dhcp renewal rebinding

[malshara]

hello ,

I just need to know what is the Destination Mac address that should the client send in case renew lease for an IP address ?

Regards

[acampbell]

Hi,

The client will send a dhcp requst packet as ip unicast to the server ip address.
The destibation MAC will either be the DHCP server if on the same Vlan or the clients default gateway
if the server is remote from the client subnet.

Regards
Alex

[malshara]

Hi Alex ,

thanks for your replay ,I have a relay in between so I should expect the mac address for the relay device,but what if the destination mac address is a broadcast ?

Regards

[Rolf Fischer]

Hi,

as far as I understand, DHCP differentiates between RENEWING (T1-Timer, by default 1/2 of total lease time) and REBINDING (T2 Timer expired, by default 7/8 of total lease time).

RFC 2131 4.3.6 Table 4:

---------------------------------------------------------------------
|              |INIT-REBOOT  |SELECTING    |RENEWING     |REBINDING |
---------------------------------------------------------------------
|broad/unicast |broadcast    |broadcast    |unicast      |broadcast |
|server-ip     |MUST NOT     |MUST         |MUST NOT     |MUST NOT  |
|requested-ip  |MUST         |MUST         |MUST NOT     |MUST NOT  |
|ciaddr        |zero         |zero         |IP address   |IP address|
---------------------------------------------------------------------

HTH

Rolf

[malshara]

Hi Rolf,

this is the issue that I can see the destination mac address for the renew DHCP REQUEST as a broadcast and as my information ,it should be a unicast ,I need to understand what make a client to send the destination mac adress as a broadcast since he already has the information for the destination mac address and the ip address for the server .

here am talking about the renew process .

Regards

[Rolf Fischer]

Well, it depends of course on the clients respective DHCP implementation.

The only standard-based explanation I found is this (4.4.4 Use of broadcast and unicast):

If the client receives no response to DHCP messages sent 
to the IP address of a known DHCP server, the DHCP client 
reverts to using the IP broadcast address.

HTH

Rolf

[malshara]

I will try to check again ,and get back to you soon ,hope with an explanation :) .

thanks for your assistance