08-06-2020 08:53 PM
Hi
I have a live system which is failing
I have set up a test system replicating the live system, consisting of 2 x 3750G's.
A 3750G (Remote) connected to another 3750G (Host) with the following configuration
All switches are Version 12.2(55)SE12
interface GigabitEthernet1/0/1
description MSA Uplink
switchport trunk encapsulation dot1q
switchport trunk native vlan 5
switchport trunk allowed vlan 99,116
switchport mode trunk
speed 100
srr-queue bandwidth share 1 25 70 5
srr-queue bandwidth limit 50
queue-set 2
priority-queue out
mls qos trust dscp
macro description cisco-router
I am doing a speed test using Iperf 3 between 2 hosts on either side of the system using vlan 116
Remote (windows) Host (Linux)
using iperf3 -c 10.245.23.41 -u -b40
TEST 1
If I do the test Host -> Remote is see 40 Mbit transfer rate - No packets dropped on any interface
If I do the test Remote -> Host is see 12 Mbit transfer rate and matching packets dropped on the interface GigabitEthernet1/0/1
The packet loss is associated with DSCP 0 in
sh mls qos interface gigabitEthernet 1/0/1 statistics
Yes there is all sorts of other potential issues & settings but wait...
TEST2
But if i take the same Remote configuration and put it on a 3750 so interface 1 becomes
interface FastEthernet1/0/1
description MSA Uplink
switchport trunk encapsulation dot1q
switchport trunk native vlan 5
switchport trunk allowed vlan 99,116
switchport mode trunk
srr-queue bandwidth share 1 25 70 5
srr-queue bandwidth limit 50
queue-set 2
priority-queue out
mls qos trust dscp
macro description cisco-router
I see 40 Mbps in both directions.
TEST 3
On the original setup with 2 x 3750 G switches
If i leave the interfaces at GBit and send 400M I see no packet loss
CONCLUSIONS
My switch configuration in TEST1 is valid as it works with TEST2 so my mls qos, buffers etc configuration are ok, because TEST 2 works
As TEST3 works, it seems like the SRR functions don't like the speed 100
Remote config attached
Anyone got any ideas how to fix this so I can get speed 100 and SRR woorking in the live system ?
Thanks in Advance
Mark
08-07-2020 07:24 AM - edited 08-07-2020 07:28 AM
if you use "speed 100 " on the 3750G's then "automagically" also duplex negotiation is disabled
-> this may result in a duplex mismatch with the remote side (which is still set to auto?), hence the difference in throughput
on the normal 3750 you do not use speed 100 so there is no duplex mismatch.; the same on two 3750G's
=> use auto/auto or speed+duplex on both sides of the link
08-07-2020 09:17 AM
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