A hopefully easy to answer question, about multiple dhcp servers in 1 network. I'm looking into a thin client server (TCS) setup. As the TCS boots the clients using dhcp, I need to introduce a dhcpserver in an existing network. This shouldn't be a problem a guess, if the correct rules are followed.... But what are the correct rules ;) Is a dhcp server connected to a NIC (and therefor 1 physically lan) or does 1 dhcpserver serve multiple lan's or does it depend on the configuration? If the thin client server would have 2 NICs A and B, and nic A hosts the dhcpserver will the lan connected to B 'see' the dhcpserver attached to A? Followup questions: With the setup as described above: if lan B would have its own dhcpserver on e.g. server C is that possible without problem (of course the ip addresses should be defined correctly in the dhcpservers). Could the thin client server have 2 dhcp servers 1 serving lan A and the other serving lan B?? Just curious; is it possible to configure multiple dhcp servers with yast? From the dhcp tab it seems possible as one can select the ethernet card by mac number...., but I have never tried it. -- Richard Bos Without a home the journey is endless
Richard Bos wrote:
If the thin client server would have 2 NICs A and B, and nic A hosts the dhcpserver will the lan connected to B 'see' the dhcpserver attached to A?
If they are not connected in any other way and no routing is defined: no.
Followup questions: With the setup as described above: if lan B would have its own dhcpserver on e.g. server C is that possible without problem (of course the ip addresses should be defined correctly in the dhcpservers).
Could the thin client server have 2 dhcp servers 1 serving lan A and the other serving lan B?? Just curious; is it possible to configure multiple dhcp servers with yast? From the dhcp tab it seems possible as one can select the ethernet card by mac number...., but I have never tried it.
TCS would not need multiple dhcp servers. Only one is needed with several subnet ranges. Each of the ranges need to listen to a different ip address, so each lan will have its own address range. Options can be global or limited to one range. I never tried setting it up by yast, I simply used vi and man. (^-^). Sandy
Richard Bos wrote:
A hopefully easy to answer question, about multiple dhcp servers in 1 network. I'm looking into a thin client server (TCS) setup. As the TCS boots the clients using dhcp, I need to introduce a dhcpserver in an existing network. This shouldn't be a problem a guess, if the correct rules are followed....
If this existing network already has a DHCP server, you would simply amend that config.
Is a dhcp server connected to a NIC (and therefor 1 physically lan) or does 1 dhcpserver serve multiple lan's or does it depend on the configuration?
A DHCP server can serve whichever networks it is connected to. If the server has 16 NICs connecting to 16 networks, the DHCP server can serve all of them. If you use dhcprelay you can also serve networks to which the DHCP machine has no direct conenction.
If the thin client server would have 2 NICs A and B, and nic A hosts the dhcpserver will the lan connected to B 'see' the dhcpserver attached to A?
If I've understood your question, no. If you setup the DHCP server to only listen on eth0 (=NIC A), only machines on that network will be able to talk (directly) to that DHCP server.
Could the thin client server have 2 dhcp servers 1 serving lan A and the other serving lan B??
I think it's possible, but it makes little sense. You'd have to tweak the SuSE setup quite a bit - but why not just have one DHCP server serving both netweorks? /Per Jessen, Zürich -- http://www.spamchek.com/freetrial - sign up for your free 30-day trial now!
Sandy and Per, thanks for your replies. I got some more insight :) Op zaterdag 15 januari 2005 11:32, schreef Per Jessen:
A hopefully easy to answer question, about multiple dhcp servers in 1 network. I'm looking into a thin client server (TCS) setup. As the TCS boots the clients using dhcp, I need to introduce a dhcpserver in an existing network. This shouldn't be a problem a guess, if the correct rules are followed....
If this existing network already has a DHCP server, you would simply amend that config.
I don't know if I can change the config, and actually I don't want to change it. Anyway it is running that other OS.... -- Richard Bos Without a home the journey is endless
On Saturday 15 January 2005 04:50 am, Richard Bos wrote:
Sandy and Per,
thanks for your replies. I got some more insight :)
Op zaterdag 15 januari 2005 11:32, schreef Per Jessen:
A hopefully easy to answer question, about multiple dhcp servers in 1 network. I'm looking into a thin client server (TCS) setup. As the TCS boots the clients using dhcp, I need to introduce a dhcpserver in an existing network. This shouldn't be a problem a guess, if the correct rules are followed....
