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1 What to do if your BIND or DHCP server has crashed Featured

If your BIND or DHCP server crashes (i.e. the daemon terminates unexpectedly), collecting the evidence available and submitting to us is vital if we are to help diagnose the problem and provide a solution. Below is a list of files/information to collect after…

2 LDAP and updating to DHCP 4.3.3 or newer

The LDAP integration code for ISC DHCP was originally contributed to ISC and for the most part has not been directly supported by ISC staff. Bugs reported against it were left to be addressed by contributors and with our limited development resources the…

3 Why is my server logging: "dhcpd: icmp_echorequest 192.0.2.1: No buffer space available"?

dhcpd: icmp_echorequest 192.0.2.1: No buffer space available The kernel has returned an error ENOBUFS to dhcpd in response to the ICMP (ping) message that dhcpd sends with ping-check enabled. This means that the socket send buffer has overflowed (dhcpd is…

4 Why is my server logging: "dhcpd: send_packet: Invalid argument"?

dhcpd: send_packet: Invalid argument dhcpd: dhcp.c:3730: Failed to send 300 byte long packet over fallback interface. This error message is seen due to two different problems: The server has a resource problem - specifically that the ARP cache (sometimes…

5 DHCPv6 "not our server identifier", discarding renews

Question: Why am I seeing lots of "Discarding Renew ... not our server identifier" messages in logs after a server hardware (or OS) upgrade? Example: Renew message from fe80::250:56ff:fe32:202 port 546, transaction ID 0x17D67300 Discarding Renew from fe80::250:56ff:fe32:202;…

6 After sending a DHCPOFFER packet to a client, how long will dhcpd wait before discarding that offer?

dhcpd holds the lease for 2 minutes after sending a DHCPOFFER. A short lease is assigned before the offer is made and the default timeout for that initial lease is 2 minutes. If (or when) the client requests the lease, then the updated lease has a duration…

7 Migration Tips For Upgrading From DHCP 3 to DHCP 4

ISC is ending support for DHCP 3.1-ESV, the last supported version of the DHCP 3 family of software releases. Customers who wish to use a supported version of the software are advised to consult the DHCP versions page and select a "Current" or "Extended Support…

8 How do I resynchronize a failover pair?

There are various reasons for wanting to resynchronize a failover pair of DHCP servers. These include: Hardware failure - one server is offline for a long time while it is replaced Configuration error (changes or migrations) causing issues such as both servers…

9 Sending a Server Shutdown Message Via OMAPI

OMAPI is the control channel specification for dhcpd and you can use it to modify the config of a running server by adding host objects, subnets, etc. You can also use it to send control messages to the server, for example to put a server in failover mode…

10 Why does DHCP use raw sockets?

The DHCP protocol has some specific requirements to really work properly - in particular being able to transmit to and receive packets sent to the all-ones limited broadcast address (255.255.255.255), and being able to send a unicast without an ARP. It's…

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