Host Engineering Forum

General Category => Do-more CPUs and Do-more Designer Software => Topic started by: JeffS on July 22, 2021, 06:17:57 PM

Title: BRX Pings failing
Post by: JeffS on July 22, 2021, 06:17:57 PM

So in one of my projects, I use the PLC to manage the IP addresses of some connected VFDs.  In some of my logic 2 VFDs can have the same IP address, and I just disconnect one in order to sort it out.  The problem I am having is that I change the first VFD's address (.17.72) to something new(.19.5) and then when I plug in the second VFD that has the same IP as the one I just changed previously (.17.72) the ping I perform from the BRX fails.  I can ping this drive from other devices on the network just fine, but the BRX keeps failing.

If I power cycle the BRX it will ping the device (.17.72).  It will also find the device after sitting for 10-15 minutes.

Firmware 2.8.6
Booter 1.0.10
FPGA 1.15
Hardware 8A3A 

Title: Re: BRX Pings failing
Post by: BobO on July 23, 2021, 12:57:58 PM

Sounds almost like an ARP record is involved. Power cycling clears it, or after some time it ages out. I wouldn't have guessed ping would be affected by ARP, but maybe.

Not really sure what to do about it. Duplicating IP addresses is kinda on the edge to start with, and I routinely have similar issues when I shuffle addresses like that.

Title: Re: BRX Pings failing
Post by: JeffS on July 23, 2021, 01:42:52 PM

Is the ARP cache something stored in the BRX?  Possible to clear it for a specific IP, or the entire cache?

Title: Re: BRX Pings failing
Post by: BobO on July 23, 2021, 02:29:53 PM

Quote from: JeffS on July 23, 2021, 01:42:52 PM

Is the ARP cache something stored in the BRX?  Possible to clear it for a specific IP, or the entire cache?

It's in the IP stack and not directly accessible by you, or even me for the matter. I have modded the stack before and ended up re-releasing firmware because I did things with unexpected side effects.