Internet speed drops after crossing ISL

[tato386]

I have an ASA that is setup with two ISPs and two inside vlans. ISP A is a 100/100MB fiber brought in on a Cisco router. ISP B is 1.0GB/50MB cable provider using small coax gateway. Both ISP devices are connected to ASA via 1GB ethernet. I use PBR so that each vlan is routed to its designated ISP. The vlans use dedicated (not trunk) ports on the ASA. ISP A is using default vlan. The inside vlan/interfaces are connected to a 3850 switch. The 3850 has 2x1GB LACP LAGs to 2960 switches.

So when I do Internet speed tests with a laptop connected to the 3850 the speeds are normal. I get high 90's for ISP A and 900+ with ISP B. All traffic is being scanned by Firepower module on ASA. However when I plug the laptop into any of the 2960s things get pretty weird. ISP A speeds are essentially unchanged. ISP B speed drops dramatically. Tests average about 180MB although sometimes I get as high as 300MB or so.

For troubleshooting I have turned off QoS, turned off Firepower, used different ports, removed links from LAG, hard coded speed/duplex settings, rebooted ISP gateway. Port statistics/errors seem OK. Nothing seems to have any effect at all.

Any other ideas?

Thanks,
Diego

[Georg Pauwen · Accepted solution]

Hello,

what is the CPU utilization of the 2960 when you are testing  ? Post the output of:

show proc cpu sorted | e0.00

Also, post the output of 'show interfaces x' where 'x' is the interface your laptop is connected to...

[tato386]

So after carefully reviewing the output of "show interfaces" I found this:  "32766 pause input" which indicated maybe I need to check the client I was doing the testing from.  I switched from testing with a laptop using USB to 1GB ethernet dongle to a desktop PC and retested.  Speeds using the desktop at the same 2960 switch and port tested consistently in the 900MB+ range!

At this point I am satisfied that the speeds at the 2960 are correct but it is very weird that it seems like the USB dongle has a problem going thru the ISL??

[paul driver]

Hello

Obviously this seems to suggest the bottleneck is the 2960 switch, As you have tried various things and no errors are being logged etc..It could be due to buggy software, Have you tried upgrading this switchs IOS or trying a another switch.