Posted: Mon Jul 08, 2019 17:11 Post subject: Increased latency for static route
I have a secondary router behind my DD-WRT (WRT1900AC V1). For the subnet behind that secondary router, I did a simple static route in the DD-WRT interface. While the route works (PC on DD-WRT LAN can ping other subnet and vice versa), there is about 16ms of added latency when bouncing between subnets. I can confirm the DD-WRT is causing the latency because if I have an OSPF relationship between two routers underneath the DD-WRT (thereby eliminating the need to hop through the DD-WRT), the latency goes down to 1ms (as expected on a wired network). But if the packet has to traverse through the DD-WRT, it adds 16ms of latency. Any ideas on what would be causing this?
Posted: Mon Jul 08, 2019 18:05 Post subject: Re: Increased latency for static route
rcraig114 wrote:
I have a secondary router behind my DD-WRT (WRT1900AC V1). For the subnet behind that secondary router, I did a simple static route in the DD-WRT interface. While the route works (PC on DD-WRT LAN can ping other subnet and vice versa), there is about 16ms of added latency when bouncing between subnets. I can confirm the DD-WRT is causing the latency because if I have an OSPF relationship between two routers underneath the DD-WRT (thereby eliminating the need to hop through the DD-WRT), the latency goes down to 1ms (as expected on a wired network). But if the packet has to traverse through the DD-WRT, it adds 16ms of latency. Any ideas on what would be causing this?
Robert
See my comment in the "fed up frustrated" thread below. It's something to do with AMSDU I think.
On these builds of open wrt it has been disabled for the 1900 models.
https://dc502wrt.org/
I have found latency is normal on 2.4GHz and adds c.20ms on 5GHz
Oh yeah, it’s a good cable. I can ping something on the same subnet using the same path and it’s 1ms. I know it’s a software problem because if I have a ping going and hit save/apply on the router for something, for a few brief seconds the latency drops back down to 1ms. But you can tell that as soon as the processor finishes doing whatever, it goes back up to 16ms.
Joined: 13 Aug 2013 Posts: 6870 Location: Romerike, Norway
Posted: Tue Jul 09, 2019 16:29 Post subject:
What is happening here is:
The PC connected to the LAN of the dd-wrt router tries to connect to a node behind the secondary router.
As the PC have the dd-wrt router as default gateway, it will try to send the packet to it. The dd-wrt router will reply back. I am not the router to forward this packet. You have to send it to the secondary router. The PC will then send the packet to the secondary router which will forward it to the correct sub-net.