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Special Forums IP Networking DHCP server also acting as relay Post 302346741 by tomwolf on Monday 24th of August 2009 03:34:29 AM
Old 08-24-2009
How would the following scenario work?

Thanks for the answer. I still have some questions :-)

A client sends a DHCPDISCOVER to the router that acts both as a server and a relay. The server responds with a DHCPOFFER to the client and forwards the broadcast to the server specified in the relay, which also responds with a DHCPOFFER.
If the time difference between the arrival of the the DHCPOFFER messages from the two servers to the client is negligible, which one would the client use?
If the time difference is not negligible, then by the time the client gets the DHCPOFFER from the farther server, it will already have negotiated a lease with the server in it's segment.
I am still having trouble understanding what is the point of having both server and relay in the same machine.
 

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dhcp6r(8)						      System Manager's Manual							 dhcp6r(8)

NAME
dhcp6r - DHCPv6 relay agent SYNOPSIS
dhcp6r [ -d ] [ client-options ] [ server-options ] DESCRIPTION
dhcp6r acts as DHCPv6 relay agent forwarding DHCPv6 messages from clients to servers and vice versa. DHCPv6 messages from clients are received at UDP port 547, they are forwarded to one or more DHCPv6 servers by multicast and/or unicast. DHCPv6 messages from servers to clients are also received at UDP port 547 and forwarded by unicast only. DHCPv6 messages received by multicast at a certain IPv6 interface are never forwarded by multicast to the same interface. If no options are present, the relay agent receives messages by unicast and multicast at all IPv6 interfaces, and all messages are for- warded to all IPv6 interfaces by multicast with the exception mentioned in the previous paragraph. If one or more client-options are present, then messages are only received as specified by the client options. If one or more server- options are present, then messages are only forwarded as specified by the server options. CLIENT-OPTIONS If no client-options are present, the relay receives messages by multicast and unicast at all IPv6 interfaces. If one or more client options are present, then messages are only received as specified by the client-options. In any case, the relay receives client messages by unicast. -cu This option can be used to configure the client such that it receives messages from clients or other relay agents by unicast only. It does not have any effect if a -cm option is present. -cm INTERFACE Accept client messages multicasted at IPv6 interface INTERFACE. The others are receiving only unicast messages. For specifying a set of interfaces, an instance of this option is required for each interface. SERVER-OPTIONS If no server-options are present, the relay forwards messages received from clients by multicast and unicast to all IPv6 interfaces, except the one, which the packet was received on. If one or more server-options are present, then messages are forwarded as specified by the server-options. -sm INTERFACE Forward all received client messages by multicast at IPv6 interface INTERFACE. For specifying a set of interfaces, an instance of this option is required for each interface. -su ADDRESS Forward all received client messages by unicast to the IPv6 address ADDRESS. For specifying a set of addresses, an instance of this option is required for each address. -sf INTERFACE+ADDRESS Forward all received client messages by unicast to the IPv6 address ADDRESS through the IPv6 interface INTERFACE. For specifying a set of combinations of interfaces and addresses, an instance of this option is required for each combination. The -sm, -su, and -sf options can be combined in arbitrary ways. OTHER OPTIONS
-d If this option is not present, dhcp6r will dump logging information into the file /var/log/dhcp6r.log. If the option is present, logging information will be sent to stderr instead. EXAMPLES
The following examples are shown as given to the shell: dhcp6r Receive messages from clients at all IPv6 interfaces by multicast and by unicast, and forward them to all (other) IPv6 interfaces by multicast. dhcp6r -cu Receive messages from clients by unicast only, and forward them to all (other) IPv6 interfaces by multicast. dhcp6r -cm eth0 -cm eth2 Receive messages from clients at interfaces eth0 and eth2 by multicast and by unicast, and forward them to all IPv6 interfaces by multicast (except the one at which the message was received by multicast). dhcp6r -cm eth0 -cm eth2 -sm eth1 Receive messages from clients at interfaces eth0 and eth2 by multicast and by unicast, and forward them to interfaces eth1 by multi- cast. dhcp6r -su fec0::204:ce33:763f:b34 -su fec0::504:ff33:73f:c557 Receive messages from clients at all IPv6 interfaces by multicast and by unicast, and forward a copy of them to each of the speci- fied addresses. dhcp6r -sm eth1 -su fec0::204:ce33:763f:b34 Receive messages from clients at all IPv6 interfaces by multicast and by unicast, and forward them to interface eth1 by multicast and to the specified unicast address. dhcp6r -sm eth1 -sf eth0+fec0::504:ff33:73f:c557 Receive messages from clients at all IPv6 interfaces by multicast and by unicast, and forward them to interface eth1 by multicast and to the specified unicast address. For the unicast address it is enforced that the message will be sent through interface eth0. NOTES
For proper operation of dhcp6r, the host must have at least one global/site scope address assigned to each interface. FILES
/var/log/dhcv6r.log /var/run/dhcpv6/dhcp6r.pid BUGS
Report bugs via http://fedorahosted.org/dhcpv6/ AUTHORS
See http://fedorahosted.org/dhcpv6/wiki/Authors dhcp6r(8)
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