[Dnsmasq-discuss] assigning IP addresses to secondary subnets on the same vlan via dhcp relay

znuffy at gmail.com znuffy at gmail.com
Sat Nov 19 22:00:19 UTC 2022 

Hello,

I've been struggling with this issue for over a year, and I'm still
not sure if this is a limitation of dnsmasq or I'm doing something
wrong.

Situation:

- core switch (Brocade)
- dnsmasq 2.87 running on a VM, IP address 10.11.19.20/24
- the core switch is configured to use the dnsmasq box as an "ip
helper" (ie: dhcp relay)
- we have multiple /24's on specific VLANs

The issue is that we can NOT assign IPs to any other than the primary
subnet of the vlan (ve interface) -- hence forward as BB.BB.93.5/24

Relevant config of the interface on the switch:

    SSH at core01(config-vif-501)#sh run int ve 501
    interface ve 501
    vrf forwarding core01
    ip address AA.AA.152.1 255.255.255.0
    ip address AA.AA.153.1 255.255.255.0
    ip address AA.AA.155.1 255.255.255.128
    ip address BB.BB.18.1 255.255.255.0
    ip address BB.BB.93.1 255.255.255.0
    no ip redirect
    ip helper-address 1 10.11.19.20
    --- snip ---
    !

Relevant dnsmasq config:

    # Don't function as a DNS server:
    port=0
    log-dhcp

    shared-network=10.11.19.20,AA.AA.152.0

    # TFTP Configuration
    enable-tftp
    tftp-root=/srv/pxe
    # -- removed irrelevant bootp/tftp stuff

    # Set ranges and tags
    dhcp-range=set:405,10.11.19.0,static,255.255.255.0,1h

    dhcp-range=set:501a,AA.AA.152.0,static,255.255.255.0,5m
    dhcp-range=set:501b,AA.AA.153.0,static,255.255.255.0,5m
    dhcp-range=set:501c,AA.AA.155.0,static,255.255.255.128,5m
    dhcp-range=set:501d,BB.BB.18.1,static,255.255.255.0,5m
    dhcp-range=set:501e,BB.BB.93.0,static,255.255.255.0,5m

    # Set Netmask
    dhcp-option=tag:405,option:netmask,255.255.255.0

    dhcp-option=tag:501a,option:netmask,255.255.255.0
    dhcp-option=tag:501b,option:netmask,255.255.255.0
    dhcp-option=tag:501c,option:netmask,255.255.255.128
    dhcp-option=tag:501d,option:netmask,255.255.255.0
    dhcp-option=tag:501e,option:netmask,255.255.255.0

    # Set default gateway
    dhcp-option=tag:405,option:router,10.11.19.1

    dhcp-option=tag:501a,option:router,AA.AA.152.1
    dhcp-option=tag:501b,option:router,AA.AA.153.1
    dhcp-option=tag:501c,option:router,AA.AA.155.1
    dhcp-option=tag:501d,option:router,BB.BB.18.1
    dhcp-option=tag:501e,option:router,BB.BB.93.1

    # --- hosts ---
    dhcp-host=00:50:56:86:71:14,BB.BB.93.5,pxe-host

This results into the following message in the logs:

