TFTP timeout problem during PXE boot

While setting up a PXE boot server on a CentOS 7 machine, I encountered a strange problem with TFTP. I cannot retrieve any files from the TFTP server without encountering a timeout problem. The boot process comes so far that I correctly get an IP address and a file name from the DHCP server. However, when the boot files are to be retrieved from the TFTP server, a "TFTP open timeout" message comes. If I manually make a TFTP connection to the PXE server from a local computer, I immediately get access to the server. But if I try with a "get pxelinux.0" command, I get another timeout message. My firewall is set up correctly and it also makes no difference if I completely turn off the firewall. SeLinux is also disabled. If I make a tcpdump on port 69 I get the following message: 12:34:33.477401 IP 172.16.1.202.ah-esp-encap > tools.dmz.tuxme.dk.tftp: 27 RRQ "pxelinux.0" octet tsize 0 12:34:35.481131 IP 172.16.1.202.acp-port > tools.dmz.tuxme.dk.tftp: 27 RRQ "pxelinux.0" octet tsize 0 12:34:39.490793 IP 172.16.1.202.msync > tools.dmz.tuxme.dk.tftp: 27 RRQ "pxelinux.0" octet tsize 0 12:34:45.477712 IP 172.16.1.202.gxs-data-port > tools.dmz.tuxme.dk.tftp: 27 RRQ "pxelinux.0" octet tsize 0 12:34:53.441801 IP 172.16.1.202.vrtl-vmf-sa > tools.dmz.tuxme.dk.tftp: 27 RRQ "pxelinux.0" octet tsize 0 12:35:03.384065 IP 172.16.1.202.newlixengine > tools.dmz.tuxme.dk.tftp: 32 RRQ "pxelinux.0" octet blksize 1456 12:35:39.414843 IP 172.16.1.202.newlixconfig > tools.dmz.tuxme.dk.tftp: 32 RRQ "pxelinux.0" octet blksize 1456 12:36:51.422568 IP 172.16.1.202.tsrmagt > tools.dmz.tuxme.dk.tftp: 32 RRQ "pxelinux.0" octet blksize 1456 12:38:39.406732 IP 172.16.1.202.tpcsrvr > tools.dmz.tuxme.dk.tftp: 32 RRQ "pxelinux.0" octet blksize 1456 Unfortunately, the system log shows nothing useful: Jan 15 13:13:19 tools xinetd: EXIT: tftp status=67 pid=7954 duration=0(sec) Jan 15 13:13:21 tools xinetd: START: tftp pid=7955 from=172.16.1.202 Jan 15 13:13:21 tools in.tftpd: no user tftp: Success Jan 15 13:13:21 tools xinetd: EXIT: tftp status=67 pid=7955 duration=0(sec) Jan 15 13:13:25 tools xinetd: START: tftp pid=7956 from=172.16.1.202 Jan 15 13:13:25 tools in.tftpd: no user tftp: Success Jan 15 13:13:25 tools xinetd: EXIT: tftp status=67 pid=7956 duration=0(sec) Jan 15 13:13:31 tools xinetd: START: tftp pid=7957 from=172.16.1.202 Jan 15 13:13:31 tools in.tftpd: no user tftp: Success The rights to the /var/lib/tftpboot directory are 0755. Here are my setup file: /etc/xinetd.d/tftp: service tftp socket_type = dgram protocol = udp wait = yes user = root server = /usr/sbin/in.tftpd server_args = -c -v -u tftp -p -U 117 -s /var/lib/tftpboot disable = no per_source = 11 cps = 100 2 flags = IPv4