isc-dhcp-server can't get DHCPDISCOVER packet from some clients whose MAC address not in the subnet

VictorLee

10/29/22, 2:41 PM

isc-dhcp-server running normal, it can offer IP address to most clients in all subnet which are defined in the dhcpd.conf file, but it can't receive some DHCPDISCOVER packet from several clients which also in the same define subnet without the static MAC address config.

Some segment of dhcpd.conf:

subnet 10.10.10.0 netmask 255.255.255.0 {
        option routers 10.10.10.1;
        next-server 10.10.10.100;
        filename "pxelinux.0";
        host 10-10-10-72 {hardware ethernet     BB:BB:BB:BB:BB:BF;fixed-address 10.10.10.72;}
        host 10-10-10-73 {hardware ethernet     BB:BB:BB:BB:BB:B0;fixed-address 10.10.10.73;}}

FYI. All subnet config are static define, the clients which can't send DHCPDISCOVER to isc-dhcp-server owns MAC address are not included the dhcpd.conf.

/var/log/message the default dhcp server's log can't get the DHCPDISCOVER request log.

After add the new MAC address's config to dhcpd.conf, then restart isc-dhcp-server, it works for all clients.

What is the base principle of isc-dhcp-server?

Maybe there are not define the MAC address configure of the request client in the dhcpd.conf file?

Or there are not exist the dynamic address range in the subnet config?

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berndbausch

10/29/22, 3:11 PM

So you are saying that DHCP works as expected after you fixed the syntax errors in dhcpd.conf. And you seem to be surprised. I would be surprised of the opposite: If it worked with syntax errors.

VictorLee

10/30/22, 2:57 AM

@berndbausch update the question, plz check.

berndbausch

10/30/22, 5:08 AM

You mean you define a subnet without explicitly stating MAC addresses. Some clients don't get a DHCP response, and you see no trace of DHCPDISCOVERY in /var/log/messages. Once you add those MAC addresses explicitly, as shown in the snippet you provide, the clients do get a DHCP response, and you see expected messages in the log file. Did I understand that right? I don't think anybody can help you without seeing your dhcpd.conf.

VictorLee

10/30/22, 5:45 AM

@berndbausch yes, you understand me. I could get the bootps request by `tcpdump port 67 or port 68 | grep 'the MAC address'` always, but not in `/var/log/messages` before add those MAC address explicitly in **dhcpd.conf**.

Elon Musk

I sit in a Tesla and translated this thread with Ai:

EN: isc-dhcp-server can't get DHCPDISCOVER packet from some clients whose MAC address not in the subnet

TH: isc-dhcp-server ไม่สามารถรับแพ็กเก็ต DHCPDISCOVER จากไคลเอนต์บางตัวที่มีที่อยู่ MAC ไม่ได้อยู่ในซับเน็ต

RO: isc-dhcp-server nu poate obține pachetul DHCPDISCOVER de la unii clienți a căror adresă MAC nu este în subrețea

RU: isc-dhcp-server не может получить пакет DHCPDISCOVER от некоторых клиентов, MAC-адрес которых не входит в подсеть

VI: isc-dhcp-server không thể nhận gói DHCPDISCOVER từ một số máy khách có địa chỉ MAC không có trong mạng con

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