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As I understand, it is responsibility of the client to send renew requests periodically. How long is this period? Can I receive this information once IP address is dynamically assigned do my interface? Does DHCP protocol provides me this information or I should ask it from the server administrator?

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closed as off topic by Michael Hampton, Magellan, rnxrx, Ward, MadHatter Oct 15 '12 at 12:33

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Welcome to Server Fault, a site for IT professionals. We've tried to give you answers appropriate to system administrators, but your question now indicates that you are an end user. It will likely be closed for this reason. If you are interested in learning what your DHCP lease time is, you may wish to visit our sister site Super User. Before posting there (or here!) you should check the FAQ to learn what is on topic, and search to see if your question has been asked before. You should also clarify the question to specify your operating system, etc. –  Michael Hampton Oct 14 '12 at 19:43
    
I do not understand why you deleted my comment where I explain that my question is not appropriate in Superuser. Superuser explicitly says that it is not intended for corporate networks. Secondly, we have nobody discovered duplicate of this question, so your blaming me that I did not do the search is inappropirate also. So, we have inappropriate and inadequate administration in the Serverfault. –  Val Oct 14 '12 at 21:53
    
@Val The comment was deleted due to combative tone, much like you're showing in your new comment. These are community run sites with not as much inter-site communication as any one would like. Inadequate administration is part and parcel to StackExchange, we just try to minimize it as much as possible. –  sysadmin1138 Oct 15 '12 at 1:59
    
There is nothing combative when person is wondering why he is sent to inappropriate forum. I used analogy with fruits (if I consume apples at home then you should discuss it at householding forum, you say, not our professional fruit forum). There is nothing combative in this analogy. Sending me into inappropriate discussion board, that is combative. –  Val Oct 15 '12 at 7:09
    
@Val: You don't appear to be a corporate network admin which puts you outside our scope too. This doesn't seem like a corporate network question either - it's a user level question about a corporate network as your edit reveals. meta.serverfault.com/a/3397/9517 is interesting in this regard. –  Iain Oct 15 '12 at 8:10

3 Answers 3

up vote 0 down vote accepted

The lease time is sent in a DHCP option.

Here, excerpt of tshark -V output:

Option: (t=51,l=4) IP Address Lease Time = 3 days
    Option: (51) IP Address Lease Time
    Length: 4
    Value: 0003F480

From dhcpoptions(5):

option dhcp-lease-time uint32;

This option is used in a client request (DHCPDISCOVER or DHCPREQUEST) to allow the client to request a lease time for the IP address. In a server reply (DHCPOFFER), a DHCP server uses this option to specify the lease time it is willing to offer.

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Thanks, I see, it matches the difference between Lease Obtained and Lease Expires in ipconfig /all. –  Val Oct 14 '12 at 21:34

The client will initially try and renew the lease from the DHCP server that supplied it when 50% of the lease time has expired. If it gets no response by the time 87.5% of the lease time has expired the client will try to obtain a new lease from any DHCP server that will respond.

If it gets a response then the timers are reset to 0 and restarted.

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To compute 0.5 and 0.87, I need to know what is 1! –  Val Oct 14 '12 at 19:09
    
@Val: the client knows this –  Iain Oct 14 '12 at 19:10
    
@Val: you need to tell us what your client is so we can tell you the rest. –  Iain Oct 14 '12 at 19:10
    
I use two clients: Microsoft Windows 7 (DHCP works fine) and lwIP (I need DHCP there) –  Val Oct 14 '12 at 19:15
    
@Val: windows 7 ipconfig/all will tell you under Lease Obtained and Lease Expires –  Iain Oct 14 '12 at 19:17

The validity period of the lease is however long you set it up to be on the DHCP server. Clients typically renew the lease once 50% of that time has elapsed, though actual DHCP client implementations may vary.

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can server tell me the period so that I can determine what is 50%? –  Val Oct 14 '12 at 19:07
    
Just look at the server's configuration. You didn't say what DHCP server you were running. –  Michael Hampton Oct 14 '12 at 19:08
    
I am asking whether I can receive that information over DHCP. –  Val Oct 14 '12 at 19:11
    
Yes, it's sent to your client, obviously. –  Michael Hampton Oct 14 '12 at 19:12

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