From: Tomek Mrugalski Date: Tue, 10 Feb 2015 18:57:10 +0000 (+0100) Subject: [3575] Description of v4 conflict resolution updated. X-Git-Tag: trac3723_base~35^2~2 X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=a4a158f98fd85c7162fbbacccc608f40b00fac8a;p=thirdparty%2Fkea.git [3575] Description of v4 conflict resolution updated. --- diff --git a/doc/guide/dhcp4-srv.xml b/doc/guide/dhcp4-srv.xml index b60409c445..3fabb61771 100644 --- a/doc/guide/dhcp4-srv.xml +++ b/doc/guide/dhcp4-srv.xml @@ -1821,7 +1821,7 @@ temporarily override a list of interface names and listen on all interfaces.
Conflicts in DHCPv4 reservations - As reservations and lease information are kept in different places, + As reservations and lease information are kept separately, conflict may arrise. Consider the following series of events. The server has configured 192.0.2.10 to 192.0.2.20 dynamic pool range. Host A requests an address and gets 19.0.2.10. Now the system administrator @@ -1840,6 +1840,7 @@ temporarily override a list of interface names and listen on all interfaces. the server has to temporarily assign a different address (not matching what has been reserved) to host B. + + + When the host A renews its address, the server will discover that + the address being renewed is now reserved for someone else (host + B). Therefore the server will inform the host A that it is no longer + allowed to use it by sending NAK message. The server will remove the + lease, though, as there's small chance that the NAK may be lost if the + network is lossy. If that happens, the client will not receive any + responses, so it will retransmit its Request packet. Once the NAK is + received by the host A, it will then revert to the server discovery and + will eventually get a different address. Besides allocating a new lease, + the server will also remove the old one. As a result the address + 192.0.2.10 will be no longer used. When host B tries to renew its + temporary address, the server will detect that it has a valid lease, but + there is a reservation for a different address. The server will send NAK + to inform host B that its address is no longer usable, but will keep its + least (again, the NAK may be lost, so the server will keep it, until the + client gets back for a new address). The host B will revert to the server + discovery phase and will eventually send a REQUEST message. This time the + server will find out that there is a reservation for that host and the + reserved address 192.0.2.10 is not used, so it will be granted. It will + also remove the lease for the temporary address that the host B previously + had. This recovery will succeed, even if other hosts will attempt to get the reserved address. Had the host C requested address 192.0.2.10 after