Forum Discussion
serge_faller_83
Altostratus
AltostratusAdd a new data on the UDP payload
Hi,
I wish to find a way with an iRule to save a src_adress (client) at the end of the
UDP payload before SNAT. ( use RADIUS )
I implemented the irules according to :
. Update the end of payload with this adress : UDP::payload replace
-> failure
. Update UDP length and IP length, and chck=0 : ?
how can I replace length UDP, IP and checksum ( no IP::length, IP::chck)
thanks for the help
irules :
-------
set udp_size [UDP::payload length]
set size_IP 4
set Ip_src_adr [IP::client_addr]
update length and checksum
set [UDP::payload length] [ expr $size_IP + $size_IP ]
-> no update
save @IP
UDP::payload replace $udp_size $size_IP $Ip_src_adr
-> it doesn't work - failure
4 Replies
- The UDP::payload replace command will automatically update the datagram length and checksum. The command syntax is as follows:
UDP::payload replace
It's important to note that is the amount of data to replace. It is not the size of . For example, the following code snippet will insert the client IP address at the beginning of the datagram. The IP address will be inserted as a string. Perhaps you're attempting to insert the IP address as a 32 bit number?when CLIENT_DATA { UDP::payload replace 0 0 [IP::remote_addr] } - Just to add to Dr. Teeth's post. You problem is that:
A) You don't set the length using UDP::payload length. The length is automatically determined by the amount of payload.
B) You can't replace 4 bytes starting at the end of the payload. You can insert 4 bytes at the end by using:UDP::payload replace $udp_size 0 $Ip_src_adr
Also, if you do want to insert the IP address as a 32-bit (4 byte) number, you may want to search the forum for some examples of converting the IP address to a integer value. 
serge_faller_83thanks for your help,
Indeed I tried <>, it works ..
But I have always a problem with my adress format.
I don't find tcl solution to convert the ip_adress... (?)
. set "Ip_src_adr [IP::client_addr]" give : Ip_src_adr=155.132.226.3
. "binary scan [IP::client_addr] h* Ip_adr" give : Ip_adr=135353e2133323e2232363e233
...
Can I read client_addr on IPheader without using IP::client_addr to have a binary or hex format ?- You would likely need to use the regular scan and some math:
scan [IP::client_addr] "%u.%u.%u.%u" ip1 ip2 ip3 ip4 set ip [expr {(ip1 << 24) + (ip2 << 16) + (ip3 << 😎 + ip4}]
