MAC Address Tables on Connected Switches

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Presentation transcript:

5.2.1.4 - MAC Address Tables on Connected Switches

S1 MAC Address Table S2 MAC Address Table Port MAC Address Port MAC Address Internet S1 1 2 3 4 S2 1 2 3 4 Router 1 2 MAC 00-0D A B C MAC 00-0A MAC 00-0B MAC 00-0C Destination MAC 00-0B Source MAC 00-0A Type Data FCS For every Ethernet frame that enters a port, the switch will: Step 1: Learn (Building the MAC address table) Switch learns by examining the source MAC address If not in MAC address table, then add it along with incoming port number If in MAC address table, reset 5 minute timer PC-A sends a frame to PC-B The fame is received by switch S1

S1 MAC Address Table S2 MAC Address Table Port MAC Address Port MAC Address Internet 1 00-0A S1 1 2 3 4 S2 1 2 3 4 Router 1 2 MAC 00-0D A B C MAC 00-0A MAC 00-0B MAC 00-0C Destination MAC 00-0B Source MAC 00-0A Type Data FCS For every Ethernet frame that enters a port, the switch will: Step 1: Learn (Building the MAC address table) Switch learns by examining the source MAC address If not in MAC address table, then add it along with incoming port number If in MAC address table, reset 5 minute timer Switch S1 sees if it has something to learn by examining the source MAC address The source MAC address is not in its MAC address table S1 adds the source MAC address 00-0A and the incoming port 1 to its MAC address table

S1 MAC Address Table S2 MAC Address Table Port MAC Address Port MAC Address Internet 1 00-0A S1 1 2 3 4 S2 1 2 3 4 Router 1 2 MAC 00-0D A B C MAC 00-0A MAC 00-0B MAC 00-0C Destination MAC 00-0B Source MAC 00-0A Type Data FCS Step 2: Forwarding the frame (Using the MAC address table) Switch forwards by examining the destination MAC address If broadcast/multicast MAC address, flood out all ports except the port it came in on If unicast MAC address is in MAC address table, send it out only that port If unicast MAC address is not in in MAC address table, flood out all ports except the port it came in on (unknown unicast) S1 can now forward the frame by examining the destination MAC address The destination MAC address 00-0B is not in its MAC address table, so it floods it out all ports This is known as an unknown unicast

S1 MAC Address Table S2 MAC Address Table Port MAC Address Port MAC Address Internet 1 00-0A S1 1 2 3 4 S2 1 2 3 4 Router 1 2 MAC 00-0D A B C MAC 00-0A MAC 00-0B MAC 00-0C Destination MAC 00-0B Source MAC 00-0A Type Data FCS Step 2: Forwarding the frame (Using the MAC address table) Switch forwards by examining the destination MAC address If broadcast/multicast MAC address, flood out all ports except the port it came in on If unicast MAC address is in MAC address table, send it out only that port If unicast MAC address is not in in MAC address table, flood out all ports except the port it came in on (unknown unicast) PC-B’s NIC receives the frame. After comparing the destination MAC address of 00-0B to it own NIC’s MAC address it realizes they are the same and copies in the rest of the frame.

S1 MAC Address Table S2 MAC Address Table Port MAC Address Port MAC Address Internet 1 00-0A 1 00-0A S1 1 2 3 4 S2 1 2 3 4 Router 1 2 MAC 00-0D A B C MAC 00-0A MAC 00-0B MAC 00-0C Destination MAC 00-0B Source MAC 00-0A Type Data FCS For every Ethernet frame that enters a port, the switch will: Step 1: Learn (Building the MAC address table) Switch learns by examining the source MAC address If not in MAC address table, then add it along with incoming port number If in MAC address table, reset 5 minute timer The frame is also flooded out S1’s port 4 which is connected to switch S2 S2 receives the frame and examines the source MAC address Since this is new information, S2 add the source MAC address 00-0A and the incoming port number 1 to its MAC address table

S1 MAC Address Table S2 MAC Address Table Port MAC Address Port MAC Address Internet 1 00-0A 1 00-0A S1 1 2 3 4 S2 1 2 3 4 Router 1 2 MAC 00-0D A B C MAC 00-0A MAC 00-0B MAC 00-0C Destination MAC 00-0B Source MAC 00-0A Type Data FCS Step 2: Forwarding the frame (Using the MAC address table) Switch forwards by examining the destination MAC address If broadcast/multicast MAC address, flood out all ports except the port it came in on If unicast MAC address is in MAC address table, send it out only that port If unicast MAC address is not in in MAC address table, flood out all ports except the port it came in on (unknown unicast) S2 can now forward the frame by examining the destination MAC address The destination MAC address 00-0B is not in its MAC address table, so it floods it out all ports Again, this is known as an unknown unicast

