Cisco Cisco Nexus 7700 F2-Series 48-Port 1G and 10G Ethernet Module Enhanced Troubleshooting Guide

Contents

Introduction

Problem

Solution

Related Cisco Support Community Discussions

Introduction

The purpose of this document is to show how to modify ingress buffers on the Cisco Nexus 7000
(N7k) Cisco Nexus 7000 48-Port 1 and 10 Gigabit Ethernet F2-Series Module (F2) and Cisco
Nexus 7000 Enhanced F2-Series 48-Port Fiber 1 and 10 Gigabit Ethernet Module (F2e) linecards
for Virtual Lane 3 (VL3).

Also, you will see the amount of ingress buffering capacity you gain for VL3 after modifying these
values.

Problem

Using Fiber Channel over Ethernet (FCoE) multihop connections between Datacenters over
distances greater than 2 kilometers can result in input drops. By default, the F2/F2e linecards have
0 pages in the latency buffer to queue packets after pause is sent and this will lead to input drops
on long distance FCoE multihop interfaces.

The latency buffer is defined as follows:

PL_STOP - HWM (PL_Pause) = LB (Latency Buffer)

You'll notice the values mentioned above are displayed as pages. Each page is roughly 384 bytes.

Notice below, the ingress buffer capacity of VL3 with the default FCoE QoS policy:

module-10# show hardware internal mac port 1 qos configuration | begin IB | end EB

Port page limit : 3584 (1376256 Bytes)

VL# HWM pages(bytes) LWM pages(bytes) Used PL_STOP(HWM & LWM) SPAN

pages THR

0 1107 ( 425088) 1035 ( 397440) 0 1107 1035 100

1 2 ( 768) 1 ( 384) 0 2 1 1

2 2 ( 768) 1 ( 384) 0 2 1 1

3 1053 ( 404352) 1029 ( 395136) 0 1053 1029 100

4 1107 ( 425088) 1083 ( 415872) 0 1107 1083 100

5 231 ( 88704) 159 ( 61056) 0 231 159 57

6 2 ( 768) 1 ( 384) 0 2 1 1

7 2 ( 768) 1 ( 384) 0 2 1 1

Credited DWRR WT: 216 (0xd8) Uncredited DWRR WT: 144 (0x90)

DWRR honor UC = FALSE

Leak Lo weight = 0xd8, enabled = FALSE