IPAddress Reservation (Best Practice)

[Luis Fernando Lacayo]

Thank for the quick response...

You are correct, I meant "Fixed address assignments"... That is what I
get from hanging around windows people. 


Please see my comments/questions below.
On Mon, 2008-08-11 at 13:57 +0100, Simon Hobson wrote:

> Luis Fernando Lacayo wrote:
> 
> >I have a quick question,  I have a bunch of subnets and I have DHCP 
> >Lease reservations for almost every network.
> 
> First off, I assume you mean "fixed address assignments" - lease 
> reservations are a bit of Windows terminology, different method of 
> working and plenty of scope for confusion !
> 
> >   my question is about how to define these reservations.  currently 
> >I have each reservation under its own subnet.  I have seen some 
> >configuration files that just bundles them at the end of the file. 
> >I imagine that this works.
> 
> They MUST NOT be within a subnet declaration. With a few exceptions 
> for some rather unusual requirements, you REALLY do not want them in 
> your subnet declarations. Host statements are global in scope (and so 
> are still 'valid' when the client is not in that subnet - BUT, 
> clients matching a host statement will inherit some options from the 
> subnet where the host declaration is made.
> 

OK, I think I understand.  Will this apply to the failover configuration
as well?  

So this setup would be incorrect:

## Third Floor South Wired
subnet 10.129.76.0 netmask 255.255.254.0 {
option routers 10.129.76.1;
...
option broadcast-address 10.129.77.255;
option domain-name-servers 10.129.161.20, 10.128.5.28;
option subnet-mask 255.255.254.0;
......
pool {
failover peer "co-wan03";
deny dynamic bootp clients;
allow unknown-clients;
range 10.129.76.21 10.129.76.230;
range 10.129.77.21 10.129.77.230;
}

## Anthony James
host Host-10.129.76.225 {
hardware ethernet 00:0d:56:a0:67:c4;
fixed-address 10.129.76.225;
}
}

## Fourth Floor Wired

subnet 10.129.78.0 netmask 255.255.254.0 {
option routers 10.129.78.1;
...
option broadcast-address 10.129.79.255;
option domain-name-servers 10.129.161.20, 10.128.5.28;
option subnet-mask 255.255.254.0;
....
pool {
failover peer "co-wan03";
deny dynamic bootp clients;
allow unknown-clients;
range 10.129.78.21 10.129.78.230;
range 10.129.79.21 10.129.79.230;
}

host Host-10.129.78.232 {
hardware ethernet 00:20:6b:51:db:45;
fixed-address 10.129.78.232;
}


It should be:

## Third Floor South Wired
subnet 10.129.76.0 netmask 255.255.254.0 {
option routers 10.129.76.1;
...
option broadcast-address 10.129.77.255;
option domain-name-servers 10.129.161.20, 10.128.5.28;
option subnet-mask 255.255.254.0;
......
pool {
failover peer "co-wan03";
deny dynamic bootp clients;
allow unknown-clients;
range 10.129.76.21 10.129.76.230;
range 10.129.77.21 10.129.77.230;
}


}

## Fourth Floor Wired

subnet 10.129.78.0 netmask 255.255.254.0 {
option routers 10.129.78.1;
...
option broadcast-address 10.129.79.255;
option domain-name-servers 10.129.161.20, 10.128.5.28;
option subnet-mask 255.255.254.0;
....
pool {
failover peer "co-wan03";
deny dynamic bootp clients;
allow unknown-clients;
range 10.129.78.21 10.129.78.230;
range 10.129.79.21 10.129.79.230;
}
}


## Anthony James
host Host-10.129.76.225 {
hardware ethernet 00:0d:56:a0:67:c4;
fixed-address 10.129.76.225;
}

## James Brown
host Host-10.129.78.232 {
hardware ethernet 00:20:6b:51:db:45;
fixed-address 10.129.78.232;
}





> In case you haven't worked that out, you can have a client getting a 
> dynamic IP address in one subnet, while inheriting the (incorrect) 
> router address from the subnet where it's host statement is declared. 
> I think anyone can imagine the confusion that could cause !


I have not ran into this issue yet.  but it could create 

> 
> >I am working on a small interface to to manage these because they 
> >are getting out of control, with staff members moving floors and 
> >printers being removed or relocated... 
> >
> >How are you defining your reservations? and better yet how are you 
> >managing them?
> 
> Many people store the information in a database (it can be anything 
> you are comfortable with), and then have a routine that will extract 
> the data and build a config file. You only need to build parts of a 
> file - for example you can just build a file with host declarations 
> and use the 'include" statement to include it in the main config file.
> 


Any special program (Open source) that you recommend?

Thanks again, 

Luis
-- 
Luis Fernando Lacayo
Chicago Public Schools
Senior Unix Administrator
ITS/ UNIX Infrastructure
Office: 773-553-3835
Cell: 773-203-4493
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