X X S1 MAC Address Table S2 MAC Address Table Port MAC Address Port Internet 1 00-0A 1 00-0A S1 1 2 3 4 S2 1 2 3 4 Router 1 2 X MAC 00-0D A B C X MAC 00-0A MAC 00-0B MAC 00-0C Destination MAC 00-0B Source MAC 00-0A Type Data FCS Step 2: Forwarding the frame (Using the MAC address table) Switch forwards by examining the destination MAC address If broadcast/multicast MAC address, flood out all ports except the port it came in on If unicast MAC address is in MAC address table, send it out only that port If unicast MAC address is not in in MAC address table, flood out all ports except the port it came in on (unknown unicast) Both PC-C’s NIC and the Router’s NIC receives the frame. Since their MAC addresses do not match the destination MAC address they drop the rest of the frame

S1 MAC Address Table S2 MAC Address Table Port MAC Address Port MAC Address Internet 1 00-0A 1 00-0A S1 1 2 3 4 S2 1 2 3 4 Router 1 2 MAC 00-0D A B C MAC 00-0A MAC 00-0B MAC 00-0C Destination MAC 00-0A Source MAC 00-0B Type Data FCS For every Ethernet frame that enters a port, the switch will: Step 1: Learn (Building the MAC address table) Switch learns by examining the source MAC address If not in MAC address table, then add it along with incoming port number If in MAC address table, reset 5 minute timer PC-B now sends the frame to PC-A The frame is received by switch S1

S1 MAC Address Table S2 MAC Address Table Port MAC Address Port MAC Address Internet 1 00-0A 1 00-0A 3 00-0B S1 1 2 3 4 S2 1 2 3 4 Router 1 2 MAC 00-0D A B C MAC 00-0A MAC 00-0B MAC 00-0C Destination MAC 00-0A Source MAC 00-0B Type Data FCS For every Ethernet frame that enters a port, the switch will: Step 1: Learn (Building the MAC address table) Switch learns by examining the source MAC address If not in MAC address table, then add it along with incoming port number If in MAC address table, reset 5 minute timer Switch S1 sees if it has something to learn by examining the source MAC address The source MAC address is not in its MAC address table S1 adds the source MAC address 00-0B and the incoming port 3 to its MAC address table

S1 MAC Address Table S2 MAC Address Table Port MAC Address Port MAC Address Internet 1 00-0A 1 00-0A 3 00-0B S1 1 2 3 4 S2 1 2 3 4 Router 1 2 MAC 00-0D A B C MAC 00-0A MAC 00-0B MAC 00-0C Destination MAC 00-0A Source MAC 00-0B Type Data FCS Step 2: Forwarding the frame (Using the MAC address table) Switch forwards by examining the destination MAC address If broadcast/multicast MAC address, flood out all ports except the port it came in on If unicast MAC address is in MAC address table, send it out only that port If unicast MAC address is not in in MAC address table, flood out all ports except the port it came in on (unknown unicast) S1 can now forward the frame by examining the destination MAC address The destination MAC address 00-0A is in its MAC address table, so it filters the frame by sending it out only port 1

5.2.1.5 - Sending a Frame to the Default Gateway

Destination IP address on a remote network S1 MAC Address Table S2 MAC Address Table Port MAC Address Port MAC Address 1 00-0A 1 00-0A 3 00-0B Internet S1 1 2 3 4 S2 1 2 3 4 Router 1 2 MAC 00-0D A B C MAC 00-0A MAC 00-0B MAC 00-0C Destination MAC 00-0D Source MAC 00-0A Type Data Destination IP address on a remote network FCS Destination IP address is on a remote network. PC-A will send the Ethernet frame to the MAC address of the default gateway

Destination IP address on a remote network S1 MAC Address Table S2 MAC Address Table Port MAC Address Port MAC Address 1 00-0A 1 00-0A 3 00-0B Internet S1 1 2 3 4 S2 1 2 3 4 Router 1 2 MAC 00-0D A B C MAC 00-0A MAC 00-0B MAC 00-0C Destination MAC 00-0D Source MAC 00-0A Type Data Destination IP address on a remote network FCS For every Ethernet frame that enters a port, the switch will: Step 1: Learn (Building the MAC address table) Switch learns by examining the source MAC address If not in MAC address table, then add it along with incoming port number If in MAC address table, reset 5 minute timer Switch S1 sees if it has something to learn by examining the source MAC address The source MAC address is in its MAC address table, so it has nothing new to learn S1 refreshes the 5 minute refresh timer for this entry

