dhcp douts

dhcp douts

Post by RajaSekhar.Kavu » Fri, 08 Apr 2005 21:36:25


        when a dhcp client sends a dhcp request and get the dhcp offer
from the server.that offer will be a unicast packet or again a broad
cast packet.please tell me if there is no dhcp server in the network
and still we start the client how much time it will wait.

thanking you


dhcp douts

Post by Horst Knobloc » Sat, 09 Apr 2005 03:54:40

>         when a dhcp client sends a dhcp request and get the dhcp offer
> from the server.

If a dhcp request is sent the server answers with
dhcp ack or dhcp nak, not with a dhcp offer. See
state diagram (Fig. 5) in RFC2131.

I assume you mean client sends dhcp discover and server
sends dhcp offer.

Quote:> that offer will be a unicast packet or again a broad
> cast packet.

It depends on the contents of the received dhcp discover
message and whether the message was relayed via a bootp
relay. See RFC 2131 4.1 Constructing and sending DHCP

| ...
|  If the 'giaddr'
|  field is zero and the 'ciaddr' field is nonzero, then the server
|  unicasts DHCPOFFER and DHCPACK messages to the address in 'ciaddr'.
|  If 'giaddr' is zero and 'ciaddr' is zero, and the broadcast bit is
|  set, then the server broadcasts DHCPOFFER and DHCPACK messages to
|  0xffffffff. If the broadcast bit is not set and 'giaddr' is zero and
|  'ciaddr' is zero, then the server unicasts DHCPOFFER and DHCPACK
|  messages to the client's hardware address and 'yiaddr' address.  In
|  all cases, when 'giaddr' is zero, the server broadcasts any DHCPNAK
|  messages to 0xffffffff.
| ...

Note that a giaddr of nonzero indicates that the client
message was relayed via a (bootp) relay agent.

Ciao, Horst
?When pings go wrong (It hurts me too)? E.Clapton/E.James/P.Tscharn


1. RH 5.1 flawless ftp-dhcp install; dhcp config retained; dhcp fails @ boot

DHCP fails to configure a network connection, even after it worked
wonderfully for an ftp install of RH 5.1 and I retained the network
configuration during the install process.  The relevant message on the
console during bootup is: DHCP ... failed.  The only message in
/var/log/messages that appears to be relevant is "no DHCPOFFER".
/sbin/ifconfig lists nothing for eth0.

A number of modules relevant to DHCP are loaded. I assume that all
necessary modules have been loaded.  The eithernet card also appears
to be correctly recognized.

I've read but not yet tried the Red Hat hacks listed in the DHCPcd
mini-HOWTO.  Has anyone successfully used these on RH 5.1?



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