topic Re: ISE: Recommended Values for Connection Limit, Rate limit and Syn-f in Network Access Control

ISE: Recommended Values for Connection Limit, Rate limit and Syn-flood

Nikhil Jadhav — Mon, 22 Nov 2021 00:40:12 GMT

Hello Everyone,

I am working with a customer to ensure ISE is configured with the best practices.

Can anyone please help me out with the recommended values for Connection Limit, Rate Limit and SYN-Flood?

Also, Is there a way to calculate Average TCP, UDP, ICMP packets received by ISE?

Thank you,

Re: ISE: Recommended Values for Connection Limit, Rate limit and Syn-f

Arne Bier — Wed, 24 Nov 2021 01:16:23 GMT

Hi @Nikhil Jadhav

Great question.

I would recommend running a TCP dump on the PSNs at busy-hour and then analysing the results in wireshark (filter on TCP syn packets).

Or run a report on ISE to see how many requests you're getting per node per second.

I guess the danger in setting these values is that you could end up making the service worse if the values are too low.

If you think about it, a PSN that is hosting a web portal is probably a good candidate for SYN flood protection. It would be quite a busy node that is processing 100 SYN packets per second. You could start with that and then use a tool like jMeter to try and hammer the PSN with a SYN flood to test that your config works ... in a lab of course 😉

As for the connection limits for UDP etc - not sure if I would set those.

A some what useless guide here ..

Re: ISE: Recommended Values for Connection Limit, Rate limit and Syn-f

thomas — Sun, 05 Dec 2021 00:06:47 GMT

> Can anyone please help me out with the recommended values for Connection Limit, Rate Limit and SYN-Flood?

We do not have any specific guidance. ISE is a AAA server with TACACS and RADIUS request-response protocols. Rates are environment and scenario-dependent (university wireless at the top of the hour vs wired manufacturing IOT). TACACS rates can be slow with human users and insane with automation. RADIUS supports many EAP tunnels and methods, each with their own performance rates.

> Also, Is there a way to calculate Average TCP, UDP, ICMP packets received by ISE?

Use a sniffer or run a packet capture on your ISE nodes? Operations > Troubleshoot > Diagnostic Tools > General Tools > TCP