> From: Andrey Borzenkov [mailto:arvidj...@gmail.com] > Sent: Monday, April 21, 2014 7:36 PM > > В Tue, 22 Apr 2014 00:13:15 +0000 > "Mroczek, Joseph T" <joseph.t.mroc...@intel.com> пишет: > > > > From: Andrey Borzenkov [mailto:arvidj...@gmail.com] > > > Sent: Monday, April 21, 2014 10:42 AM > > > > > > В Mon, 21 Apr 2014 15:56:07 +0000 > > > "Mroczek, Joseph T" <joseph.t.mroc...@intel.com> пишет: > > > > > > > > > From: Behalf Of Vladimir 'f-coder/phcoder' Serbinenko On > > > > > 19.04.2014 02:48, Mroczek, Joseph T wrote: > > > > > > Hello: > > > > > > > > > > > > Currently, the DHCP logic assumes that if a gateway is > > > > > > received in the DHCP > > > > > packet the boot server is on a remote network. Given that CIDR > > > > > is now over > > > > > 20 years old, I think it is a safe assumption that a netmask > > > > > will be offered in DHCP options. > > > > > > > > > > > > Can this be removed? Or is there still a need to cover the classful > case? > > > > > > > > > > > Please detail the failure scenario. > > > > > Current code follows standard behaviour for PXE clients and > > > > > changing it would break any installation which relies on it. > > > > > > > > > > Hmm ... re-reading RFC2131 I ask myself what are conditions when > > > *client* is supposed to use gateway_ip at all. According to RFC, > > > giaddr is set by DHCP relay when it forwards request from client so > > > server knows where to send reply to. DHCP relay then forwards reply > > > on local subnet according to standard rules. RFC does not say anything > about client usage of this field. > > > Actually there is no requirement that DHCP relay also functions as > > > normal router. > > > > Use of giaddr as a gateway dates back to RFC951. At that point in time we > did not have DHCP options, so this was a way to dynamicially learn the > gateway. > > > > Oh. Digging further, RFC1542 quite explicitly states the same: > > A BOOTP client MUST NOT interpret the 'giaddr' field of a BOOTREPLY > message to be the IP address of an IP router. A BOOTP client SHOULD > completely ignore the contents of the 'giaddr' field in BOOTREPLY > messages. >
I saw this. I did not remove all of the use of giaddr field because of regression concerns. > > > > The failure will occur in most if not all cases where the DHCP > > > > sends a gateway when the boot server is on the same subnet as the > > > > client, > > > > > > In view of the above, how is it possible? DHCP server is not > > > supposed to set this field at all - at the most it simply replies > > > back to relay with same value of giaddr it got. If giaddr is set it > > > is already indication that server and client are on different subnets. > > > > For my case, DHCP server is on different subnet but boot/TFTP server is on > same as client. > > > > I see. I rather agree with your patch, it looks like semantic of giaddr was > settled 20 years ago. Great. Thanks! _______________________________________________ Grub-devel mailing list Grub-devel@gnu.org https://lists.gnu.org/mailman/listinfo/grub-devel
