Spectrum 10.4 on RHEL 7 - TFTP server and large UDP block size

[James Brunner]

Hi all,

We've spun up a new RHEL7 Spectrum 10.4 SS server and all works fine except NCM capture for some devices. Never had this issue on our current Windows install but that's using the s'winds TFTP server :)

So, we're running the tftp-server (5.2-22) under xinetd (2.3.15-13) with all the right settings and most of our Cisco devices capture configs fine.

The ones that fail have a locally set tftp blocksize of 8192 for legacy reasons. I tried to set the in.tftd's blocksize in the /etc/xinetd.d/tftp file way up to 12k as below [way under the 65464 maximum but enough to satisfy these devices]

server_args = -c -s /tftproot -u svc-spectrum --blocksize 12288

But while the xinetd/tftp restarts and still works for the devices using the default blocksize anything set with a blocksize larger than 1468 fails. I've tried larger (32768) and smaller overrides (2048) while changing the devices to match, as well as changing the server_args from --blocksize to -B but no luck.

What do you do if running under RHEL to make this work? I can't be the only one.

Regards, JB.

[James Brunner]

So after more digging, it's a problem between certain Cisco devices and the RHEL TFTP server (ISR 4xxx were ok but 3650, 3850, 9200 and 9300's were not). We had no option but to adjust all Cisco devices to a blocksize of 1024. This now works perfectly for all our kit. We just have to remind our teams to execute file copies/pulls up to the switches using FTP not TFTP as our TCP window scaling is much larger allowing fast transfers over the long fat pipes.

Hope this helps someone else in the future.

JB.

[Johan Hedlund]

I ran into this issue on Spectrum 10.3.1 as well.

But the problem itself doesn't seem (to my knowledge) to be Spectrum related.
The issue surfaced when RHEL tftp-server 5.2-22 was released. Reverting to 5.2-13 fixed the issue.

[James Brunner]

That worked perfectly with the larger blocksizes.

I see Jan did lots of work on 5.2-14 to -22 on RFC7440 TFTP Windowsize Option but something obviously broke!

For anyone else, to wind back, use 'yum downgrade tftp-server-5.2-13.el7.x86_64'.

Thanks for this tip.

JB.