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1 DHCPv4 Over DHCPv6 (RFC7341) in ISC DHCP 4.3.4 Featured

General In ISC DHCP 4.3.4 we have added experimental support for DHCPv4 Over DHCPv6 as described in RFC7341. This work is designed to aid the transition of the Internet from IPv4 to IPv6. It provides a mechanism for a "v4 island" to get information from a…

2 DHCP uses too much memory: reducing dhcp memory consumption by careful use of range6 statements

Summary: DHCP can use significantly more memory than anticipated for DHCPv6 subnets; how much memory is consumed can be significantly reduced by strategic use of range6 statements, supplemented by static host assignments (real or dummy). There are two options:…

3 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…

4 Standard DHCP Options Defined in ISC DHCP and Kea

These tables showing which standard options are supported in each of ISC DHCP and Kea may be helpful in planning migration from one server to the other. DHCPv4 Options Code Name Reference DHCP 4.3.0+ Kea 1.0+ 0 Pad RFC2132 Yes Yes 1 Subnet Mask RFC2132 Yes…

5 LDAP

General In 4.2.0 we started including some contributed code for storing and retrieving your DHCP configuration in LDAP. This is useful if you have a number of DHCP servers and update their configurations frequently. This code was written by Brian Masney and…

6 DHCPv4 Server Performance

Background In the DHCPv4 server there are two areas of the code that can limit the server's performance - saving lease information to non-volatile storage and manipulating a lease entry within the in-memory data structures. This article discusses some of…

7 Why does "dhclient -6" not work if I haven't already enabled IPv6 on the interface?

IPv6 makes extensive use of the "link-local" address. This address is configured automatically when the interface is brought up. Various IPv6 subprotocols, including Neighbor Discovery Protocol (NDP) and DHCPv6, require and use this address. The IPv6 link-local…

8 Specifying Address Ranges in IPv6

Problem: How do I specify an address range for IPv6? Answer: The instruction range6 provides two ways to define a block of addresses that the server can use for allocations. While either method will work, the server will allocate addresses more efficiently…

9 How to workaround IPv6 prefix length issues with ISC DHCP clients.

In our current DHCP client code (at the time of writing this article: 4.3.0, 4.2.6 and 4.1-ESV-R9) the prefix length associated with an address from an IA_NA or IA_TA is hardcoded to 64. When this code was written this seemed to be an appropriate placeholder…

10 What causes dhcpd to log uid lease 203.0.113.51 for client xx:xx:xx:xx:xx:xx is duplicate ?

Problem: Similar errors to those below may be logged regularly by dhcpd servers operating in a failover pair configuration: Sep 21 22:16:24 dhcpd: [ID 702911 local5.error] uid lease 203.0.113.51 for client xx:xx:xx:xx:xx:xx is duplicate on VLAN001 Sep 21…

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