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Lei Zhang
Cisco Employee
Cisco Employee
本帖最后由 leiz2 于 2018-3-19 16:28 编辑
一、简介
在排查网络丢包的故障时,我们可以用ELAM工具在数据包沿途设备抓包来定位被丢弃的数据包是被哪台设备所丢弃,也就是确定故障源。之后,对故障源进一步排查。本文主要介绍如何在N9K (Tahoe 芯片)配置ELAM,并且解释ELAM相关的输出信息。

二、拓扑
N93180 (Eth1/53, vlan 1235, 12.35.1.2) --- (Eth1/53, vlan 1235, 12.35.1.1) N92160
使用ping流量,N92160 >>>ping (icmp request)>>> N93180.

三、Lab 环境检查及确认
N93180# show module
Mod Ports Module-Type Model Status
--- ----- ------------------------------------- --------------------- ---------
1 54 48x10/25G + 6x40/100G Ethernet Module N9K-C93180YC-EX active * <<<<<<<<<<<<

Mod Sw Hw Slot
--- ---------------- ------ ----
1 7.0(3)I7(2) 1.0 NA <<<<<<<<<<<<软件版本为7.0(3)I7(2)

Mod MAC-Address(es) Serial-Num
--- -------------------------------------- ----------
1 00-a6-ca-09-a2-66 to 00-a6-ca-09-a2-b5 FDO203308E2

Mod Online Diag Status
--- ------------------
1 Pass

* this terminal session
N93180#
N93180# attach module 1<<<<<<<<<<<<<<<<
module-1# show hardware internal version <<<<<<<<<<<检查芯片信息
-------------------------------------------------------------------
Name InstanceNum Version Date
-------------------------------------------------------------------
Sugarbowl 0 0x02 <<<<<<<<<<<<为Tahoe芯片中的Sugarbowl芯片 (Tahoe芯片分为:Lacrosse, Davos, Sugarbowl)
IO FPGA 0 0x09 20161122
MI FPGA 0 0x04 20160317
CPLD1 0 0x04
CPLD2 0 0x04
module-1#
N93180# show run int vlan 1235<<<<<<<<<<<<<<

!Command: show running-config interface Vlan1235
!Time: Mon Mar 19 15:34:48 2018

version 7.0(3)I7(2)

interface Vlan1235
no shutdown
no ip redirects
ip address 12.35.1.2/24
no ipv6 redirects

N93180# show run int e1/53<<<<<<<<<<<<<<<<<物理口配置

!Command: show running-config interface Ethernet1/53
!Time: Mon Mar 19 15:34:55 2018

version 7.0(3)I7(2)

interface Ethernet1/53
switchport
switchport mode trunk
switchport trunk allowed vlan 1234-1235
no shutdown

N93180#
N93180# show ip arp 12.35.1.1<<<<<<<<<<<<<<<<<<检查arp

Flags: * - Adjacencies learnt on non-active FHRP router
+ - Adjacencies synced via CFSoE
# - Adjacencies Throttled for Glean
CP - Added via L2RIB, Control plane Adjacencies
PS - Added via L2RIB, Peer Sync
RO - Re-Originated Peer Sync Entry
D - Static Adjacencies attached to down interface

IP ARP Table
Total number of entries: 1
Address Age MAC Address Interface Flags
12.35.1.1 00:11:35 003a.7d7c.6a53 Vlan1235 <<<<<<<<<<<<
N93180#
N93180# show mac address-table vlan 1235 address 003a.7d7c.6a53<<<<<<<<<<<检查mac信息
Legend:
* - primary entry, G - Gateway MAC, (R) - Routed MAC, O - Overlay MAC
age - seconds since last seen,+ - primary entry using vPC Peer-Link,
(T) - True, (F) - False, C - ControlPlane MAC, ~ - vsan
VLAN MAC Address Type age Secure NTFY Ports
---------+-----------------+--------+---------+------+----+------------------
* 1235 003a.7d7c.6a53 dynamic 0 F F Eth1/53<<<<<<<<<<<<<<<物理出接口
N93180#
N93180# ping 12.35.1.1<<<<<<<<<<<<<<<<
PING 12.35.1.1 (12.35.1.1): 56 data bytes
64 bytes from 12.35.1.1: icmp_seq=0 ttl=254 time=0.968 ms
64 bytes from 12.35.1.1: icmp_seq=1 ttl=254 time=0.624 ms
64 bytes from 12.35.1.1: icmp_seq=2 ttl=254 time=0.899 ms
64 bytes from 12.35.1.1: icmp_seq=3 ttl=254 time=0.611 ms
64 bytes from 12.35.1.1: icmp_seq=4 ttl=254 time=0.928 ms

