Administration -> Sysctl

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sapphireweb
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PostPosted: Sun Mar 20, 2022 20:22    Post subject: Administration -> Sysctl Reply with quote
Linksys - wrt1900ac
Firmware: DD-WRT v3.0-r48432 std (03/01/22)


First, forgive me if this has already been answered, and point me to the link. I have spent 3-hours or so trying to find this. I can't believe I am the only one that has this question.

Where do I find a definition, and valid values for the fields on the Administration -> Sysctl page. (sysctl.asp)

Thank You.
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blkt
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PostPosted: Sun Mar 20, 2022 21:55    Post subject: Reply with quote
Research each one at a time and it is likely you want to keep all defaults or as-is except disable these two.

net.ipv4.tcp_tw_recycle
net.ipv4.tcp_tw_reuse

nvram show | grep tcp_tw
nvram set net.ipv4.tcp_tw_recycle=0
nvram set net.ipv4.tcp_tw_reuse=0
reboot
the-joker
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PostPosted: Mon Mar 21, 2022 6:04    Post subject: Reply with quote
Generally speaking if you want to know what each value is for, on a regular Linux distro you can open the /etc/sysctl.conf in any text editor and read the comments for each option.

If something is not on that file, just google the string Im sure you will have plenty hits.

Unless you know what you're doing I dont recommend messing around with these values.

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the-joker
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PostPosted: Sun Apr 03, 2022 9:38    Post subject: Reply with quote
Also mind that net.ipv4.tcp_tw_recycle may not be available in all routers, its not in mine and setting it may lead to unknown behavior.
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kernel-panic69
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PostPosted: Sun Apr 03, 2022 11:37    Post subject: Reply with quote
Both parameters are available on 4MB flash images AFAIK; not sure why it's not available on your device(s).
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blkt
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PostPosted: Mon Apr 04, 2022 5:00    Post subject: Reply with quote
"Good news tcp recycle will be disabled by default in the next build to address GUI issue."

Starting 44978 changeset 44991 adds new list, then 47246 disables and 47247 blacklists.

Depends kernel version, build installed and configuration generated from previous builds.

You know those who never reset 'nvram show | grep tcp_tw' exists here for good reason.
the-joker
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PostPosted: Mon Apr 04, 2022 8:33    Post subject: Reply with quote
This is not just DD-WRT, Red Hat RHEL 8 doesn't have it (last I checked) and probably many others.

Also definetly recommend a nvram reset after such sweeping changes to nvram values are done.

Without actually following the development of DD-WRT closely, for the general populous twice yearly nvram reset wouldn't be a farfetched bad piece of advice.

What we really need is a way to reconfigure the nvram quickly via command line based on settings / nvram strored variable that are hardly going to change, like static leases and other ACL's, security settings and MAC Filter lists etc.

I for one have a human readable config backup to do just this, because setting up from scratch is a pita. I can also easily do diffs between these to see how much has changed nvram side based on twice yearly, pre/post nvram reset.

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blkt
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PostPosted: Mon Apr 04, 2022 9:05    Post subject: Reply with quote
tcp_tw_recycle removed in 4.12 and yes yearly reconfig is considered especially if major changes occurred.

To go as far to as jump through additional hoops to avoid manual configure from scratch, to each their own.
the-joker
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PostPosted: Mon Apr 04, 2022 9:37    Post subject: Reply with quote
Depends, if your specific usage and config you notice or not possible issues because of all the crud left behind. Most people dont notice anything until they try to do something else.

Just look trough reports on build threads, where ppl report no issues and indeed there are, I found severe bugs not long ago 3 builds back and on build reports threads everyone was happy, just may not be immediately obvious due to their config/usage or because in all honesty I doubt anything beyond works/dont work is actually tested.
Doesnt mean those issues were caused by nvram values alone, but there we are.

But yea, to each their own, Im not losing sleep over what others do or dont.

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kernel-panic69
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PostPosted: Mon Apr 04, 2022 14:10    Post subject: Reply with quote
blkt wrote:
tcp_tw_recycle removed in 4.12

Which only applies to x86* builds, unless these patches/changes have been back-ported to 4.9.x and 4.4.x kernels in DD-WRT. Again, the item is still there on everything I have running DD-WRT, so the comment that it doesn't exist on a device running 4.4 seems amiss to me. Visual proof via screenshot works wonders, as is noted by you and your pseudo alter-ego in the UK.

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the-joker
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PostPosted: Mon Apr 04, 2022 16:19    Post subject: Reply with quote
My results, indeed I reset nvram recently 4 build ago

No recycle.

uname -a
Linux Nexus 4.4.302 #5645 SMP Wed Mar 30 21:22:21 +07 2022 armv7l DD-WRT

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Last edited by the-joker on Tue Apr 05, 2022 8:25; edited 2 times in total
ho1Aetoo
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PostPosted: Mon Apr 04, 2022 16:35    Post subject: Reply with quote
and it is not present in the kernel either?

Code:
cat /proc/sys/net/ipv4/tcp_tw_recycle


The setting was completely removed in 2017 in kernel 4.12, as mentioned above.
the-joker
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PostPosted: Mon Apr 04, 2022 16:46    Post subject: Reply with quote
kernel side it exists as 0
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kernel-panic69
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PostPosted: Mon Apr 04, 2022 21:19    Post subject: Reply with quote
An image of the output of nvram show | grep tcp would've sufficed instead of an animated gif that I cannot really focus on enough to read clearly, thanks. Rolling Eyes
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