Destination IP address on a remote network S1 MAC Address Table S2 MAC Address Table Port MAC Address Port MAC Address 1 00-0A 1 00-0A 3 00-0B Internet S1 1 2 3 4 S2 1 2 3 4 Router 1 2 MAC 00-0D A B C MAC 00-0A MAC 00-0B MAC 00-0C Destination MAC 00-0D Source MAC 00-0A Type Data Destination IP address on a remote network FCS Step 2: Forwarding the frame (Using the MAC address table) Switch forwards by examining the destination MAC address If broadcast/multicast MAC address, flood out all ports except the port it came in on If unicast MAC address is in MAC address table, send it out only that port If unicast MAC address is not in in MAC address table, flood out all ports except the port it came in on (unknown unicast) S1 can now forward the frame by examining the destination MAC address The destination MAC address 00-0D is not in its MAC address table, so it floods it out all ports This is known as an unknown unicast

Destination IP address on a remote network S1 MAC Address Table S2 MAC Address Table Port MAC Address Port MAC Address 1 00-0A 1 00-0A 3 00-0B Internet S1 1 2 3 4 S2 1 2 3 4 Router 1 2 MAC 00-0D X A B C MAC 00-0A MAC 00-0B MAC 00-0C Destination MAC 00-0D Source MAC 00-0A Type Data Destination IP address on a remote network FCS Step 2: Forwarding the frame (Using the MAC address table) Switch forwards by examining the destination MAC address If broadcast/multicast MAC address, flood out all ports except the port it came in on If unicast MAC address is in MAC address table, send it out only that port If unicast MAC address is not in in MAC address table, flood out all ports except the port it came in on (unknown unicast) PC-B’s NIC receives the frame and ignores the rest of the frame after determining that the destination MAC address of 00-0D does not match it’s own MAC address of 00-0B

Destination IP address on a remote network S1 MAC Address Table S2 MAC Address Table Port MAC Address Port MAC Address 1 00-0A 1 00-0A 3 00-0B Internet S1 1 2 3 4 S2 1 2 3 4 Router 1 2 MAC 00-0D X A B C MAC 00-0A MAC 00-0B MAC 00-0C Destination MAC 00-0D Source MAC 00-0A Type Data Destination IP address on a remote network FCS For every Ethernet frame that enters a port, the switch will: Step 1: Learn (Building the MAC address table) Switch learns by examining the source MAC address If not in MAC address table, then add it along with incoming port number If in MAC address table, reset 5 minute timer The frame is also flooded out S1’s port 4 which is connected to switch S2 S2 receives the frame and examines the source MAC address The source MAC address of 00-0A and port 1 is in its MAC address table, so it has nothing new to learn S2 refreshes the 5 minute refresh timer for this entry

Destination IP address on a remote network S1 MAC Address Table S2 MAC Address Table Port MAC Address Port MAC Address 1 00-0A 1 00-0A 3 00-0B Internet S1 1 2 3 4 S2 1 2 3 4 Router 1 2 MAC 00-0D X A B C MAC 00-0A MAC 00-0B MAC 00-0C Destination MAC 00-0D Source MAC 00-0A Type Data Destination IP address on a remote network FCS Step 2: Forwarding the frame (Using the MAC address table) Switch forwards by examining the destination MAC address If broadcast/multicast MAC address, flood out all ports except the port it came in on If unicast MAC address is in MAC address table, send it out only that port If unicast MAC address is not in in MAC address table, flood out all ports except the port it came in on (unknown unicast) S2 can now forward the frame by examining the destination MAC address The destination MAC address 00-0D is not in its MAC address table, so it floods it out all ports Again, this is known as an unknown unicast