If this existing network already has a DHCP server, you would simply amend that config.
I don't know if I can change the config, and actually I don't want to change it. Anyway it is running that other OS....
--
Let's see if I understand what you want. You don't want to (or can't) change the config on the dhcp server servering the (main) network, but you want to set up some thin clients and they need to be served in a special way by a dhcp server. I *think*, you can do that. I haven't tried it. In my dhcp server, I set each thin client up in a separate host section. I serve my thin clients by mac address and use static ip addresses for them (and sometimes some host specific options). I also serve the 'regular' network clients with this dhcp server in a subnet section. If I pulled that subnet section out, I *think* it would no longer serve the regular network but would serve the individual hosts that were defined. Maybe someone with more dhcp knowledge could answer that for sure. Doug
On Sat, 15 Jan, 2005 at 08:45:14 -0600, Doug B wrote:
On Saturday 15 January 2005 04:50 am, Richard Bos wrote:
<snip>
I don't know if I can change the config, and actually I don't want to change it. Anyway it is running that other OS....
Hmmm... Does anything prevent you from ditching the present dhcp server? I think having more than one dhcp-server in a network is asking for trouble. And if the one already running doesn't provide you with the options you want... well I'd recommend swithing to one that will. AFAICT your options are basically: a) physically separate the existing network from the thin client network, and run separate dhcp-servers on each. b) set up *one* dhcp server to serve all clients in both networks via two interfaces. c) set up one dhcp server to serve all client (thin ones and regular alike) in one single network. For b) and c) you could certainly use the one included in the distro.
I *think*, you can do that. I haven't tried it. In my dhcp server, I set each thin client up in a separate host section. I serve my thin clients by mac address and use static ip addresses for them (and sometimes some host specific options). I also serve the 'regular' network clients with this dhcp server in a subnet section. If I pulled that subnet section out, I *think* it would no longer serve the regular network but would serve the individual hosts that were defined. Maybe someone with more dhcp knowledge could answer that for sure.
But the 'regular' dhcp server would probably still try to serve the thin clients... CMIIW /Jon -- YMMV
On Saturday 15 January 2005 11:42 am, Jon Clausen wrote:
AFAICT your options are basically:
a) physically separate the existing network from the thin client network, and run separate dhcp-servers on each.
I *think*, you can do that. I haven't tried it. In my dhcp server, I set each thin client up in a separate host section. I serve my thin clients by mac address and use static ip addresses for them (and sometimes some host specific options). I also serve the 'regular' network clients with this dhcp server in a subnet section. If I pulled that subnet section out, I *think* it would no longer serve the regular network but would serve the individual hosts that were defined. Maybe someone with more dhcp knowledge could answer that for sure.
But the 'regular' dhcp server would probably still try to serve the thin clients...
I think option a) is indeed the fact. IIRC the 'new' dhcp server had two nics. One to the 'reg' network and one to the 'thin' network. If the thin clients are on their own switch along with the 'thin' nic on the 'new' dhcp server then I think it should work with little or no chance of one dhcp server interfering with the other. By deleteing the subnet section of the 'new' dhcp server you eliminate (I think) the possibility of interfering with the 'reg' network dhcp server even should you accidently configure it to respond on both nics. I can see a scenerio where that would be needed. I have the pull to try some things at work, as long as I don't bother the IT folks for help. There is resistance to anything linux. I could get permission to do a thin net but I wouldn't be able to change/or have changed anything on the company dhcp server. I would have to set it up as described. The dhcp server for the thin clients would also be the boot server and server that hosts the thin clients. Since that server is actually running the programs being used, it would need to be tied to the company network in order for the thin clients to be able to do anything useful at work. Thus, a dhcp server on a machine that is on a lan servered by another dhcp server. Sometimes we don't get to play in a world where we can do things as they *should* be done. Doug
Op zaterdag 15 januari 2005 19:27, schreef Doug B:
I can see a scenerio where that would be needed. I have the pull to try some things at work, as long as I don't bother the IT folks for help. There is resistance to anything linux. I could get permission to do a thin net but I wouldn't be able to change/or have changed anything on the company dhcp server. I would have to set it up as described. The dhcp server for the thin clients would also be the boot server and server that hosts the thin clients. Since that server is actually running the programs being used, it would need to be tied to the company network in order for the thin clients to be able to do anything useful at work. Thus, a dhcp server on a machine that is on a lan servered by another dhcp server. Sometimes we don't get to play in a world where we can do things as they *should* be done.
