Re: [Dnsmasq-discuss] specifying dhcp options in proxy mode
On 11/05/2017 14:36, Simon Kelley wrote: > The design is that dnsmasq sends the options expected by a PXE client if > it's acting as a proxy (because the whole proxy thing is part of the PXE > spec: a normal DHCP client doesn't know how to deal with it.) The > replies to the PXE client are constructed using the information given in > the pxe-service and pxe-prompt options. The inclusion of arbitrary > vendor-specific options is an oversight, I think. > > As the PXE-spec doesn't AFAIK, include root-path as an expected option, > I'm not sure that sending it will have any effect. > > As stated in the thread you link to, if you're netbooting an OS via PXE > then one the OS starts, it will do DHCP again, and that's the time to > send arbitrary options. > > TL;DR I don't think implementing what you're asking for will achieve > what you want, but if you can demonstrate that it will, then I'll > certainly looking at adding the extra function. Simon, thank you very much for reply. My reason for wanting that feature is to support a scenario where is a main DHCP server that is tasked only with giving out network information and which I can not modify at all. In my opinion options like root-path, swap-server and similar belong to the same league as, say, bootfile-name rather than, say, dns-server or router. In either case, my main DHCP server is not configured to advertise root-path. Also, in my case it is the OS that wants to get root-path not the first stage PXE loader. So, without dnsmasq allowing me to send root-path option there is no way I can give it to the OS. I thought that the purpose of the proxy mode was exactly to help with PXE / OS booting in situations where the main DHCP server can not be altered to do that job. Having said all of the above, I should admit that the OS in question could be non-compliant with the PXE specification. Maybe it should use a different mechanism like vendor options or a configuration file (advertised via bootfile-name) to get the information it needs. -- Andriy Gapon ___ Dnsmasq-discuss mailing list Dnsmasq-discuss@lists.thekelleys.org.uk http://lists.thekelleys.org.uk/mailman/listinfo/dnsmasq-discuss
Re: [Dnsmasq-discuss] specifying dhcp options in proxy mode
On 23/05/2017 01:14, Simon Kelley wrote: > To the best of my knowledge it's _only_ PXE clients which can accept > extra options from a proxy. PXE is a superset of DHCP, which includes > that functionality. The DHCP clients run by the OS are just that - DHCP > clients, they don't know how to do the PXE proxy-server tricks. It seems that the discussion went into a direction that I didn't expect. Let me try to make it simpler (for me) again. So, should dnsmasq in the DHCP proxy mode be able to send a root-path option? -- Andriy Gapon ___ Dnsmasq-discuss mailing list Dnsmasq-discuss@lists.thekelleys.org.uk http://lists.thekelleys.org.uk/mailman/listinfo/dnsmasq-discuss
Re: [Dnsmasq-discuss] specifying dhcp options in proxy mode
On 25/05/2017 14:30, Simon Kelley wrote: > How does this handle the case that the PXE client has received _two_ > packets, one from the DHCP server with an IP address, and one from a PXE > proxy server with netbbot information. Does GET_CACHED_INFO return one, > or both, or the combined information from both? Here is my understanding of how x86 FreeBSD network boot works on a high level. First, the initial PXE client must be instructed to load and run FreeBSD pxeboot. pxeboot is a special loader, an intermediate stage that loads the actual FreeBSD kernel. pxeboot is itself a DHCP and PXE client. In a typical setup pxeboot uses NFS for access to its configuration files, the kernel and kernel modules. In that case pxeboot does want to get a root-path in an offer, that's where it gets an NFS share path. When pxeboot is ready to run the kernel, pxeboot passes the DHCP lease information and the NFS path information to the kernel, so that the kernel can properly configure its network interface and mount the root filesystem over NFS. -- Andriy Gapon ___ Dnsmasq-discuss mailing list Dnsmasq-discuss@lists.thekelleys.org.uk http://lists.thekelleys.org.uk/mailman/listinfo/dnsmasq-discuss
Re: [Dnsmasq-discuss] specifying dhcp options in proxy mode
On 25/05/2017 14:29, Simon Kelley wrote: > > > On 23/05/17 07:05, Andriy Gapon wrote: >> On 23/05/2017 01:14, Simon Kelley wrote: >>> To the best of my knowledge it's _only_ PXE clients which can accept >>> extra options from a proxy. PXE is a superset of DHCP, which includes >>> that functionality. The DHCP clients run by the OS are just that - DHCP >>> clients, they don't know how to do the PXE proxy-server tricks. >> >> It seems that the discussion went into a direction that I didn't expect. >> >> Let me try to make it simpler (for me) again. >> So, should dnsmasq in the DHCP proxy mode be able to send a root-path option? >> > > No it can't. It's deliberate that it can't and the reasoning for that is > that packets sent in proxy mode can only go to a PXE client, which > doesn't know what to do with (eg) a root-path option. As an example, iPXE does know what to do with root-path in certain cases: http://ipxe.org/howto/dhcpd http://ipxe.org/sanuri As an aside, as far as I can see, iPXE never contacts the proxy server on the proxy port. It takes all information it needs from the proxy's DHCP offer packet and does not perform any further communication with it. > If that reasoning is shown to be incorrect, it would be relatively > simple to change the code to allow arbitrary options. > -- Andriy Gapon ___ Dnsmasq-discuss mailing list Dnsmasq-discuss@lists.thekelleys.org.uk http://lists.thekelleys.org.uk/mailman/listinfo/dnsmasq-discuss
Re: [Dnsmasq-discuss] proxy for pxe - intro
On 25/05/2017 20:16, Carl Karsten wrote: > Andriy's questions have me interested, maybe this will help when I want to pxe > boot a machine but don't have access to the dhcp server. > > like if I have 2 laptops B (proxy) and C (pxe client) both plugged into a lan > with dhcp server A and gateway G. I want C to get IP/subnet/gateway assigned > by > A, but also next-server/filename assigned by B. > > I am assuming there is some trick to tell C to only work with proxy B and > ignore > responses from A? > > can it be done with settings or do I need to physically (or switch config) > isolate C from A? > > feel free to point me at a doc that explains this I simple Google query for "dnsmasq pxe proxy" returns very useful results right at the top (at least, it does for me). E.g.: https://n0dy.com/blog/2014/09/14/network-booting-with-dnsmasq-in-proxy-mode/ https://wiki.fogproject.org/wiki/index.php?title=ProxyDHCP_with_dnsmasq https://manski.net/2016/09/pxe-server-on-existing-network-dhcp-proxy-on-ubuntu/ http://danielboca.blogspot.com/2012/02/boot-linux-from-network-using-pxe-and.html -- Andriy Gapon ___ Dnsmasq-discuss mailing list Dnsmasq-discuss@lists.thekelleys.org.uk http://lists.thekelleys.org.uk/mailman/listinfo/dnsmasq-discuss