Destination IP address on a remote network S1 MAC Address Table S2 MAC Address Table Port MAC Address Port MAC Address 1 00-0A 1 00-0A 3 00-0B Internet S1 1 2 3 4 S2 1 2 3 4 Router 1 2 MAC 00-0D X X A B C MAC 00-0A MAC 00-0B MAC 00-0C Destination MAC 00-0D Source MAC 00-0A Type Data Destination IP address on a remote network FCS Step 2: Forwarding the frame (Using the MAC address table) Switch forwards by examining the destination MAC address If broadcast/multicast MAC address, flood out all ports except the port it came in on If unicast MAC address is in MAC address table, send it out only that port If unicast MAC address is not in in MAC address table, flood out all ports except the port it came in on (unknown unicast) PC-C’s NIC and the Router’s NIC receives the frame. PC-C’s MAC addresses does not match the destination MAC address so it drops the rest of the frame The router’s MAC address does match the destination MAC address so it copies in the rest of the frame The router will de-encapsulate the data from the Ethernet frame and process the Layer 3 PDU, the IP packet, for routing.

Source IP address on a remote network S1 MAC Address Table S2 MAC Address Table Port MAC Address Port MAC Address 1 00-0A 1 00-0A 3 00-0B Internet S1 1 2 3 4 S2 1 2 3 4 Router 1 2 MAC 00-0D A B C MAC 00-0A MAC 00-0B MAC 00-0C Destination MAC 00-0A Source MAC 00-0D Type Data Source IP address on a remote network FCS For every Ethernet frame that enters a port, the switch will: Step 1: Learn (Building the MAC address table) Switch learns by examining the source MAC address If not in MAC address table, then add it along with incoming port number If in MAC address table, reset 5 minute timer The router now sends the frame to PC-A The frame is received by switch S2

Source IP address on a remote network S1 MAC Address Table S2 MAC Address Table Port MAC Address Port MAC Address 1 00-0A 1 00-0A 3 00-0B 4 00-0D Internet S1 1 2 3 4 S2 1 2 3 4 Router 1 2 MAC 00-0D A B C MAC 00-0A MAC 00-0B MAC 00-0C Destination MAC 00-0A Source MAC 00-0D Type Data Source IP address on a remote network FCS For every Ethernet frame that enters a port, the switch will: Step 1: Learn (Building the MAC address table) Switch learns by examining the source MAC address If not in MAC address table, then add it along with incoming port number If in MAC address table, reset 5 minute timer Switch S2 sees if it has something to learn by examining the source MAC address The source MAC address is not in its MAC address table S2 adds the source MAC address 00-0D and the incoming port 4 to its MAC address table

Source IP address on a remote network S1 MAC Address Table S2 MAC Address Table Port MAC Address Port MAC Address 1 00-0A 1 00-0A 3 00-0B 4 00-0D Internet 4 00-0D S1 1 2 3 4 S2 1 2 3 4 Router 1 2 MAC 00-0D A B C MAC 00-0A MAC 00-0B MAC 00-0C Destination MAC 00-0A Source MAC 00-0D Type Data Source IP address on a remote network FCS Step 2: Forwarding the frame (Using the MAC address table) Switch forwards by examining the destination MAC address If broadcast/multicast MAC address, flood out all ports except the port it came in on If unicast MAC address is in MAC address table, send it out only that port If unicast MAC address is not in in MAC address table, flood out all ports except the port it came in on (unknown unicast) S2 can now forward the frame by examining the destination MAC address The destination MAC address 00-0A is in its MAC address table, so it filters the frame by sending it out only port 1

Source IP address on a remote network S1 MAC Address Table S2 MAC Address Table Port MAC Address Port MAC Address 1 00-0A 1 00-0A 3 00-0B 4 00-0D Internet 4 00-0D S1 1 2 3 4 S2 1 2 3 4 Router 1 2 MAC 00-0D A B C MAC 00-0A MAC 00-0B MAC 00-0C Destination MAC 00-0A Source MAC 00-0D Type Data Source IP address on a remote network FCS For every Ethernet frame that enters a port, the switch will: Step 1: Learn (Building the MAC address table) Switch learns by examining the source MAC address If not in MAC address table, then add it along with incoming port number If in MAC address table, reset 5 minute timer Switch S1 sees if it has something to learn by examining the source MAC address The source MAC address is in its MAC address table, so it has nothing new to learn S1 refreshes the 5 minute refresh timer for this entry

