How to Limit Port Speed.

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metalguy
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Joined: 28 Jan 2016
Posts: 7

PostPosted: Sat May 25, 2019 18:27    Post subject: How to Limit Port Speed. Reply with quote
I just purchased a WRT1900AC and successfully flashed it with DDWRT 39827. I am replacing an old WRT54GL that was also flashed with DDWRT.

Connected to the WAN port (of the WRT54GL) was a SurfBeam 2 Satellite Modem. I was able to get an IP address from the modem when DDWRT was set to Auto DHCP on the WRT54GL.

I have now replaced the WRT54GL with the WRT1900AC with the exact same configuration. However, the auto DHCP (on the WAN port) receives and IP address of 0.0.0.0.

I have tried multiple devices and it seems that the only devices that work with the SurfBeam2 are the ones that have 100Mbps ports.

I want to rule out that the 1GB interface is causing the issue on the WRT1900AC. My question is, can I limit the WAN port to 100Mbps on the WRT1900AC?

If so, how do I go about doing it? I could not find anything at the moment on how to do so.
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pa3fat
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Joined: 25 Apr 2010
Posts: 84
Location: Valkenswaard, The Netherlands

PostPosted: Sat May 25, 2019 19:17    Post subject: Reply with quote
There isn't a real option in the settings i think.

But in the time between other responses:
- sometimes the ISP only supplies IP# every eg hour.
Toggling with devices will not bypass this. It's a matter of waiting.

- sometimes shutting down the IPS modem triggers this process and speeds things up. Did you unplug the power of this modem, waited eg 10 minutes and powered it up?

- sometimes mac addresses are set at the modem of the ISP enabling the connection. But i personally never encountered this myself.

Think all ports will negotiate the speed between them.

Hope this is of any help.
metalguy
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Joined: 28 Jan 2016
Posts: 7

PostPosted: Sat May 25, 2019 20:53    Post subject: Reply with quote
It's not a matter of waiting. Sad
The moment I plug the modem into any other device i get an IP address instantly.
Ah-Pin-Kor
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Joined: 19 Sep 2015
Posts: 237

PostPosted: Sun May 26, 2019 0:07    Post subject: Reply with quote
Since you have a WRT54G, you can turn it into a 10/100Mbps switch and place this between the modem and the wan port of the wrt1900ac. This should limit the connection to 100Mbps max. Connect the wrt1900ac wan port to a lan port of the switch, and connect the modem lan port to another lan port of the switch.

There are various tutorials on the web on how to turn the wrt56g into a switch. The basic important steps:
-backup your wrt54g config into your computer
-change the wrt54g lan IP into something that doesn't conflict with your wrt1900ac ip.
-disable the dhcp service in wrt54g
-don't plug anything to the wan port of wrt54g

_________________

Netgear R7800 kongpro 19.07 20190616 || Netgear R7000 35550M kongac (Client Bridge=5GHz, AP=2.4GHz)
Linksys WRT32X davidc502 OpenWrt || Linksys WRT1200ACv1 Gargoyle 1.11.x
Linksys WRT1900ACSv2 dd-wrt 39956
metalguy
DD-WRT Novice


Joined: 28 Jan 2016
Posts: 7

PostPosted: Sun May 26, 2019 0:30    Post subject: Reply with quote
I was thinking the same but I'm trying to limit the number of devices.
Ah-Pin-Kor
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Joined: 19 Sep 2015
Posts: 237

PostPosted: Sun May 26, 2019 0:50    Post subject: Reply with quote
It's just a temporary setup, just to prove your theory that the wan only works with 100Mbps. Once you have proved/disproved that, you can put the wrt54g back to original config.
Another way to force the link to 100Mbps max is that gigabit speed need all 4 twisted pairs of the cable. If you cut one of the pairs at the side, you will be left with less than 4 pairs and it won't negotiate to 1Gbps. From the pinouts, you can get a cheap cat 5 cable and cut wires connected to pins7&8.

100base-tx pinouts:

Pin 1: Transmit Data+
Pin 2: Transmit Data-
Pin 3: Receive Data+
Pin 4: Unused
Pin 5: Unused
Pin 6: Receive Data-
Pin 7: Unused
Pin 8: Unused

_________________

Netgear R7800 kongpro 19.07 20190616 || Netgear R7000 35550M kongac (Client Bridge=5GHz, AP=2.4GHz)
Linksys WRT32X davidc502 OpenWrt || Linksys WRT1200ACv1 Gargoyle 1.11.x
Linksys WRT1900ACSv2 dd-wrt 39956
metalguy
DD-WRT Novice


Joined: 28 Jan 2016
Posts: 7

PostPosted: Sun May 26, 2019 1:36    Post subject: Reply with quote
That's a great idea.
I'll use a cat 5 cable and that should force it to use 100mbps.
d0ug
DD-WRT Guru


Joined: 31 Jul 2015
Posts: 696

PostPosted: Wed May 29, 2019 5:46    Post subject: Reply with quote
metalguy wrote:
That's a great idea.
I'll use a cat 5 cable and that should force it to use 100mbps.


A properly wired cat5 will carry gigabit with no problems. Not best practice, but I have done it many times. Might be an issue at longer distances.

If you really want to force a link into 100mbps mode you need to actually snip the extra pairs in the cable that gitabit uses. Either slit the cable and cut the pairs going to the appropriate pins, or if you have a cable crimper, just crimp a new end with those pins disconnected.

The pins to disconnect are pins 4,5,7 and 8. On a properly made ethernet cable these will be the blue and brown pairs

metalguy
DD-WRT Novice


Joined: 28 Jan 2016
Posts: 7

PostPosted: Thu May 30, 2019 3:40    Post subject: Reply with quote
I was able to clip an Ethernet cord based on the diagram but to no avail. All devices that i connected with that clipped cable connected properly at 100mbps. However, when i connect my modem to my wrt1900ac with the modified cable, i still get 0.0.0.0.

Back to my original thought, can you limit the wan port speed on the wrt1900sac router running ddwrt?
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