Cisco N7700 Configuration

Contents

Introduction
Topology
Determine the Ingress Forwarding Engine
Configure the Trigger
Start the Capture
Interpret the Results
Additional Verification

Introduction

This document describes the steps used in order to perform an ELAM on Cisco Nexus 7700
(N7700) M3 modules, explains the most relevant outputs, and describes how to interpret the
results.

Tip: Refer to the ELAM Overview document for an overview on ELAM.

Topology

In this example, a host on VLAN 2500 (10.0.5.101), port Eth4/1 sends an Internet Control
Message Protocol (ICMP) request to a host on VLAN 55 (10.0.3.101), port Eth3/5. ELAM is used
in order to capture this single packet from 10.0.5.101 to 10.0.3.101. It is important to remember
that ELAM allows you to capture a single frame.

In order to perform an ELAM on the N7K, you must first connect to the appropriate module (this
requires the network-admin privilege):

N7700# attach module 4
Attaching to module 4 ...
module-4#

Determine the Ingress Forwarding Engine

Traffic is expected to ingress the switch on port Eth4/1. When you check the modules in the
system, you see that Module 4 is an M3 module. It is important to remember that the N7K is fully­distributed, and that the modules, not the supervisor, make the forwarding decisions for dataplane

traffic.

N7700# show module
Mod Ports Module-Type Model Status

--- ----- ----------------------------------- ------------------ ---------­1 12 100 Gbps Ethernet Module N77-F312CK-26 ok
3 48 1/10 Gbps Ethernet Module N77-M348XP-23L ok 4 24 10/40 Gbps Ethernet Module
N77-M324FQ-25L ok
5 0 Supervisor Module-2 N77-SUP2E active *
6 0 Supervisor Module-2 N77-SUP2E ha-standby
7 24 10/40 Gbps Ethernet Module N77-F324FQ-25 ok

Mod Sw Hw

--- --------------- -----­1 7.3(0)DX(1) 1.1
3 7.3(0)DX(1) 1.1 4 7.3(0)DX(1) 1.0 5 7.3(0)DX(1) 1.2 6 7.3(0)DX(1) 1.2 7 7.3(0)DX(1) 1.0

For M-Series modules, perform the ELAM on the Layer 2 (L2) Forwarding Engine (FE) with
internal codename F4. Note that the L2 FE Data Bus (DBUS) contains the original header
information before the L2 and Layer 3 (L3) lookups, and the Result Bus (RBUS) contains the
results after both L3 and L2 lookups.

N7K M3 modules can use multiple FEs for each module, so you must determine the F4 ASIC that
is used for the FE on port Eth4/1. Enter this command in order to verify this:

module-4# show hardware internal dev-port-map
(some output omitted)

-------------------------------------------------------------- CARD_TYPE: 24 port 40G >Front
Panel ports:24 -------------------------------------------------------------- Device name Dev
role Abbr num_inst: -------------------------------------------------------------- > SLF L3
Driver DEV_LAYER_3_LOOKUP L3LKP 4 > SLF L2FWD driver DEV_LAYER_2_LOOKUP L2LKP 4
+-----------------------------------------------------------------------+
+----------------+++FRONT PANEL PORT TO ASIC INSTANCE MAP+++------------+
+-----------------------------------------------------------------------+
FP port | PHYS | MAC_0 | RWR_0 | L2LKP | L3LKP | QUEUE |SWICHF
1 0 0 0 0 0 0,1
2 0 0 0 0 0 0,1
3 0 0 0 0 0 0,1

In the output, you can see that port Eth4/1 is on F4 (L2LKP) instance 0. On the N77-M312CQ-26L
module, there are 6 F4 ASICs with 2 ports in each port group. On the N77-M324FQ-25L module,
there are 4 F4 ASICs with 6 ports in each port group. The N77-M348XP-23L module has 2 F4
ASICs with 12 ports in each port group.

Note: Just like F-series modules, M3 module ELAM syntax uses 0-based values. This is not
the case for M1 and M2 modules, which use 1-based values.

module-4# elam asic f4 instance 0
module-4(f4-elam)# layer2
module-4(f4-l2-elam)#

Configure the Trigger

The F4 ASIC supports ELAM triggers for IPv4, IPv6, and others. The ELAM trigger must align with
the frame type. If the frame is an IPv4 frame, then the trigger must also be IPv4. An IPv4 frame is
not captured with an other trigger. The same logic applies to IPv6.

With Nexus Operating Systems (NX-OS), you can use the question mark character in order to
separate the ELAM trigger:

module-4(f4-l2-elam)# trigger dbus ipv4 ingress if ?