Source IP address on a remote network S1 MAC Address Table S2 MAC Address Table Port MAC Address Port MAC Address 1 00-0A 1 00-0A 3 00-0B 4 00-0D Internet 4 00-0D S1 1 2 3 4 S2 1 2 3 4 Router 1 2 MAC 00-0D A B C MAC 00-0A MAC 00-0B MAC 00-0C Destination MAC 00-0A Source MAC 00-0D Type Data Source IP address on a remote network FCS Step 2: Forwarding the frame (Using the MAC address table) Switch forwards by examining the destination MAC address If broadcast/multicast MAC address, flood out all ports except the port it came in on If unicast MAC address is in MAC address table, send it out only that port If unicast MAC address is not in in MAC address table, flood out all ports except the port it came in on (unknown unicast) S1 can now forward the frame by examining the destination MAC address The destination MAC address 00-0A is in its MAC address table, so it filters the frame by sending it out only port 1

5.3.2.3 - ARP Operation - ARP Request

B A C Internet R1 IP Packet Source IP 192.168.1.110 Destination IP 192.168.1.120 MAC 00-0B B A C 192.168.1.50 MAC 00-0C 192.168.1.110 MAC 00-0A 192.168.1.1 MAC 00-0D Internet R1 IP Packet PCA at 192.168.1.110 has an IPv4 packet to send to 192.168.1.50 Comparing its IPv4 address with the destination IPv4 address, PCA determines this device is on the same IP network Ethernet Header Destination MAC ??? Source MAC 00-0A Source IP 192.168.1.110 Destination IP 192.168.1.50

IPv4 Address MAC Address 192.168.1.120 MAC 00-0B B PC-A’s ARP Cache IPv4 Address MAC Address A C 192.168.1.50 MAC 00-0C 192.168.1.110 MAC 00-0A 192.168.1.1 MAC 00-0D Internet R1 IP Packet PCA checks its ARP table for 192.168.1.50 but no match Ethernet Header Destination MAC ??? Source MAC 00-0A Source IP 192.168.1.110 Destination IP 192.168.1.50

IPv4 Address MAC Address 192.168.1.120 MAC 00-0B B PC-A’s ARP Cache IPv4 Address MAC Address A C 192.168.1.50 MAC 00-0C 192.168.1.110 MAC 00-0A 192.168.1.1 MAC 00-0D Internet R1 Ethernet Header ARP Request Destination MAC FF-FF Source MAC 00-0A Target IPv4 192.168.1.50 Target MAC ??? PCA puts the IPv4 packet on hold and creates an ARP Request with Target IPv4 = 192.168.1.50 Target MAC – unknown Source MAC 00-A Destination MAC = broadcast Ethernet Header IP Packet On Hold Destination MAC ??? Source MAC 00-0A Source IP 192.168.1.110 Destination IP 192.168.1.50

IPv4 Address MAC Address 192.168.1.120 MAC 00-0B B PC-A’s ARP Cache IPv4 Address MAC Address A C 192.168.1.50 MAC 00-0C 192.168.1.110 MAC 00-0A 192.168.1.1 MAC 00-0D Internet R1 Ethernet Header ARP Request Destination MAC FF-FF Source MAC 00-0A Target IPv4 192.168.1.50 Target MAC ??? PCA sends the ARP request which is received by the switch Because the destination MAC is a broadcast the switch sends it out all ports but the incoming port Ethernet Header IP Packet On Hold Destination MAC ??? Source MAC 00-0A Source IP 192.168.1.110 Destination IP 192.168.1.50

IPv4 Address MAC Address The target IPv4 is not me. 192.168.1.120 MAC 00-0B B PC-A’s ARP Cache IPv4 Address MAC Address A C 192.168.1.50 MAC 00-0C 192.168.1.110 MAC 00-0A 192.168.1.1 MAC 00-0D Internet R1 Ethernet Header ARP Request Destination MAC FF-FF Source MAC 00-0A Target IPv4 192.168.1.50 Target MAC ??? PCB compares the target IPv4 address to its own MAC address and because it is not a match ignores the ARP request Ethernet Header IP Packet On Hold Destination MAC ??? Source MAC 00-0A Source IP 192.168.1.110 Destination IP 192.168.1.50

IPv4 Address MAC Address 192.168.1.120 MAC 00-0B B PC-A’s ARP Cache IPv4 Address MAC Address A C 192.168.1.50 MAC 00-0C 192.168.1.110 MAC 00-0A 192.168.1.1 MAC 00-0D The target IPv4 is not me. Internet R1 Ethernet Header ARP Request Destination MAC FF-FF Source MAC 00-0A Target IPv4 192.168.1.50 Target MAC ??? Router R1 compares the target IPv4 address to its own MAC address and because it is not a match ignores the ARP request. Routers do not forward broadcasts. Ethernet Header IP Packet On Hold Destination MAC ??? Source MAC 00-0A Source IP 192.168.1.110 Destination IP 192.168.1.50