--- 12.35.1.1 ping statistics ---
5 packets transmitted, 5 packets received, 0.00% packet loss
round-trip min/avg/max = 0.611/0.806/0.968 ms
N93180#

四、ELAM的配置
N93180# debug platform internal tah elam <<<<<<<<<<<<<<进入ELAM模式
N93180(TAH-elam)# trigger init lu-a2d 1 in-select 6 out-select 0<<<<<<<<<<"in-select 6“ 参数可根据实际场景自定义,见本文底部附录
N93180(TAH-elam-insel6)# reset <<<<<<<<<<<<<<<<<防止以前配置过elam,即,旧elam配置干扰
N93180(TAH-elam-insel6)# set outer ipv4 src_ip 12.35.1.1 dst_ip 12.35.1.2 <<<<<<<<<<<<
N93180(TAH-elam-insel6)# start

对端N92160发起ping:
N92160# ping 12.35.1.2
PING 12.35.1.2 (12.35.1.2): 56 data bytes
64 bytes from 12.35.1.2: icmp_seq=0 ttl=254 time=0.972 ms
64 bytes from 12.35.1.2: icmp_seq=1 ttl=254 time=0.61 ms
64 bytes from 12.35.1.2: icmp_seq=2 ttl=254 time=0.846 ms
64 bytes from 12.35.1.2: icmp_seq=3 ttl=254 time=0.555 ms
64 bytes from 12.35.1.2: icmp_seq=4 ttl=254 time=0.534 ms

--- 12.35.1.2 ping statistics ---
5 packets transmitted, 5 packets received, 0.00% packet loss
round-trip min/avg/max = 0.534/0.703/0.972 ms

回到N93180检查ELAM结果:
N93180(TAH-elam-insel6)# report

SUGARBOWL ELAM REPORT SUMMARY
slot - 1, asic - 0, slice - 0
============================

Incoming Interface: Eth1/53<<<<<<<<<<<<<<<
Src Idx : 0x42, Src BD : 1235 <<<<<<<<<<<<<<
Outgoing Interface Info: dmod 0, dpid 0
Dst Idx : 0x5bf, Dst BD : 1235<<<<<<<<<<<<<<

Packet Type: IPv4<<<<<<<<<<<<<<

Dst MAC address: 00:A6:CA:09:A2:6D<<<<<<<<<<<<<<
Src MAC address: 00:3A:7D:7C:6A:53<<<<<<<<<<<<<<
.1q Tag0 VLAN: 1235, cos = 0x0<<<<<<<<<<<<<<

Dst IPv4 address: 12.35.1.2<<<<<<<<<<<<<<
Src IPv4 address: 12.35.1.1<<<<<<<<<<<<<<
Ver = 4, DSCP = 0, Don't Fragment = 0
Proto = 1, TTL = 255, More Fragments = 0
Hdr len = 20, Pkt len = 84, Checksum = 0xea01

L4 Protocol : 1
ICMP type : 8
ICMP code : 0
Sup hit: 1, Sup Idx : 2773

Drop Info:
----------

LUA:
LUB:
LUC:
LUD:
Final Drops:

ELAM not triggered yet on slot - 1, asic - 0, slice - 1

N93180(TAH-elam-insel6)#

至此,ELAM成功抓取到了N92160发起的ping包(icmp request),并可以查看该数据包头的相关信息。注意,ELAM一次只能抓取【一个】被elam配置match的数据包。本例中,ELAM抓到的为N92160发出的第一个ICMP request报文。

附录:
N93180(TAH-elam-insel6)# trigger init lu-a2d 1 in-select ? <<<<<<<<<<<<<<根据实际场景选择抓外层头/内层头信息
*** No matching command found in current mode, matching in (TAH-elam) mode ***
10 {outer l4, inner l4, ieth}
19 {udf_vec}
6 {outer l2, outer l3, outer l4}<<<<<<<<<<<<常用的:外层头
7 {inner l2, inner l3, inner l4}<<<<<<<<<<<<常用的:内层头
8 {outer l2, inner l2, ieth}
9 {outer l3, inner l3}

N93180(TAH-elam-insel6)# trigger init lu-a2d 1 in-select


N93180(TAH-elam-insel6)# set outer ? <<<<<<<<<<<<<<根据实际场景选择包类型
arp ARP Fields
fcoe FCoE Fields
ipv4 IPv4 Fields
ipv6 IPv6 Fields
l2 All Layer 2 Fields
l4 L4 Fields

Thanks!
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木吉法师
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对转发问题定位特别有用
Yanli Sun
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Community Manager
感谢专家分享:handshake
Luke Huang
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Cisco Employee
收藏,谢谢分享
minghwei
Cisco Employee
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