[Dnsmasq-discuss] dnsmasq does not answer dhcp requests

Albert ARIBAUD albert.aribaud at free.fr
Thu Jun 4 13:15:02 BST 2015


Hi Tom,

Le Thu, 4 Jun 2015 07:26:55 -0400, Tom Tomson <nobolomo at gmail.com> a
écrit :

> Hi everybody,
> 
> although I am apparently not the only one with problems like these. Still,
> I have not found a solution by looking through the list - that's why I am
> posting this mail. Sorry, if I should have overseen any important hint -
> feel free to point me to the right direction...
> 
> So, here is my issue:
> 
> I have set up my (Debian based) Kali system (Linux kali 3.18.0-kali3-amd64
> #1 SMP Debian 3.18.6-1~kali2 (2015-03-02) x86_64 GNU/Linux) to provide a
> wireless access point with hostapd (v1.0). To provide clients with IP
> addresses, I am using dnsmasq (version 2.62).
> 
> The configured SSID gets advertised and when I connect to it (e.g. with my
> smartphone) the device will be briefly authenticated and immediately
> deauthenticated.
> 
> tail -f /var/log/syslog
> Jun  3 18:33:04 kali hostapd: wlan1: STA d8:96:95:27:30:b4 IEEE 802.11:
> authenticated
> Jun  3 18:33:04 kali hostapd: wlan1: STA d8:96:95:27:30:b4 IEEE 802.11:
> associated (aid 1)
> Jun  3 18:33:04 kali hostapd: wlan1: STA d8:96:95:27:30:b4 RADIUS: starting
> accounting session 556F807A-00000000
> Jun  3 18:33:06 kali hostapd: wlan1: STA d8:96:95:27:30:b4 IEEE 802.11:
> disassociated
> Jun  3 18:33:07 kali hostapd: wlan1: STA d8:96:95:27:30:b4 IEEE 802.11:
> deauthenticated due to inactivity
> 
> Apparently this deauthentication is due to the device not getting an IP
> address via DHCP. When I look for network traffic on the wifi interface, I
> will see the DHCP requests:
> 
> # tcpdump -i wlan1 ip
> tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
> listening on wlan1, link-type EN10MB (Ethernet), capture size 65535 bytes
> 18:33:04.694155 IP 0.0.0.0.bootpc > 255.255.255.255.bootps: BOOTP/DHCP,
> Request from d8:96:95:27:30:b4 (oui Unknown), length 300
> 18:33:04.694254 IP 0.0.0.0.bootpc > 255.255.255.255.bootps: BOOTP/DHCP,
> Request from d8:96:95:27:30:b4 (oui Unknown), length 300
> 18:33:06.172565 IP 0.0.0.0.bootpc > 255.255.255.255.bootps: BOOTP/DHCP,
> Request from d8:96:95:27:30:b4 (oui Unknown), length 300
> 18:33:06.172641 IP 0.0.0.0.bootpc > 255.255.255.255.bootps: BOOTP/DHCP,
> Request from d8:96:95:27:30:b4 (oui Unknown), length 300
> 
> In the dnsmasq log I can see the corresponding requests:
> 
> # tail -f /var/log/dnsmasq.log
> Jun  3 17:57:59 dnsmasq[11398]: exiting on receipt of SIGTERM
> Jun  3 17:58:01 dnsmasq[11511]: started, version 2.62 cachesize 150
> Jun  3 17:58:01 dnsmasq[11511]: compile time options: IPv6 GNU-getopt DBus
> i18n IDN DHCP DHCPv6 no-Lua TFTP conntrack
> Jun  3 17:58:01 dnsmasq[11511]: warning: no upstream servers configured
> Jun  3 17:58:01 dnsmasq-dhcp[11511]: DHCP, IP range 10.0.0.10 --
> 10.0.0.250, lease time 12h
> Jun  3 17:58:01 dnsmasq[11511]: read /etc/hosts - 5 addresses
> Jun  3 18:33:04 dnsmasq-dhcp[11511]: 151532460 available DHCP range:
> 10.0.0.10 -- 10.0.0.250
> Jun  3 18:33:04 dnsmasq-dhcp[11511]: 151532460 client provides name: iTC
> Jun  3 18:33:06 dnsmasq-dhcp[11511]: 151532460 available DHCP range:
> 10.0.0.10 -- 10.0.0.250
> Jun  3 18:33:06 dnsmasq-dhcp[11511]: 151532460 client provides name: iTC
> 
> So, the DHCP requests apparently reach the dnsmasq daemon - however this
> guy is not responding in any way. But why???
> 
> Here is my dnsmasq config:
> 
> # cat /etc/dnsmasq.conf
> log-facility=/var/log/dnsmasq.log
> interface=wlan1
> dhcp-range=10.0.0.10,10.0.0.250,12h
> dhcp-option=1,255.255.255.0
> dhcp-option=3,10.0.0.1
> dhcp-option=6,10.0.0.1
> log-queries
> log-dhcp

What are the configurations of the wlan1 and eth0 interfaces ?

> iptables is configured to forward traffic from the wifi interface to eth0,
> but has no other restrictions:

This does not "forward traffic from the wifi interface to eth0", this
just forwards anything (policy is ACCEPT); the wlan1/eth0 specific
line does nothing. Besides, what is the point of forwarding traffic
from wlan1 to eth0? Either packets incoming on wlan1 all have a
destination IP in the subnet where eth0 belongs, and the kernel will
route them anyway, r they have a destination outside the eth0 subnet,
and they should not be routed to eth0.

> # iptables -L -v
> Chain INPUT (policy ACCEPT 6784 packets, 9546K bytes)
>  pkts bytes target     prot opt in     out     source
> destination
> Chain FORWARD (policy ACCEPT 0 packets, 0 bytes)
>  pkts bytes target     prot opt in     out     source
> destination
>     0     0 ACCEPT     all  --  wlan1  eth0    anywhere
> anywhere
> Chain OUTPUT (policy ACCEPT 6900 packets, 923K bytes)
>  pkts bytes target     prot opt in     out     source
> destination
> 
> Is there any way to get more debugging information? Or does anybody on this
> list have a solution to this strange behaviour?
> 
> Any help is greatly appreciated!
> 
> Regards,
> Tom


Amicalement,
-- 
Albert.



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