IPv4 Address MAC Address 192.168.1.120 MAC 00-0B The target IPv4 is me! B PC-A’s ARP Cache IPv4 Address MAC Address A C 192.168.1.50 MAC 00-0C 192.168.1.110 MAC 00-0A 192.168.1.1 MAC 00-0D Internet R1 Ethernet Header ARP Request Destination MAC FF-FF Source MAC 00-0A Target IPv4 192.168.1.50 Target MAC ??? The target address in the ARP request matches PCC’s IPv4 address Ethernet Header IP Packet On Hold Destination MAC ??? Source MAC 00-0A Source IP 192.168.1.110 Destination IP 192.168.1.50

5.3.2.4 - ARP Operation - ARP Reply

IPv4 Address MAC Address 192.168.1.120 MAC 00-0B The target IPv4 is me! B PC-A’s ARP Cache IPv4 Address MAC Address A C 192.168.1.50 MAC 00-0C 192.168.1.110 MAC 00-0A 192.168.1.1 MAC 00-0D Internet R1 Ethernet Header ARP Request Destination MAC FF-FF Source MAC 00-0A Target IPv4 192.168.1.50 Target MAC ??? The target address in the ARP request matches PCC’s IPv4 address Ethernet Header IP Packet On Hold Destination MAC ??? Source MAC 00-0A Source IP 192.168.1.110 Destination IP 192.168.1.50

Here is my MAC address for the IPv4 address you were looking for! 192.168.1.120 MAC 00-0B B PC-A’s ARP Cache IPv4 Address MAC Address A C 192.168.1.50 MAC 00-0C 192.168.1.110 MAC 00-0A 192.168.1.1 MAC 00-0D Internet R1 Ethernet Header ARP Reply Destination MAC 00-0A Source MAC 00-0C Sender IPv4 192.168.1.50 Sender MAC 00-0C PCC sends an ARP reply to the sender of the ARP request This is a unicast Sender IPv4 = 192.168.1.50 Sender MAC – 00-0C Source MAC 00-0C Destination MAC = 00-0A Ethernet Header IP Packet On Hold Destination MAC ??? Source MAC 00-0A Source IP 192.168.1.110 Destination IP 192.168.1.50

Here is my MAC address for the IPv4 address you were looking for! 192.168.1.120 MAC 00-0B B PC-A’s ARP Cache IPv4 Address MAC Address A C 192.168.1.50 MAC 00-0C 192.168.1.110 MAC 00-0A 192.168.1.1 MAC 00-0D Internet R1 Ethernet Header ARP Reply Destination MAC 00-0A Source MAC 00-0C Sender IPv4 192.168.1.50 Sender MAC 00-0C PCA receives the ARP reply Ethernet Header IP Packet On Hold Destination MAC ??? Source MAC 00-0A Source IP 192.168.1.110 Destination IP 192.168.1.50

IPv4 Address MAC Address 192.168.1.120 MAC 00-0B B PC-A’s ARP Cache IPv4 Address MAC Address 192.168.1.50 00-0C A C 192.168.1.50 MAC 00-0C 192.168.1.110 MAC 00-0A 192.168.1.1 MAC 00-0D Internet R1 Ethernet Header ARP Reply Destination MAC 00-0A Source MAC 00-0C Sender IPv4 192.168.1.50 Sender MAC 00-0C PCC Adds the sender’s IPv4 address and MAC address to its ARP table Ethernet Header IP Packet On Hold Destination MAC ??? Source MAC 00-0A Source IP 192.168.1.110 Destination IP 192.168.1.50

IPv4 Address MAC Address 192.168.1.120 MAC 00-0B B PC-A’s ARP Cache IPv4 Address MAC Address 192.168.1.50 00-0C A C 192.168.1.50 MAC 00-0C 192.168.1.110 MAC 00-0A 192.168.1.1 MAC 00-0D Internet R1 PCC takes the IPv4 packet off hold PCC uses the MAC address for the destination MAC address Ethernet Header IP Packet Destination MAC ??? Source MAC 00-0A Source IP 192.168.1.110 Destination IP 192.168.1.50

