the ip address of eth0.But when I do dhclient -r internet does not work and ifconfig does not show the ip address of eth0....Read more

Why are DHCP Offer and Ack broadcasted?

Why can't the server use the destination IP address of as is used in source IP of DHCP Discover and Request? It can use the MAC address of the client learnt from DHCP Discover and Request to direct the frame to the appropriate client machine....Read more

what is boot image in the DHCP

I read in the e.comer book that in dhcp the dhcp allow a computee to negotiate to find a boot image and to do so the host fills in field boot file name with the request and dhcp server does not send an imageI realy can not understand a single wordNeed help...Read more

dhcp - BIND9 Dynamic Update not working - NOTZONE and SERVFAIL errors

This is on CentOS 7 with BIND9. When I run nsupdate to test ddns updating, I get a couple levels of failure. On adding the reverse zone, I get . Then on adding the forward zone entry, I get . I've reached the end of google in trying to identify what I'm doing wrong - does anyone see what's the problem here? I'm not even getting into DHCPD yet, though I have it all configured and ready to go. nsupdate> server> key rndc-key xxxxxxxxxxxxxxxxxxxxxxx==> zone> update add more

static ip address - How to configure access points and dhcp ranges?

I have a Thomson ST585V6 router and 2 TRENDnet TEW-636APB Wireless Access Points. And I have 3 devices that need a static IP address. All the other devices need to have their IP adreess assigned with DHCP. Here is what I did:In each of the 3 devices that need static IP I assigned the static IPs, and Then I assigned statics IPs to the two access points and I also made this access points DHCP Servers with DHCP pool addresses - (one of them) more

dhcp - Unable to execute configuration on router through TFTP's python script

I am trying to use the ZTP approach to configure my router [R2]. My Ubuntu machine is both DHCP and TFTP server. Ubuntu [DHCP Server]: 16.04.5 LTSCisco Router [DHCP Client]: 7200, version 15.2(4)S5This is the python script- is stored in /var/lib/tftpboot/#!/usr/bin/env python3.5.2import timeimport clitime.sleep(200)print ("\n\n *** ZTP Day 0 Configuation *** \n\n")fn = open('TXJla-outgoing/R1.txt','r') =fn.readlines()fn.close()cli.configurep([c])The configuration on dhcpd.conf for host R2 is -host R2 { hardware ether...Read more

DHCP of LXC on Proxmox doens't work

I give up, for days I have trying to figure it out. So any help will be very welcome.I have a Proxmox virtualization server and everything works fine, except that none LXC (Linux Container) can get an answer from the DHCP server.I have the following:LXC + DHCP client = No LXC + static IP = YesVM + DHCP client = YesVM + static IP = YesTherefore I know it isn't a firewall or networking issue.My best guess it is a kernel issue, but again I have another Proxmox server on the same network (and same Proxmox cluster) that works fine....Read more

arp - How are DHCP Replies unicasted by DHCP Server or DHCP Relay Agent?

While DHCP Request messages are allways sent via broadcast during DHCP Client initialization phase, DHCP Replies can be sent as both broadcast and unicast. Which method of sending will be used depends on the DHCP Server or DHCP Relay Agent and requirement of a DHCP Client.DHCP Client can request that DHCP Replies are broadcasted in case that it's own IP protocol implementation software can not receive unicast IP packets untill it has valid IP address configured and that is the case in the initialization phase. In this case it will specifically ...Read more

Why are DHCP request and acknowledgment messages broadcasted and not unicasted?

In 'Request' part of the DORA process, IP and MAC address of the DHCP server is known to the client (as the IP datagram sent in Offer has this information). So if the destination is known, why is the request still broadcasted to every machine on the network?Similarly in 'Ack' part of the DORA process, the IP address of the client is now successfully set inside it and known to the DHCP server. Why does it still broadcast the message?...Read more