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f5gurunot's avatar
f5gurunot
Icon for Cirrus rankCirrus
Feb 02, 2023

TCP Option 28 X-Forwarded-For Header

Using Akamai for DDOS mitigation and the requests sent to us show Akamai IP instead of the Client IP.  I have enabled TCP Option 28 and trying to insert the Client IP into X-Forwarded-For header.  I ...
application delivery
  • xuwen's avatar
    xuwen
    Feb 03, 2023

    when CLIENT_DATA {
    set opt28 [TCP::option get 28]
    if { [string length $opt28] == 4 } {
    binary scan $opt28 H8 addr
    scan $addr "%2x%2x%2x%2x" ip1 ip2 ip3 ip4
    set optaddr "$ip1.$ip2.$ip3.$ip4"
    log local0. "optaddr is $optaddr"
    log local0. "ip addr parse result is [IP::addr parse -ipv4 $opt28]"
    }
    }

f5gurunot's avatar
f5gurunot
Icon for Cirrus rankCirrus

Just ran the following and not getting connection reset anymore.

tmsh create ltm profile tcp tcp_opt tcp-options "{28 first}"

However, still not seeing the Client IP.

Also, tried changing the HTTP_REQUEST to:


when HTTP_REQUEST {
if {$proto} {
HTTP::header insert X-Forwarded-Proto https
}
else {
HTTP::header insert X-Forwarded-Proto http
}
if { [info exists optaddr] } {
HTTP::header insert X-Forwarded-For $optaddr
}
}

xuwen's avatar
xuwen
Icon for Cumulonimbus rankCumulonimbus
Feb 03, 2023

can you insert a code below "set opt28 [TCP::option get 28]"

log local0. "tcp option 28 length is [string length $opt28]"

 and show the log give me, tail -f /var/log/ltm

  • f5gurunot's avatar
    f5gurunot
    Icon for Cirrus rankCirrus
    Feb 03, 2023

    Feb  2 19:58:26 bigip01.web.test.com info tmm3[12700]: Rule /Common/Akamai_Opt28 <CLIENT_ACCEPTED>: tcp option 28 length is 0

    • xuwen's avatar
      xuwen
      Icon for Cumulonimbus rankCumulonimbus
      Feb 03, 2023

      https://clouddocs.f5.com/api/irules/TCP__option.html

      tcp option 28 length is 0, It indicates that Akamai did not send the message with option 28 to F5，so below irules can not exec

       

       

      if { [string length $opt28] == 5 } {
binary scan $opt28 c ver

if { $ver != 1 } {
log local0. "Unsupported Akamai version: $ver"

} else {
set optaddr [IP::addr parse -ipv4 $opt28 1]
}
}

       

       

      cause variable optaddr is non-existent, so The action code that causes the insertion of XFF will not be executed

       

       

      if { [info exists optaddr] } {
HTTP::header insert X-Forwarded-For $optaddr
}

       

       

       

      • f5gurunot's avatar
        f5gurunot
        Icon for Cirrus rankCirrus
        Feb 03, 2023

        Thanks, appreciate your help!  That's what I was thinking as soon as I saw that.  Will see what Akamai says.