topic Re: Problem with port congestion in ExtremeSwitching (EXOS/Switch Engine)

Problem with port congestion

Baroo — Fri, 17 May 2019 15:09:09 GMT

I`ve got two x440-24t switches in one city and two 1G uplink connections to the other city from these switches. When I configure the traffic between cities (around 200-300 Mb/s) to go through connection numer one (over DWDM form ISP1) everyting goes OK. However when I configure the same traffic to go through connection numer 2 (probably MPLS link over Alcatel switches form ISP2) port congestion counter starts incrementing (typicall when traffic reaches above 200 Mb/s).
I measured the link with JDSU Ethernet tester between SFP modules and it does not shows any errors. I turned off rx flow control with no luck. How can I futher debug this problem.

Re: Problem with port congestion

EtherMAN — Mon, 20 May 2019 23:26:42 GMT

First you must understand what the port congestion counter is. It ss dropped packet on the ingress side of any port where the buffer gets overrun so bad that packets are dropped.

So first question is what port is the congestion showing up on?? handoff port or interconnection ports?

do you have a bandwidth profile on the 440 limiting the service?

Re: Problem with port congestion

Baroo — Mon, 27 May 2019 13:58:11 GMT

I`ve found similar problem on the other port in my network. Let say I have topology like this:
BGP1 router (eth1) ---- (port 1) x440 switch (port 2) ------ (eth0) ACCESS1 router
In this scenario port congestion counters inreases on the port 2. What does this mean for me? Does this mean that BGP1 can`t handle traffic passing from ACCESS1?

Re: Problem with port congestion

EtherMAN — Wed, 29 May 2019 02:12:38 GMT

Congestion packets dropped on any switch are only packets dropped inside switch due to buffer being overrun on a physical interface. More than likely you are having a micro burst that is overruning the buffers... Link to how to look for this https://extremeportal.force.com/ExtrArticleDetail?n=000010163

another link to steps to take for packet lose https://gtacknowledge.extremenetworks.com/articles/Solution/Prevent-packet-drops

Again congestion drops on in the switch fabric when the buffers get overrun... Only Egress traffic on port and these switches all forward traffic at wirespeed so somehow some where there is more traffic in the switch than the interface speed can send to the adjacent switch / router. I did read a couple of post where flow control when enable can have adverse effects if the device you are sending traffic to keeps telling the switch to slow down a with a pause frame

Lots of other info in our knowledge base if you just search for port congestion.

Re: Problem with port congestion

Baroo — Wed, 29 May 2019 14:43:48 GMT

Thanks for your help. I`ve figured out that:
enable flow-control tx-pause port 2
solved the problem. Seems like switch sending pause frame to router makes that ok.