PXE boot port issue

Hi,all:
I want to boot an IA unix box from network, I am sure I set the DHCP and boot server, but it still failed !

It says : Client MAC Address: 00 18 FE 28 91 82 .....-
PXE-E16: Valid PXE offer not received.
Load of Core LAN Gb A failed: Not Found

I use the nettl command to trace the UDP package, it writes:

^^^^^^^^^^^^^^^^^^^^^^Gigabit Ethernet LAN/9000 Networking^^^^^^^^^^^^^^^^^^@#%
Timestamp : Fri Apr 27 EAT 2007 16:57:52.714302
Process ID : [ICS] Subsystem : IGELAN
User ID ( UID ) : -1 Trace Kind : PDU IN TRACE
Device ID : 0 Path ID : -1
Connection ID : 0
Location : 00123

=================================== Ethernet ====================================
Source : 00-18-fe-28-91-82  [i][                  ] 
Dest   : ff-ff-ff-ff-ff-ff  [b][                  ] TRACED LEN: 590
Date   : Fri Apr 27 16:57:52.714302 EAT 2007
================================ IP Header \(inbound -- [ICS]\) ================
Source:  0.0.0.0   \(A\) Dest:  255.255.255.255\(E\)
       len:  576     ttl: 16    proto: 17     cksum:  0xf3ee      id: 0xb4bf
     flags:  NONE    tos: 0x0  hdrlen: 20    offset:  0x0     optlen: 0   
-------------------------------- UDP Header \----------------------------------
sport:   68   -->   dport:  4109     data len: 548   chksum: 0x3c04 
-------------------------------- BOOTP Request \-------------------------------
trans id  : 0x13880000      seconds  : 159             hops   : 0  
server  IP: NULL            client IP: NULL            your IP: NULL           
gateway IP: NULL            h/w type : 1               flags  : 32768          
client h/w addr : 00-18-fe-28-91-82
server name     : NULL
file name       : NULL
vendor specific : VM_RFC1048

From the document, I got that the client port is 68, the server port should be 67, I mean the DHCP server listening port, while in the UDP package, it shows 4109.
Thanks !