Webinar topic: Troubleshooting Layer 2 Ethernet Problem: Loop, Broadcast, Security Presenter: Achmad Mardiansyah, M. Taufik Nurhuda In this webinar series, Troubleshooting Layer 2 Ethernet Problem: Loop, Broadcast, Security Please share your feedback or webinar ideas here: http://bit.ly/glcfeedback Check our schedule for future events: https://www.glcnetworks.com/en/schedule/ Follow our social media for updates: Facebook, Instagram, YouTube Channel, and telegram also discord Recording available on Youtube https://youtu.be/G4IuMNaJZLY

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Troubleshooting
Layer 2 ethernet
problem:
loop, broadcast,
security
GLC Webinar,
11 nov 2021
Achmad Mardiansyah
achmad@glcnetworks.com
GLC Networks, Indonesia
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Source: mikrotik.com

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Agenda
● Introduction
● Review prerequisite knowledge
● Ethernet technologies
● Ethernet issues
● Live practice
● Q & A
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introduction
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What is GLC?
● Garda Lintas Cakrawala (www.glcnetworks.com)
● Based in Bandung, Indonesia
● Areas: Training, IT Consulting
● Certified partner for: Mikrotik, Ubiquity, Linux foundation
● Product: GLC radius manager
● Regular event
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Trainer Introduction
● Name: Achmad Mardiansyah
● Base: bandung, Indonesia
● Linux user since 1999, mikrotik user since 2007, UBNT
2011
● Mikrotik Certified Trainer
(MTCNA/RE/WE/UME/INE/TCE/IPv6)
● Mikrotik/Linux Certified Consultant
● Website contributor: achmadjournal.com, mikrotik.tips,
asysadmin.tips
● More info:
http://au.linkedin.com/in/achmadmardiansyah
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Past experience
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● 2021 (Congo DRC, Malaysia): network support,
radius/billing integration
● 2020 (Congo DRC, Malaysia): IOT integration,
network automation
● 2019, Congo (DRC): build a wireless ISP from
ground-up
● 2018, Malaysia: network revamp, develop billing
solution and integration, setup dynamic routing
● 2017, Libya (north africa): remote wireless migration
for a new Wireless ISP
● 2016, United Kingdom: workshop for wireless ISP,
migrating a bridged to routed network

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About GLC webinar?
● First webinar: january 1, 2010 (title:
tahun baru bersama solaris - new year
with solaris OS)
● As a sharing event with various topics:
linux, networking, wireless, database,
programming, etc
● Regular schedule
● Irregular schedule: as needed
● Checking schedule:
http://www.glcnetworks.com/schedule
● You are invited to be a presenter
○ No need to be an expert
○ This is a forum for sharing: knowledge,
experiences, information
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Please introduce yourself
● Your name
● Your company/university?
● Your networking experience?
● Your mikrotik experience?
● Your expectation from this course?
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Prerequisite
● This presentation some prerequisite knowledge
● We assume you already understand:
○ How browsing works
○ Computer networks
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Review prerequisite knowledge
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Your ISP and you
● ISP is an organisation that is part of internet that provides connectivity to their
customers
○ Identified by their AS (Autonomous System) number
○ Identified by their IP address block
● When you connect to internet, you will use your ISP’s address
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Your ISP. and you
are part of them
other
ISP
other
ISP
google
facebook

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At your ISP (physical connection)
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Border
router
Other
ISP
Other
ISP
Access
router
Access
router
customer customer customer
Access network: GPON, WLAN,
FO, GSM, ethernet, etc

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7 OSI layer & protocol
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● OSI layer Is a conceptual model from ISO
(International Standard Organization) for project
OSI (Open System Interconnection)
● When you send a message with a courier, you
need to add more info to get your message arrived
at the destination (This process is called
encapsulation)
● What is protocol
○ Is a set of rules for communication
○ Available on each layer
● Communication consist of series encapsulation
○ SDU: service data unit (before PDU)
○ PDU: protocol data unit (after header is added)

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Internet encapsulation
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Layered model (TCP/IP vs ISO) and encapsulation
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/ datagram