Nov 19 23:51:02 dnsmasq[1611436]: started, version 2.87 DNS disabled
Nov 19 23:51:02 dnsmasq[1611436]: compile time options: IPv6
GNU-getopt DBus no-UBus i18n IDN DHCP DHCPv6 no-Lua TFTP conntrack
ipset nftset auth cryptohash DNSSEC loop-detect inotify dumpfile
Nov 19 23:51:02 dnsmasq-dhcp[1611436]: DHCP, static leases only on
AA.AA.155.0, lease time 5m
Nov 19 23:51:02 dnsmasq-dhcp[1611436]: DHCP, static leases only on
BB.BB.93.0, lease time 5m
Nov 19 23:51:02 dnsmasq-dhcp[1611436]: DHCP, static leases only on
BB.BB.18.1, lease time 5m
Nov 19 23:51:02 dnsmasq-dhcp[1611436]: DHCP, static leases only on
AA.AA.155.0, lease time 5m
Nov 19 23:51:02 dnsmasq-dhcp[1611436]: DHCP, static leases only on
AA.AA.153.0, lease time 5m
Nov 19 23:51:02 dnsmasq-dhcp[1611436]: DHCP, static leases only on
AA.AA.152.0, lease time 5m
Nov 19 23:51:02 dnsmasq-dhcp[1611436]: DHCP, static leases only on
10.11.19.0, lease time 1h
Nov 19 23:51:02 dnsmasq-tftp[1611436]: TFTP root is /srv/pxe
Nov 19 23:51:07 dnsmasq-dhcp[1611436]: 388452072 available DHCP
subnet: AA.AA.152.0/255.255.255.0
Nov 19 23:51:07 dnsmasq-dhcp[1611436]: 388452072 vendor class:
PXEClient:Arch:00007:UNDI:003000
Nov 19 23:51:07 dnsmasq-dhcp[1611436]: 388452072 DHCPDISCOVER(ens160)
00:50:56:86:71:14 no address available
Nov 19 23:51:11 dnsmasq-dhcp[1611436]: 388452072 available DHCP
subnet: AA.AA.152.0/255.255.255.0
Nov 19 23:51:11 dnsmasq-dhcp[1611436]: 388452072 vendor class:
PXEClient:Arch:00007:UNDI:003000
Nov 19 23:51:11 dnsmasq-dhcp[1611436]: 388452072 DHCPDISCOVER(ens160)
00:50:56:86:71:14 no address available
Nov 19 23:51:19 dnsmasq-dhcp[1611436]: 388452072 available DHCP
subnet: AA.AA.152.0/255.255.255.0
Nov 19 23:51:19 dnsmasq-dhcp[1611436]: 388452072 vendor class:
PXEClient:Arch:00007:UNDI:003000
Nov 19 23:51:19 dnsmasq-dhcp[1611436]: 388452072 DHCPDISCOVER(ens160)
00:50:56:86:71:14 no address available
Nov 19 23:51:35 dnsmasq-dhcp[1611436]: 388452072 available DHCP
subnet: AA.AA.152.0/255.255.255.0
Nov 19 23:51:35 dnsmasq-dhcp[1611436]: 388452072 vendor class:
PXEClient:Arch:00007:UNDI:003000
Nov 19 23:51:35 dnsmasq-dhcp[1611436]: 388452072 DHCPDISCOVER(ens160)
00:50:56:86:71:14 no address available

Relevant tpcdump of the received DHCP Package:

23:51:02.144340 08:35:71:f0:fa:c1 > 00:50:56:a6:fd:79, ethertype IPv4
(0x0800), length 389: (tos 0x1,ECT(1), ttl 63, id 16378, offset 0,
flags [none], proto UDP (17), length 375)
    10.11.20.1.67 > 10.11.19.20.67: [udp sum ok] BOOTP/DHCP, Request
from 00:50:56:86:71:14, length 347, hops 1, xid 0xbb4e1961, secs 28,
Flags [Broadcast] (0x8000)
          Gateway-IP AA.AA.152.1
          Client-Ethernet-Address 00:50:56:86:71:14
          Vendor-rfc1048 Extensions
            Magic Cookie 0x63825363
            DHCP-Message Option 53, length 1: Discover
            MSZ Option 57, length 2: 1472
            Parameter-Request Option 55, length 35:
              Subnet-Mask, Time-Zone, Default-Gateway, Time-Server
              IEN-Name-Server, Domain-Name-Server, Hostname, BS
              Domain-Name, RP, EP, RSZ
              TTL, BR, YD, YS
              NTP, Vendor-Option, Requested-IP, Lease-Time
              Server-ID, RN, RB, Vendor-Class
              TFTP, BF, GUID, Option 128
              Option 129, Option 130, Option 131, Option 132
              Option 133, Option 134, Option 135
            GUID Option 97, length 17:
0.66.6.201.133.10.9.24.55.187.178.66.116.65.71.167.235
            NDI Option 94, length 3: 1.3.0
            ARCH Option 93, length 2: 7
            Vendor-Class Option 60, length 32:
"PXEClient:Arch:00007:UNDI:003000"

Any help/suggestions on what to do next? Is this just a
misconfiguration issue on my side or it's something that dnsmasq
can't/won't do?

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