[syslinux] pxelinux tries to load ldlinux.c32 from DHCP server, instead of next-server

[Teun Docter]

Hello list,

We have a scenario where our TFTP server is not the same IP as our DHCP 
server. While testing with 6.03, our setup works just fine.

However with the master branch, for some reason pxelinux.0 is fetched 
from the TFTP servers IP, but then it tries to load ldlinux.c32 from the 
DHCP servers IP.

I've tracked down this problem to the following commit:

8e53b8a63c8ae1e266f63f502a537b9e8e03baed core/pxe: Don't prevent 
serverip override

If I reverse that change on the current master everything is working 
fine. This was with tested against 26d37f75aff50879795692728dbeb8ca57a8a226.

We're not using uefi for this test. (The machine is actually a KVM 
instance in OpenStack.)

I've captured the following DHCP ACK:

10.141.20.1.bootps > 10.141.20.2.bootpc: [udp sum ok] BOOTP/DHCP, Reply, 
length 399, xid 0xf0eb955a, secs 14, Flags [none] (0x0000)
           Your-IP 10.141.20.2
           Server-IP 10.141.255.254
           Client-Ethernet-Address fa:16:3e:08:31:b9
           Vendor-rfc1048 Extensions
             Magic Cookie 0x63825363
             DHCP-Message Option 53, length 1: ACK
             Server-ID Option 54, length 4: 10.141.20.1
             Lease-Time Option 51, length 4: 86400
             RN Option 58, length 4: 43200
             RB Option 59, length 4: 75600
             TFTP Option 66, length 7: "master^@"
             BF Option 67, length 11: "pxelinux.0^@"
             Subnet-Mask Option 1, length 4: 255.255.0.0
             BR Option 28, length 4: 10.141.255.255
             Domain-Name-Server Option 6, length 4: 10.141.20.1
             Domain-Name Option 15, length 14: "openstacklocal"
             Hostname Option 12, length 16: "host-10-141-20-2"
             Default-Gateway Option 3, length 4: 10.141.255.250
             T209 Option 209, length 45: 
112.120.101.108.105.110.117.120.46.99.102.103.47.99.97.116.101.103.111.114.121.46.118.105.114.116.117.97.108.45.110.111.100.101.115.46.111.112.101.110.115.116.
97.99.107
             MTU Option 26, length 2: 1450
             END Option 255, length 0

Followed by this TFTP request:

10.141.20.2.49152 > 10.141.20.1.tftp: [udp sum ok]  41 RRQ "ldlinux.c32" 
octet tsize 0 blksize 1408

It should be sending that TFTP request to 10.141.255.254.

So now I'm wondering, could this be a bug? Or should we change something 
in our DHCP settings? Is any further info required?

As a side note, could this be related to the recent thread with the 
following subject: "BUG: confusion between next-server and gateway"?
(http://www.syslinux.org/archives/2015-September/024090.html)

Best regards,
Teun