IPv4 Address MAC Address 192.168.1.120 MAC 00-0B B PC-A’s ARP Cache IPv4 Address MAC Address 192.168.1.50 00-0C A C 192.168.1.50 MAC 00-0C 192.168.1.110 MAC 00-0A 192.168.1.1 MAC 00-0D Internet R1 PCA now sends this Ethernet frame with the encapsulated IPv4 packet out its Ethernet NIC Ethernet Header IP Packet Destination MAC 00-0C Source MAC 00-0A Source IP 192.168.1.110 Destination IP 192.168.1.50

5.3.2.5 - ARP Role in Remote Communication

B A C Internet R1 IP Packet Source IP 192.168.1.110 Destination IP 192.168.1.120 MAC 00-0B B A C 192.168.1.50 MAC 00-0C 192.168.1.110 MAC 00-0A 192.168.1.1 MAC 00-0D Default Gateway: 192.168.1.1 Internet R1 PCA at 192.168.1.110 has an IPv4 packet to send to 10.1.1.10 Comparing its IPv4 address with the destination IPv4 address, PCA determines this device is on a different IP network PCA must sent this packet to its default gateway 192.168.1.1 Ethernet Header IP Packet Destination MAC ??? Source MAC 00-0A Source IP 192.168.1.110 Destination IP 10.1.1.10

IPv4 Address MAC Address 192.168.1.120 MAC 00-0B B PC-A’s ARP Cache IPv4 Address MAC Address A C 192.168.1.50 MAC 00-0C 192.168.1.110 MAC 00-0A 192.168.1.1 MAC 00-0D Default Gateway: 192.168.1.1 Internet R1 PCA checks its ARP table for 192.168.1.1 but no match Ethernet Header IP Packet Destination MAC ??? Source MAC 00-0A Source IP 192.168.1.110 Destination IP 10.1.1.10

IPv4 Address MAC Address 192.168.1.120 MAC 00-0B B PC-A’s ARP Cache IPv4 Address MAC Address A C 192.168.1.50 MAC 00-0C 192.168.1.110 MAC 00-0A 192.168.1.1 MAC 00-0D Default Gateway: 192.168.1.1 Internet R1 Ethernet Header ARP Request Destination MAC FF-FF Source MAC 00-0A Target IPv4 192.168.1.1 Target MAC ??? PCA puts the IPv4 packet on hold and creates an ARP Request with Target IPv4 = 192.168.1.1 Target MAC – unknown Source MAC 00-A Destination MAC = broadcast Ethernet Header IP Packet On Hold Destination MAC ??? Source MAC 00-0A Source IP 192.168.1.110 Destination IP 10.1.1.10

IPv4 Address MAC Address 192.168.1.120 MAC 00-0B B PC-A’s ARP Cache IPv4 Address MAC Address A C 192.168.1.50 MAC 00-0C 192.168.1.110 MAC 00-0A 192.168.1.1 MAC 00-0D Default Gateway: 192.168.1.1 Internet R1 Ethernet Header ARP Request Destination MAC FF-FF Source MAC 00-0A Target IPv4 192.168.1.1 Target MAC ??? PCA sends the ARP request which is received by the switch Because the destination MAC is a broadcast the switch sends it out all ports but the incoming port Ethernet Header IP Packet On Hold Destination MAC ??? Source MAC 00-0A Source IP 192.168.1.110 Destination IP 10.1.1.10

IPv4 Address MAC Address The target IPv4 is not me. 192.168.1.120 MAC 00-0B B PC-A’s ARP Cache IPv4 Address MAC Address A C 192.168.1.50 MAC 00-0C 192.168.1.110 MAC 00-0A 192.168.1.1 MAC 00-0D Default Gateway: 192.168.1.1 Internet R1 Ethernet Header ARP Request Destination MAC FF-FF Source MAC 00-0A Target IPv4 192.168.1.1 Target MAC ??? PCB compares the target IPv4 address to its own MAC address and because it is not a match ignores the ARP request Ethernet Header IP Packet On Hold Destination MAC ??? Source MAC 00-0A Source IP 192.168.1.110 Destination IP 10.1.1.10

IPv4 Address MAC Address 192.168.1.120 MAC 00-0B B PC-A’s ARP Cache IPv4 Address MAC Address The target IPv4 is not me. A C 192.168.1.50 MAC 00-0C 192.168.1.110 MAC 00-0A 192.168.1.1 MAC 00-0D Default Gateway: 192.168.1.1 Internet R1 Ethernet Header ARP Request Destination MAC FF-FF Source MAC 00-0A Target IPv4 192.168.1.1 Target MAC ??? PCC compares the target IPv4 address to its own MAC address and because it is not a match ignores the ARP request Ethernet Header IP Packet On Hold Destination MAC ??? Source MAC 00-0A Source IP 192.168.1.110 Destination IP 10.1.1.10

