Hi Bob,
Thanks for your kind reply. I have tried your instructions. My system is Debian-amd64 sarge 3.1, so my configurations is more or less a little different from that in Redhat. My tftpd is configured in /etc/inetd.conf. There is a line is this file looks like
tftp dgram udp wait root /usr/sbin/tcpd /usr/sbin/in.tftpd /tftpboot
There are only my host and target board in my local net.
After I typed #tcpdump -i eth1, the messages are following,
# tcpdump -i eth1 tcpdump: verbose output suppressed, use -v or -vv for full protocol decode listening on eth1, link-type EN10MB (Ethernet), capture size 96 bytes 18:11:30.010752 arp who-has omap1.Nankai.edu.cn tell 192.168.4.190 18:11:30.012669 arp reply omap1.Nankai.edu.cn is-at 00:e0:4c:df:3d:48 18:11:30.011040 IP 192.168.4.190.2805 > omap1.Nankai.edu.cn.tftp: 39 RRQ "/tftpboot/u-boot.bin" octet timeout 5 18:11:30.012061 IP 192.168.0.11.33311 > 192.168.4.190.2805: UDP, length: 12 18:11:30.012359 IP 192.168.4.190.2805 > omap1.Nankai.edu.cn.33311: UDP, length: 4 18:11:30.012382 IP omap1.Nankai.edu.cn > 192.168.4.190: icmp 40: omap1.Nankai.edu.cn udp port 33311 unreachable 18:11:30.635567 IP 192.168.4.190.2805 > omap1.Nankai.edu.cn.33311: UDP, length: 4 18:11:30.635607 IP omap1.Nankai.edu.cn > 192.168.4.190: icmp 40: omap1.Nankai.edu.cn udp port 33311 unreachable 18:11:31.260528 IP 192.168.4.190.2805 > omap1.Nankai.edu.cn.33311: UDP, length: 4 18:11:31.260567 IP omap1.Nankai.edu.cn > 192.168.4.190: icmp 40: omap1.Nankai.edu.cn udp port 33311 unreachable 18:11:31.885490 IP 192.168.4.190.2805 > omap1.Nankai.edu.cn.33311: UDP, length: 4 18:11:31.885529 IP omap1.Nankai.edu.cn > 192.168.4.190: icmp 40: omap1.Nankai.edu.cn udp port 33311 unreachable 18:11:32.510452 IP 192.168.4.190.2805 > omap1.Nankai.edu.cn.33311: UDP, length: 4 18:11:32.510492 IP omap1.Nankai.edu.cn > 192.168.4.190: icmp 40: omap1.Nankai.edu.cn udp port 33311 unreachable 18:11:33.135414 IP 192.168.4.190.2805 > omap1.Nankai.edu.cn.33311: UDP, length: 4 18:11:33.135454 IP omap1.Nankai.edu.cn > 192.168.4.190: icmp 40: omap1.Nankai.edu.cn udp port 33311 unreachable 18:11:33.226036 IP 192.168.0.11.33304 > 192.168.4.190.2248: UDP, length: 12 18:11:33.760376 IP 192.168.4.190.2805 > omap1.Nankai.edu.cn.33311: UDP, length: 4 18:11:33.760416 IP omap1.Nankai.edu.cn > 192.168.4.190: icmp 40: omap1.Nankai.edu.cn udp port 33311 unreachable 18:11:34.385347 IP 192.168.4.190.2805 > omap1.Nankai.edu.cn.33311: UDP, length: 4 18:11:34.385388 IP omap1.Nankai.edu.cn > 192.168.4.190: icmp 40: omap1.Nankai.edu.cn udp port 33311 unreachable 18:11:35.010310 IP 192.168.4.190.2805 > omap1.Nankai.edu.cn.33311: UDP, length: 4 18:11:35.010349 IP omap1.Nankai.edu.cn > 192.168.4.190: icmp 40: omap1.Nankai.edu.cn udp port 33311 unreachable 18:11:35.010732 arp who-has 192.168.4.190 tell omap1.Nankai.edu.cn 18:11:35.010891 IP 192.168.0.11.33311 > 192.168.4.190.2805: UDP, length: 12 18:11:35.011042 arp reply 192.168.4.190 is-at 00:0e:99:02:0a:21 18:11:35.011254 IP 192.168.4.190.2805 > omap1.Nankai.edu.cn.33311: UDP, length: 4 18:11:35.011268 IP omap1.Nankai.edu.cn > 192.168.4.190: icmp 40: omap1.Nankai.edu.cn udp port 33311 unreachable 18:11:35.635276 IP 192.168.4.190.2805 > omap1.Nankai.edu.cn.33311: UDP, length: 4 18:11:35.635314 IP omap1.Nankai.edu.cn > 192.168.4.190: icmp 40: omap1.Nankai.edu.cn udp port 33311 unreachable 18:11:36.260237 IP 192.168.4.190.2805 > omap1.Nankai.edu.cn.33311: UDP, length: 4 18:11:36.260275 IP omap1.Nankai.edu.cn > 192.168.4.190: icmp 40: omap1.Nankai.edu.cn udp port 33311 unreachable 18:11:38.152001 arp who-has omap1.Nankai.edu.cn tell 192.168.4.190
............
omap1.Nankai.edu.cn is my hostname, 192.168.0.11 is the IP of eth0 witch is connected to external LAN. If the message above shows that my client setup is correct? I am wondering about why the UDP packets were sent to 192.168.0.11 rather than 192.168.4.1? Is it the problem?