Doug, this is my story! The only word to change is 'company', make it 'school' and that is where I am :) I would like to move the computer class from MS to 'ltsp', but I want to touch the rest of the network untill ltsp has proven to work reliable, etc. Thanks you guys, I have a much better insight in the dhcp technology now. -- Richard Bos Without a home the journey is endless
On Sat, 2005-01-15 at 09:45, Doug B wrote:
On Saturday 15 January 2005 04:50 am, Richard Bos wrote: Let's see if I understand what you want. You don't want to (or can't) change the config on the dhcp server servering the (main) network, but you want to set up some thin clients and they need to be served in a special way by a dhcp server.
I *think*, you can do that. I haven't tried it. In my dhcp server, I set each thin client up in a separate host section. I serve my thin clients by mac address and use static ip addresses for them (and sometimes some host specific options). I also serve the 'regular' network clients with this dhcp server in a subnet section. If I pulled that subnet section out, I *think* it would no longer serve the regular network but would serve the individual hosts that were defined. Maybe someone with more dhcp knowledge could answer that for sure.
Doug
The DHCP server that will answer requests is the one that is authoritative for the subnet and is the fastest to respond. Where I used to work there were two DHCP servers. One for the local LAN and one that was used for the WAN. I don't see a viable way to have two local servers unless one had restrictions based on the MAC address otherwise they would be fighting with each other to hand out addresses and you would end up with duplicate addresses. You might be able to use different ranges of addresses on two servers using one for resolution based on MAC address and the other would have to restrict the same MAC addresses. The only sure way is find out is through trial and error. -- Ken Schneider UNIX since 1989 SuSE since 1998 * Only reply to the list please*
Hi, a few remarks from my side, inline. On Sat, Jan 15, 2005 at 11:32:56AM +0100, Per Jessen wrote:
Richard Bos wrote:
Is a dhcp server connected to a NIC (and therefor 1 physically lan) or does 1 dhcpserver serve multiple lan's or does it depend on the configuration?
A DHCP server can serve whichever networks it is connected to. If the server has 16 NICs connecting to 16 networks, the DHCP server can serve all of them. If you use dhcprelay you can also serve networks to which the DHCP machine has no direct conenction.
Moreover, a DHCP server can serve many more networks, even if it is not directly attached to them (physically on the segment). Multiple DHCP relays (gateways relaying the DHCP protocol) can be between the server and clients (which are on a remote network). In addition, even though it is not relevant in this context, but just to mention it, the "physically attached network segments" served can be run over one single NIC, iv 802.1q (vlan) tagging is used to seperate them. DHCP is designed in a way that a single DHCP server's configuration can reflect the entire (complex) network structure. Administrating the network from one central point is especially interesting if networks are located far away from each other, like in different buildings, naturally.
Could the thin client server have 2 dhcp servers 1 serving lan A and the other serving lan B??
I think it's possible, but it makes little sense. You'd have to tweak the SuSE setup quite a bit - but why not just have one DHCP server serving both netweorks?
Two DHCP servers on one machine -- no, that is not possible, due to the way that dhcpd binds to the interfaces. However, it is not needed either. You would adapt /etc/sysconfig/dhcpd:DHCPD_INTERFACE and you would use the directive "authoritative" where appropriate. You would also declare subnets that are not served by dhcpd as empty subnets, and put multiple subnets that are using the same physical segment together into a "shared-network" statement, to tell the dhcpd about the real topology of the network. Peter
participants (7)
-
Doug B -
Jon Clausen -
Ken Schneider -
Per Jessen -
poeml＠cmdline.net -
Richard Bos -
Sandy Drobic