IPv4 Address MAC Address 192.168.1.120 MAC 00-0B B PC-A’s ARP Cache IPv4 Address MAC Address A C The target IPv4 is for me! 192.168.1.50 MAC 00-0C 192.168.1.110 MAC 00-0A 192.168.1.1 MAC 00-0D Default Gateway: 192.168.1.1 Internet R1 Ethernet Header ARP Request Destination MAC FF-FF Source MAC 00-0A Target IPv4 192.168.1.1 Target MAC ??? The target address in the ARP request matches the router’s the IPv4 address on its G0/0 interface Ethernet Header IP Packet On Hold Destination MAC ??? Source MAC 00-0A Source IP 192.168.1.110 Destination IP 10.1.1.10

IPv4 Address MAC Address 192.168.1.120 MAC 00-0B B PC-A’s ARP Cache IPv4 Address MAC Address A C 192.168.1.50 MAC 00-0C 192.168.1.110 MAC 00-0A Here is my MAC address for the IPv4 address you were looking for! 192.168.1.1 MAC 00-0D Default Gateway: 192.168.1.1 Internet R1 Ethernet Header ARP Reply Destination MAC 00-0A Source MAC 00-0D Target IPv4 192.168.1.1 Target MAC 00-0D PCC sends an ARP reply to the sender of the ARP request This is a unicast Sender IPv4 = 192.168.1.1 Sender MAC – 00-0D Source MAC 00-0D Destination MAC = 00-0A Ethernet Header IP Packet On Hold Destination MAC ??? Source MAC 00-0A Source IP 192.168.1.110 Destination IP 10.1.1.10

IPv4 Address MAC Address 192.168.1.120 MAC 00-0B B PC-A’s ARP Cache IPv4 Address MAC Address A C 192.168.1.50 MAC 00-0C 192.168.1.110 MAC 00-0A 192.168.1.1 MAC 00-0D Default Gateway: 192.168.1.1 Internet R1 Ethernet Header ARP Reply Destination MAC 00-0A Source MAC 00-0D Target IPv4 192.168.1.1 Target MAC 00-0D PCA receives the ARP reply Ethernet Header IP Packet On Hold Destination MAC ??? Source MAC 00-0A Source IP 192.168.1.110 Destination IP 10.1.1.10

IPv4 Address MAC Address 192.168.1.120 MAC 00-0B B PC-A’s ARP Cache IPv4 Address MAC Address 192.168.1.1 00-0D A C 192.168.1.50 MAC 00-0C 192.168.1.110 MAC 00-0A 192.168.1.1 MAC 00-0D Default Gateway: 192.168.1.1 Internet R1 Ethernet Header ARP Reply Destination MAC 00-00A Source MAC 00-0D Target IPv4 192.168.1.1 Target MAC 00-0D PCC Adds the sender’s IPv4 address and MAC address to its ARP table Ethernet Header IP Packet On Hold Destination MAC ??? Source MAC 00-0A Source IP 192.168.1.110 Destination IP 10.1.1.10

IPv4 Address MAC Address 192.168.1.120 MAC 00-0B B PC-A’s ARP Cache IPv4 Address MAC Address 192.168.1.1 00-0D A C 192.168.1.50 MAC 00-0C 192.168.1.110 MAC 00-0A 192.168.1.1 MAC 00-0D Default Gateway: 192.168.1.1 Internet R1 PCC takes the IPv4 packet off hold PCC uses the MAC address for the destination MAC address Ethernet Header IP Packet Destination MAC ??? Source MAC 00-0A Source IP 192.168.1.110 Destination IP 10.1.1.10

IPv4 Address MAC Address 192.168.1.120 MAC 00-0B B PC-A’s ARP Cache IPv4 Address MAC Address 192.168.1.1 00-0D A C 192.168.1.50 MAC 00-0C 192.168.1.110 MAC 00-0A 192.168.1.1 MAC 00-0D Default Gateway: 192.168.1.1 Internet R1 PCA now sends this Ethernet frame with the encapsulated IPv4 packet out its Ethernet NIC towards the default gateway Ethernet Header IP Packet Destination MAC 00-0D Source MAC 00-0A Source IP 192.168.1.110 Destination IP 10.1.1.10