Conntrack table memory usage

[Denna]

@RMerlin,

I've been looking at ways to minimize router resource usage caused by external Internet hosts.

One of the ways to minimize CPU usage and conntrack table entries was to implement the following rule.

iptables -t mangle -I PREROUTING -i <wan_face> -m state --state NEW -j DROP

On an Asus RT-AC88U, if you run the following command ...

sysctl net.ipv4.netfilter.ip_conntrack_max

... you get 300,000.

Does that mean this router is configured with a maximum of 300,000 simultaneous connections ?

If each conntrack entry is 350 bytes, doesn't that amount to more than 100 MB of memory usage ?

Is that right ?​

 

[Denna]

@RMerlin,

Is the above setting a typo or the expected value for Asuswrt / Asuswrt-Merlin ?​

 

[john9527]

It's the normal default......you can change it on the Tools > Other Settings page.

 

[Denna]

@john9527,

Thanks for the reply.

Are 300,000 connections for a home router really necessary ?

That's a lot of memory to be assigned to connection tracking.​

 

[john9527]

@john9527,

Thanks for the reply.

Are 300,000 connections for a home router really necessary ?

That's a lot of memory to be assigned to connection tracking.​

IMHO, it's a great marketing bullet point, and nothing more.

I think most of the memory is dynamically allocated, so that probably isn't a big concern. If you do a search, I seem to remember a thread that discussed the other potential performance impacts of using that large a value. Personally, I have it set to the kernel default, which on my system is about 30,000. If you look on the Tools > Sysinfo page, you can see the actual number of connections you are actually using.

 

[Denna]

What WebGUI is reporting now ...

Alert ! Alert ! I only have 299,866 available connections left !

I seriously believe 300,000 max connections is a typo, because the CPU(s) need to support that many connections is probably not in this router.

What application(s) could possible use that many connections - streaming, gaming ? By how many clients ?