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] specifying dhcp options in proxy mode
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. If that reasoning is shown to be incorrect, it would be relatively simple to change the code to allow arbitrary options. Cheers, Simon. signature.asc Description: OpenPGP digital signature ___ 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 05/25/2017 01:30 PM, Simon Kelley wrote: On 23/05/17 13:09, Floris Bos wrote: On 05/11/2017 01:36 PM, Simon Kelley wrote: 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. Recall some operating systems like FreeBSD do not do DHCP again when net booting, but obtain the cached packet from PXE using the GET_CACHED_INFO PXE call. 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? Can specify which packet you want to have. From the PXE spec: == Op-Code: PXENV_GET_CACHED_INFO (0071h) Description: This service returns one of three buffers: 1. The client’s DHCPDISCOVER packet 2. The DHCP server’s DHCPACK packet 3. The Boot Server’s Discover Reply packet, which contains Option #60 set to “PXEClient”, a valid boot file name, and may contain MTFTP options == Recall FreeBSD asks for 3. So yes, I think that in theory it should work if the proxy DHCP packet contains the NFS root-path. The TS did not specify which operating system he is using though. So don't know if it also works with his. Yours sincerely, Floris Bos ___ 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 23/05/17 13:09, Floris Bos wrote: > On 05/11/2017 01:36 PM, Simon Kelley wrote: >> 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. > > Recall some operating systems like FreeBSD do not do DHCP again when net > booting, but obtain the cached packet from PXE using the GET_CACHED_INFO > PXE call. > > > Yours sincerely, > > Floris Bos > > 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? Cheers, Simon. > ___ > Dnsmasq-discuss mailing list > Dnsmasq-discuss@lists.thekelleys.org.uk > http://lists.thekelleys.org.uk/mailman/listinfo/dnsmasq-discuss > signature.asc Description: OpenPGP digital signature ___ 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 05/11/2017 01:36 PM, Simon Kelley wrote: 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. Recall some operating systems like FreeBSD do not do DHCP again when net booting, but obtain the cached packet from PXE using the GET_CACHED_INFO PXE call. Yours sincerely, Floris Bos ___ 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 12/05/17 15:35, Andriy Gapon wrote: > 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. > 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. Cheers, Simon. ___ 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 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
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. Cheers, Simon. On 10/05/17 14:32, Andriy Gapon wrote: > > It seems that present dnsmasq adds only vendor-specific option when it > operates > on the proxy mode. > E.g., with a config that has > dhcp-range=192.168.0.88,proxy,255.255.255.0 > dhcp-option=vendor:PXEClient,6,2b > dnsmasq adds option 43, suboption 6 to its responses. > > But if I have > dhcp-range=192.168.0.88,proxy,255.255.255.0 > dhcp-option=option:root-path,"192.168.0.200:/export/netboot" > then the root-path option is not set in the responses. > That's the case even if I use dhcp-option-force. > > Is there any reason for this? > Could dnsmasq be changed to allow explicitly set options for proxy responses? > I think that that would add more flexibility for users who know what they are > doing. > > P.S. > I found this old conversation: > http://lists.thekelleys.org.uk/pipermail/dnsmasq-discuss/2012q2/005722.html > Looks like the situation hasn't changed since then. > signature.asc Description: OpenPGP digital signature ___ Dnsmasq-discuss mailing list Dnsmasq-discuss@lists.thekelleys.org.uk http://lists.thekelleys.org.uk/mailman/listinfo/dnsmasq-discuss
