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I've decided to try to request an IP using scapy. I am able to send out a discover and receive an offer in the variable ansD. Unfortunately I'm having trouble accessing the field that contains the offered IP address which should be ansD[BOOTP].yiaddr . It tells me that the field does not exist. I have looked around and have seen similar issues but cannot seem to understand why I can access normal packet fields, but fail to do so with BOOTP fields.

receivedIP = 0
conf.checkIPaddr = False
fam,hw = get_if_raw_hwaddr(conf.iface)
dhcp_discover = Ether(dst="ff:ff:ff:ff:ff:ff")/IP(src="0.0.0.0",dst="255.255.255.255")/UDP(sport=68,dport=67)/BOOTP(chaddr=hw)/DHCP(options=[("message-type","discover"),"end"])
ansD,unans = srp(dhcp_discover, multi=True)

if True:
dhcp_request=Ether(dst="ff:ff:ff:ff:ff:ff")/IP(src="0.0.0.0",dst="255.255.255.255")/UDP(sport=68,dport=67)/BOOTP(chaddr=hw,yiaddr=ansD[BOOTP].yiaddr)/DHCP(options=[("message-type","request"),"end"])
ansR, unans = srp(dhcp_request,multi=True)

Object Error 'list' object has no attribute 'yiaddr'

Nimantha
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Wilky
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1 Answers1

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I figured it out not two seconds after posting but hopefully this helps others in the future.

I used srp() instead of srp1(), the former returns multiple packets so I would need to index the specific packet I wanted to look at ansD[0][BOOTP].yiaddr . I have since changed my code to use srp1 instead since this is a DHCP request expecting only one specific "Offer" reply from the DHCP server. Fixed code below

import sys
from scapy.all import *


receivedIP = 0
conf.checkIPaddr = False
fam,hw = get_if_raw_hwaddr(conf.iface)
dhcp_discover=Ether(dst="ff:ff:ff:ff:ff:ff")/IP(src="0.0.0.0",dst="255.255.255.255")/UDP(sport=68,dport=67)/BOOTP(chaddr=hw)/DHCP(options=[("message-type","discover"),"end"])
ansD = srp1(dhcp_discover, multi=True)
if True:
//Request using the IP the server offered us in ansD[BOOTP].yiaddr    

    dhcp_request = Ether(dst="ff:ff:ff:ff:ff:ff")/IP(src="0.0.0.0",dst="255.255.255.255")/UDP(sport=68,dport=67)/BOOTP(chaddr=hw,yiaddr=ansD[BOOTP].yiaddr)/DHCP(options=[("message-type","request"),"end"])
    ansR, unans = srp(dhcp_request,multi=True)
    ansR.summary()
Wilky
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