[Dnsmasq-discuss] dnsmasq DHCP behind a DHCP relay, without directly-connected addresses

Simon Kelley simon at thekelleys.org.uk
Wed Aug 3 22:57:03 BST 2016


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"dnsmasq-dhcp: 1302931552 DHCPDISCOVER(bond0) 00:aa:bb:cc:dd:ee ignored"

Implies that you've somehow configured dnsmasq to ignore this client,
either with

dhcp-host=<stuff to id client>,ignore

or

dhcp-ignore=<some tags>


Maybe take a look at the rest of the config you didn't post or post it
here? Fixing this problem is necessary before looking at the subnet
address selection stuff, which should be possible using a DHCP relay.

Cheers,

Simon.



On 02/08/16 23:43, James Brown wrote:
> I have a setup roughly like the following ASCII-art diagram
> (numbers and number of VLANs simplified greatly):
> 
> 
> |===== VLAN 1 : 10.0.1.0/24  ======|    |============== VLAN 2:
> 10.0.2.0/24 ==============| |                                  |
> | | |   |------------------|        |-------------| | |   |
> admin host   |        |  gateway    | | |   |    10.0.1.2/24   |
> | 10.0.1.1/24 | |----------------------------|      | |
> |------------------|        | 10.0.2.1/24 |       |   client host |
> | |                               | etc         |       | should
> get static lease of |      | |
> |-------------|       | 10.0.2.x |      | |
> |    | |----------------------------|      | 
> |==================================| 
> |=================================================|
> 
> ?We have multiple VLANs each of which has its own subnet. They're
> bridged by a single multi-homed gateway (actually, an HA pair of
> them, but whatever). The gateway is running dhrelay3 and forwarding
> DHCP requests to the admin host in the administrative VLAN, which
> is running dnsmasq with a database of addresses to hand out.? I
> would prefer to be able to avoid having to put that database on the
> gateway and have a bunch of dynamic host configuration on a router.
> The admin host is single-homed.
> 
> The dnsmasq config looks like the following (I've removed most of
> the entries and config to simplify the question):
> 
> port = 0 dhcp-range=10.0.1.0,static,255.255.255.0 
> dhcp-range=10.0.2.0,static,255.255.255.0 dhcp-option=6,10.0.2.3 
> dhcp-option=3,10.0.2.1 dhcp-host=00:aa:bb:cc:dd:ee,10.2.0.86
> 
> Unfortunately, dnsmasq seems to refuse to hand out addresses from
> a non-directly-connected subnet. When the requests come in from 
> 00:aa:bb:cc:dd:ee, I just get the following logged:
> 
> dnsmasq: started, version 2.76 DNS disabled dnsmasq: compile time
> options: IPv6 GNU-getopt no-DBus no-i18n no-IDN DHCP DHCPv6 no-Lua
> TFTP no-conntrack ipset auth no-DNSSEC loop-detect inotify 
> dnsmasq-dhcp: DHCP, static leases only on 10.0.1.0, lease time 1h 
> dnsmasq-dhcp: DHCP, static leases only on 10.0.2.0, lease time 1h 
> dnsmasq-dhcp: DHCP, static leases only on 10.0.3.0, lease time 1h 
> dnsmasq-dhcp: 1302931552 available DHCP subnet:
> 10.0.1.0/255.255.255.0 dnsmasq-dhcp: 1302931552 DHCPDISCOVER(bond0)
> 00:aa:bb:cc:dd:ee ignored dnsmasq-dhcp: 1302931552 available DHCP
> subnet: 10.0.1.0/255.255.255.0 dnsmasq-dhcp: 1302931552
> DHCPDISCOVER(bond0) 00:aa:bb:cc:dd:ee ignored dnsmasq-dhcp:
> 4279941416 available DHCP subnet: 10.0.1.0/255.255.255.0 
> dnsmasq-dhcp: 4279941416 DHCPDISCOVER(bond0) 00:aa:bb:cc:dd:ee
> ignored
> 
> ?Tcpdump of the packets being received by ?the host look roughly
> like the following:
> 
> 22:23:57.987953 IP (tos 0x0, ttl 64, id 48608, offset 0, flags
> [DF], proto UDP (17), length 328) 10.0.1.1.bootps > admin.bootps:
> BOOTP/DHCP, Request from 00:aa:bb:cc:dd:ee (oui Unknown), length
> 300, hops 1, xid 0x4ec4ba20, secs 24, Flags [none] Gateway-IP
> 10.0.1.1 Client-Ethernet-Address 00:aa:bb:cc:dd:ee (oui Unknown) 
> Vendor-rfc1048 Extensions Magic Cookie 0x63825363 DHCP-Message
> Option 53, length 1: Discover Parameter-Request Option 55, length
> 13: Subnet-Mask, BR, Time-Zone, Classless-Static-Route Domain-Name,
> Domain-Name-Server, Hostname, YD YS, NTP, MTU, Option 119 
> Default-Gateway
> 
> ?I would like for the admin host (10.0.1.1/24) to be able to hand
> out IP addresses to hosts in any VLAN without having to multi-home
> it. Is this just impossible in dnsmasq, or is there some magic
> option that will tell it to hand out IP addresses on a
> non-connected subnet when the request goes through a relay?
> 
> I've attempted to go through the source code, but even once I
> figured out the idiosyncratic indentation style of rfc2131.c, I
> still can't figure out precisely where the logic to generate this
> message lives.
> 
> ?Thanks for any help y'all can provide.?
> 
> 
> 
> _______________________________________________ Dnsmasq-discuss
> mailing list Dnsmasq-discuss at lists.thekelleys.org.uk 
> http://lists.thekelleys.org.uk/mailman/listinfo/dnsmasq-discuss
> 
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