related to leases...........need help plzz....

hitesh sharma hitesh at elitecore.com
Tue Feb 13 06:20:55 UTC 2007


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thanks ....................=0D
    some of my questions is unable to understand u , so now i will try to
explain u ........=0D
1> actually , i want to know about the fixed leases which is declared in
client's .conf  file , let suppose when there is no dhcp server , then
client will assign the fixed leases which one is declared in leases
statement , but i want to know , that what i will have to do , that clien=
t
will automatically detect the server when server comes into lan ? =0D
 =0D
2> in client's .conf file , when i declared fixed leases , i.e. inside
leases statement , then there is three fields  renew , rebind , and expir=
y .
 so what is  =0D
     significance  of them .=0D
3 >    we know that in client .conf  file , after  "timeout statement " ,
client will assign the fixed leases (when there is no valid leases in=20
leases file ) , but i want to know , once fixed leases allocated to clien=
t ,
then retry statement will execute ? =0D
   i am also copying , my chclient.conf  file , plz take a look of this .=
=2E..
=2E...............=0D
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send dhcp-lease-time 60;=0D
request subnet-mask, broadcast-address, time-offset, routers,=0D
        domain-name, domain-name-servers, host-name;=0D
require subnet-mask, domain-name-servers, routers;=0D
timeout 20;=0D
retry 30;   // i want to know about this statement=0D
reboot 10;=0D
select-timeout 5;=0D
initial-interval 2;=0D
script "/sbin/dhclient-script";=0D
#media "-link0 -link1 -link2", "link0 link1";=0D
#interface "eth0" {=0D
#                reject 192.168.0.76;=0D
#                send dhcp-lease-time 400;=0D
#               send dhcp-client-identifier 00:0C:29:B1:A6:32;=0D
#               }=0D
 =0D
#interface "eth1" {=0D
#               send dhcp-client-identifier 00:0C:29:B1:A6:3C;=0D
#                send dhcp-lease-time 600 ;=0D
#               }=0D
=0D
lease {=0D
  interface "eth0";=0D
  fixed-address 192.168.15.195;=0D
  medium "link0 link1";=0D
   option host-name "fixed add eth0";=0D
  option subnet-mask 255.255.240.0;=0D
  option broadcast-address 192.168.15.255;=0D
  option routers 192.168.15.195;=0D
  option domain-name-servers 192.168.15.195;=0D
 # renew 0 2007/2/3 00:00:01;  // i also want to know @  these three
statement=0D
 # rebind 0 2007/2/3 00:00:01;=0D
  expire 0 2007/2/3 00:00:01;=0D
}=0D
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lease {=0D
       interface "eth1";=0D
       fixed-address 192.168.15.197;=0D
     option host-name "fixed add eth1";=0D
       option subnet-mask 255.255.240.0;=0D
       option broadcast-address 192.168.15.255;=0D
       option routers 192.168.15.197;=0D
       option domain-name-servers 192.168.15.197;=0D
  #      renew 0 2007/2/3 00:00:01;=0D
   #     rebind 0 2007/2/3 00:00:01;=0D
         expire 0 2007/2/3 00:00:01;=0D
      }=0D
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   thanks ............................=0D
             waiting for ur reply......................................=0D
                                                                         =
  =20
          Hitesh Sharma=0D
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-------Original Message-------=0D
 =0D
From: dhcp-users at isc.org=0D
Date: 02/13/07 04:39:17=0D
To: dhcp-users at isc.org=0D
Subject: Re: related to leases...........need help plzz....=0D
 =0D
hitesh sharma wrote:=0D
 =0D
>actualiy , i want to know that ,=0D
>1>  when i am using fixed address (leases statement inside the .conf fil=
e),=0D
>then how to limit this address , i.e. if i want to use fixed address at=0D
>certain time?=0D
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Not sure what the question is. Are you asking for conditional=0D
allocation, eg "client X can have address a.b.c.d but only between=0D
9am and 5pm" ?=0D
 =0D
Firstly, I am not aware of any DHCP server offering any such=0D
function, and in any case it would be non trivial to implement - each=0D
time the client renews a lease you would have to compute the time the=0D
lease is to remain valid and offer a lease that does not exceed that=0D
