TFTP load balancing

Problem this snippet solves:

TFTP works in similar fashion to active FTP, using a callback from a random high port for the data stream: 1. The initiating host A sends a request packet to host B at Well Known Port 69. 1. B replies with a packet sent from an ephemeral port, which should be used for the remainder of the request for all data packets between Host A and host B.

To support the callback connection, you would: 1. Configure the UDP virtual server on port 69 to accept the control connection 1. Configure & apply a SNAT enabled at least on the server-side VLAN 1. Apply the following iRule to establish for each data connection a temporary listen on the appropriate port of the SNAT address.

Note: Requires LTM version > v9.0.3

How to use this snippet:

• Timeout should match the timeout in the UDP profile applied to the virtual server.
• Works with or without SNAT.

It is important to note that the LTM has to have a route back to the client since the new listener that is brought up to handle the data flow back to the client will not have an associate last-hop value.

Beware : because of simultaneous access by tftp client, the following error appears : TCL error: P_TFTP_NAT_IRULE - command returned bad code: 12

Code :

rule tftp_rule {
  when SERVER_CONNECTED {
    listen {
      proto 17
      timeout 60
      bind [LINK::vlan_id] [IP::local_addr] [serverside {UDP::local_port}]
      server [peer {client_addr}] [peer {UDP::client_port}]
      allow [IP::server_addr]
    }
  }
}