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Layer 4 header (which one is TCP?)
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Layer 3 header (which one is IPv4?)
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Ethernet header (which is the MTU?)
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802.11 header
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Did you notice?
● There is a big overhead on encapsulation process
● More encapsulation means less payload?
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ethernet
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Ethernet specs
● Defined by IEEE 802.3
● Media:
○ Coaxial cable
○ Twisted pair
○ Fiber optic
● Devices required:
○ Bridge / switch
○ HUB
● Everyone likes it!!
○ Affordable
○ Easy to install
○ Easy maintenance
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How ethernet works (CSMA/CD)
● Carrier Sense Multiple Access / Collision
Detection (CSMA/CD)
○ Every host do not know when other send data
○ Before sending data, host check the shared medium
○ Every host only knows when collision happens
● You will have:
○ Collision domain
■ Area where collision happens
■ Can use any frame
○ Broadcast domain
■ Area when broadcast happens
■ Using broadcast frame
● CSMA/CD != CSMA/CA
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How ethernet works (ARP)
● Address resolution protocol (ARP)
● Bridging between IPv4 and MAC
address
● Requires broadcast frame
● Will be eliminated in IPv6
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Source: ipcisco.com

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Ethernet evolution (1)
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Ethernet evolution (2)
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Ethernet issues
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Collision domain
● Area where collision happens
● Some ideas:
○ Using switched network
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Source: devto.com

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Broadcast domain
● An area where broadcast happens
● Try use 5-4-3-2-1 rules
● Some ideas:
○ Using router to split segments
○ Port isolation on switch
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Loop
● A condition when frame is forwarded in the
media
● Will stop until one of cable is removed
● Some ideas:
○ Do not use traditional switch
○ activate STP between switch
○ Port isolation
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Security
● Apply security on network
● Authentication
● Authorization
● Accounting
● Ideas:
○ Dot1x
○ Captive portal
○ MAC address authentication
○ Prevent rogue DHCP server
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Ethernet troubleshooting
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Troubleshooting
● Approach: bottom-up (OSI layer)
● Layer 1
○ Check cabling: crimping/splicing quality, all pins
are OK
● Layer 2
○ Check looping, collision, broadcast
● Layer 3
○ Check reachability: ping
○ Check path: traceroute
● Layer 4:
○ Check port reachability
● Layer 5-6-7 (app)
○ Check application message
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How mikrotik can help (1)
● Check statistics on RouterOS
● Cable test
● Duplex mismatch
● Speed flapping
●
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06:01:47 interface,info ether3 link down
06:01:50 interface,info ether3 link up (speed 100M, full duplex)
06:02:08 interface,info ether3 link down
06:02:10 interface,info ether3 link up (speed 10M, half duplex)
06:03:03 interface,info ether3 link down
06:03:06 interface,info ether3 link up (speed 100M, full duplex)
06:03:23 interface,info ether3 link down
06:03:25 interface,info ether3 link up (speed 10M, half duplex)
06:03:30 interface,info ether3 link down
06:03:32 interface,info ether3 link up (speed 100M, full duplex)
06:03:50 interface,info ether3 link down
06:03:52 interface,info ether3 link up (speed 10M, half duplex)
06:04:59 interface,info ether3 link down
06:05:01 interface,info ether3 link up (speed 100M, full duplex)
06:05:19 interface,info ether3 link down
06:05:21 interface,info ether3 link up (speed 10M, half duplex)

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How mikrotik can help (2)
● Flow control
● Loop protect
● Check Log
● Graphing
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●
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LIVE practice
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preparation
● SSH client
● SSH parameters
○ SSH address
○ SSH port
○ SSH username
○ SSH password
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Q & A
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Interested? Just come to our training...
● Topics are arranged in systematic and logical way
● You will learn from experienced teacher
● Not only learn the materials, but also sharing experiences, best-practices, and
networking
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End of slides
● Thank you for your attention
● Please submit your feedback: http://bit.ly/glcfeedback
● Find our further event on our website : https://www.glcnetworks.com/en/
● Like our facebook page: https://www.facebook.com/glcnetworks
● Slide: https://www.slideshare.net/glcnetworks/
● Discord (bahasa indonesia): (https://discord.gg/6MZ3KUHHBX)
● Recording (youtube): https://www.youtube.com/c/GLCNetworks
● Stay tune with our schedule
● Any questions?
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