[Dnsmasq-discuss] no reaction on dhcp request

Roman Zimmermann ladoo at gmx.at
Thu Sep 21 17:40:04 BST 2006


hi!

I recently ran into a rather disturbing problem issue while trying to
configure dnsmasq as a dhcp server.

I have it running as a dns-server for some time now and never had any
issues. Then i simply set some dhcp-x config variables and tried but it
simply did nothing when a request came in and I've been unable to
determine why...

These are the steps that I took to narrow the cause:

- I checked the logs - nothing there.
- I tried another dhcp-server (udhcpd) and it worked fine on the same
machine
- I checked whether dnsmasq is listening on the right port
# netstat -lup | grep bootps
udp  0  0 *:bootps  *:*  13975/dnsmasq

- I checked the network communication with tcpdump and it showed only
the incomming broadcast but no response

- I used strace (strace dnsmasq -dq) to see if there is something coming
in when the request arrives. And indeed something happened:

# dnsmasq -dq
dnsmasq: started, version 2.31 cachesize 150
dnsmasq: compile time options: IPv6 GNU-getopt no-ISC-leasefile no-DBus
no-I18N
dnsmasq: DHCP, IP range 192.168.0.128 -- 192.168.0.254, lease time 3d
dnsmasq: using local addresses only for domain zimmermann.local
dnsmasq: reading /etc/ppp/resolv.conf
dnsmasq: using nameserver x.x.x.x#53
dnsmasq: using nameserver x.x.x.x#53
dnsmasq: using local addresses only for domain zimmermann.local
dnsmasq: read /etc/hosts - 5 addresses

[many lines here after start]

) = 1 (in [6])
time(NULL)                              = 1158856108
stat64("/etc/ppp/resolv.conf", {st_mode=S_IFREG|0644, st_size=52, ...})
= 0
recvmsg(6, {msg_name(0)=NULL, msg_iov(1)=[{"\1\1\6\0\f\276\22E\0\0\0\0
\300\250\0\25\0\0\0\0\0\0\0\0"..., 548}], msg_controllen=24,
{cmsg_len=24, cmsg_level=SOL_IP, cmsg_type=, ...}, msg_flags=0},
MSG_PEEK) = 250
recvmsg(6, {msg_name(16)={sa_family=AF_INET, sin_port=htons(68),
sin_addr=inet_addr("192.168.0.21")}, msg_iov(1)=[{"\1\1\6\0\f\276\22E\0
\0\0\0\300\250\0\25\0\0\0\0\0\0\0\0"..., 548}], msg_controllen=24,
{cmsg_len=24, cmsg_level=SOL_IP, cmsg_type=, ...}, msg_flags=0}, 0) =
250
ioctl(6, SIOCGIFNAME, {ifr_index=2, ifr_name="eth0"}) = 0
ioctl(6, SIOCGIFADDR, {ifr_name="eth0", ifr_addr={AF_INET,
inet_addr("192.168.0.127")}}) = 0
sendto(3, "\24\0\0\0\26\0\5\3\3\0\0\0\0\0\0\0\2@\0\0", 20, 0,
{sa_family=AF_NETLINK, pid=0, groups=00000000}, 12) = 20
recvmsg(3, {msg_name(0)=NULL, msg_iov(1)=[{"D\0\0\0\24\0\2\0\3\0\0\0
\0227\0\0\2\10\200\376\1\0\0\0"..., 400}], msg_controllen=0,
msg_flags=0}, MSG_PEEK) = 316
recvmsg(3, {msg_name(0)=NULL, msg_iov(1)=[{"D\0\0\0\24\0\2\0\3\0\0\0
\0227\0\0\2\10\200\376\1\0\0\0"..., 400}], msg_controllen=0,
msg_flags=0}, 0) = 316
recvmsg(3, {msg_name(0)=NULL, msg_iov(1)=[{"\24\0\0\0\3\0\2\0\3\0\0\0
\0227\0\0\0\0\0\0\1\0\0\0\10\0"..., 400}], msg_controllen=0,
msg_flags=0}, MSG_PEEK) = 20
recvmsg(3, {msg_name(0)=NULL, msg_iov(1)=[{"\24\0\0\0\3\0\2\0\3\0\0\0
\0227\0\0\0\0\0\0\1\0\0\0\10\0"..., 400}], msg_controllen=0,
msg_flags=0}, 0) = 20
select(12, [3 4 5 6 8 11], [], [], NULL <unfinished ...>


Here is my config (without comments):
# grep '^[^#].*' /etc/dnsmasq.conf
domain-needed
bogus-priv
resolv-file=/etc/ppp/resolv.conf
local=/zimmermann.local/
except-interface=ppp0
domain=zimmermann.local
dhcp-range=192.168.0.128,192.168.0.254,72h
dhcp-lease-max=127
mx-host=zimmermann.local,mithril.zimmermann.local,50
mx-target=mithril.zimmermann.local
localmx


Now I really don't know what went wrong, but I hope this list is the
right place to seek help and hopefully find the answer.
Thanks in advance for any help

regards
Roman




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