ARP Basics (ARP picture book-1 from VisualLand Animations)

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ARP BasicARP tutorial with pictures
-1www.visualland.net

• Watch animation to learn networking.
• Visualize how ARP translates IP address into
  MAC. Watch interactions between ARP Request, ARP
  Reply, and ARP cache.
• This pictured tutorial takes screenshots from
  ARP Basic Animation.
• OK to republish this slide. Please use hyperlink
  to point to its source.

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ARP animations

1. ARP basic - update For behinners.
   Observing basic ip-mac binding interactions (ARP
   Request, ARP reply, ARP cache, ping
   encapsulation, ping command.)
2. ARP basic - no update Same as above. But the
   node receiving ARP Request does not update its
   ARP cache. (It's a vendor decision whether to
   update ARP cache when receiving RAP request).
3. ARP hub Three hosts are
   connected to a hub. Run ping to observe how ARP
   frames and ping packets are being flooded by
   hub.
4. ARP switch Three hosts are
   connected to a switch. Run ping to observe ARP
   frames are being flooded and switched by the
   switch.
5. ARP router gateway (Lab) Visualize how ARP
   discovers a MAC in a different subnet when hosts
   are connected to a router and the router is the
   default gateway.
6. ARP router proxy (Lab) Visualize how ARP
   discovers a MAC in a different subnet when hosts
   are connected to the same router but have no
   default gateway.
7. ARP spoofing (Theory) Visualize how a hacker
   can listen and corrupt IP-MAC bindings in
   other's ARP caches, and kidnap data.
8. ARP spoofing (Lab) Same as above. The
   animation data is captured from a simulation Lab
   (dynamips). Timing is realistic.

2019/9/18
www.visualland.net
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OverviewARP Basics Animation Link
Goal Visualize ARP activities of MAC lookup and
interactions of ARP request, ARP reply, ARP
cache?Ping command line. Topology Two hosts H1,
H2 are directly connected. There IP-MAC addresses
are (IP.H1, MAC.H1), (IP.H2, MAC.H2)
respectively. Steps 1) H1 ping H2 fails due to
ARP miss. H1 sends ARP Request to find out H2's
MAC. 2) H2 responds ARP Reply with
its MAC to H1. 3) H1 ping H2 again
and succeeds.
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H1 ping H2 ARP miss

• H1 ping H2. Ping prints its command message in
  H1's command window.
• To create Ping packet, H1 needs to know H2's MAC.
  But ARP cache does not have H2's MAC. Therefore,
  H1
• is unable to send ping out. This is called ARP
  miss. It's a common cause of packet loss.

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H1 sends ARP request
To find H2's MAC, H1 sends ARP Request and adds
an entry (IP.H2, Incomplete) in ARP cache. It
says I'm looking for H2's MAC. ARP Request
header includes a few parameters sender IP is
H1's IP, sender mac is H1's MAC, target IP is
H2's IP, target mac is 0. (You may click ARP
Request to see its headers).
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H2 responds ARP reply
After receiving ARP request, H2 adds H1's address
to its ARP cache as (IP.H1, MAC.H2). Then H2
checks ARP Request's protocol header and learns
that this query is for itself. H2 responds and
sends ARP Reply to H1. (Click ARP Reply to see
its protocol header)
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H1 recevies ARP reply
When receiving ARP Reply, H1 updates its ARP
cache and changes the entry (IP.H2, Incomplete)
to (IP.H2, Mac.H2).
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H1 ping H2 again
Now the first ping timeout. Ping prints a "." in
the H1 command window to indicate a timeout. Then
H1 sends next ping. No ARP miss this time. Ping
does find H2's MAC in ARP cache.
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H2 echo H1
When receiving ping, H2 sends an Echo to
respond. H2 is able to find H1's MAC in ARP
cache. No ARP miss for sending Echo.
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H1 receives echo
After receiving Echo, H1 prints a "!" to indicate
ping success.
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FAQ

• What is ARP?
• Why ARP?
• What is ARP cache?
• What are ARP commands?
• How is ARP related to encapsulation?
• ( answers in the Comments box )

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What is Vlabvisualland.net

• VLAB Virtual Lab
• Theory Visualize key points of network protocols
  to help beginners grasp the basic ideas quickly.
• Lab Visualize network activities with packets
  and router states captured from network
  simulators (dynamips, packet tracer, and ns2.
• Interactively control animation packet headers,
  protocol state tables.
• Vlab usage
• Self learning, teaching aids, lab book.