time. Certainly a lot more work than "is the time within the=0D
specified time window".=0D
 =0D
Remember that DHCP is NOT a security protocol, it is trivial to=0D
bypass such restrictions by manually configuring a client. If you=0D
need to restrict use of systems, then there are generally better ways=0D
of doing it.=0D
 =0D
>2>  if , i want that , if my machine is using fixed address , but=0D
>when any server comes inro lan , it should detect that server , and=0D
>produce request for leases.=0D
 =0D
No, or at least not 'out of the box'. The server does not broadcast=0D
it's presence, it is up to the client to ask. Yes it would be=0D
possible to configure a system to repeatedly attempt to lease an=0D
address and switch between the dhcp lease and another statically=0D
configured address depending on whether you get a reply - but that=0D
defeats the object of dhcp which is to reduce or eliminate=0D
configuration of clients. What you are asking for would significantly=0D
increase the administrative burden of managing clients.=0D
 =0D
What many clients DO support is dynamically allocated "link local"=0D
addresses - ie they will attempt to obtain a lease by dhcp, but if=0D
they fail then they will allocate themselves an address in the=0D
reserved "link local" range. If a dhcp server comes onto the network,=0D
then (normally) these clients will get a lease because the client=0D
will keep broadcasting for a dhcp server every few minutes. This is=0D
entirely client specific and has no effect whatsoever on the dhcp=0D
server.=0D
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>  3>   In case of fixed address, the renew , expire and rebind statement=
 is=0D
>compulsory ? can i declare leases statement without that ? if not ,=0D
>then what is significance of them?=0D
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Can you clarify the question ?=0D
 =0D
In general, there are no mandatory configuration options for the=0D
client, and very few for the server.=0D
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>4>   i face one more problem , when i release the one of the leases=0D
>(eth0/eth1), by using  -r flag , then after sometime , it also take=0D
>the leases=0D
>from server. so , how to avoid leases , when one of the or both=0D
>interface don't want  leases , but even need to be in lan?=0D
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Sorry, I don't understand the question.=0D
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>6>    when i m releasing the lease , and i want message related to=0D
>that ie. message no. 7 , then , how to get it ?=0D
 =0D
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>7>    in  /var/lib/dhcp ,  in .leases file , it will comntain all leases=
,=0D
>or only those are valid ?=0D
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It may well contain older records as well.=0D
 =0D
>8>    we know that , at the 50 % time of  leases, client  try the=0D
>renew it if it successes in that , remaining   50%  leases first=0D
>will use by client then new allocated leases , or , client will use=0D
>new leases , n but remaining 50% leases in leases database.=0D
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Once a new lease is issued, the expiry time of the previous lease is=0D
irrelevant, the new expiry time is whatever the server offers in the=0D
new lease - this can be (if the configuration has changed) shorter=0D
than the previous one !=0D
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Eg, suppose lease time is set to 4 days, and client is started at 9am=0D
Monday, it will get a lease expiring at 9am Friday. Suppose=0D
administrator changes lease time to 1 day after this lease is issued,=0D
this will NOT affect the clients exiting lease. At 9am on Wednesday=0D
(after 2 days, 50% of the original lease time), the client will renew=0D
the lease, the server will offer it a 1 day lease, and if the client=0D
accepts it, it will now have a lease expiring at 9am Thursday.=0D
 =0D
If the config had not been changed, then the new lease would also be=0D
for 4 days and would expire 9am Sunday.=0D
 =0D
Bear in mind that the 50% time for attempting a renewal is only a=0D
default, and may also be client specific.=0D
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