Network Devices

Cisco Devices

Modes:

• > User (basic access)
• # Priviledged (run show commands)
• (config)# (config changes)

• Device configuration such as hostname is stored in running config
• To save, "copy running-config startup-config"

ICMP PDU (Ping Simulation)

PC (Office Admin) > SW (Office SW1) > Printer0

1. Last: (Blank), At: Office-Admin (ICMP)

• Outbound:
  • Layer 3:
    • ICMP echo request 
    • Source IP = unspecified, device sets to port's IP
    • Destination IP in same subnet, device sets next hop to destination IP
  • Layer 2:
    • Next hop = unicast, looks it up in ARP table
    • Found in ARP, ARP process sets frame destination accordingly
  • Layer 1:
    • FastEthernet0 sends the Frame

2. Last: Office-Admin, At: Office-SW1 (ICMP)

• Inbound:
  • Layer 1:
    • Receives Frame
  • Layer 2:
    • Frame source MAC address not in MAC table, adds it
    • (Unicast Frame) look up Destination MAC address in MAC table
• Outbound:
  • Layer 2:
    • Not in table, Floods frame to all ports in VLAN except inbound
  • Layer 1:
    • Ports 1, 2, 3, 4, 5, 6 send Frame

3. Last: Office-SW1, At: Office-R1 (ICMP)

• Inbound:
  • Layer 1:
    • Receives Frame on G0/0/0
  • Layer 2:
    • Subinterface G0/0/0.20 accepts from this VLAN
    • Frame destination MAC does not match receiving port's MAC
    • Drops the Frame

4. Last: Office-SW1, At: Printer0 (ICMP)

• Inbund:
  • Layer 1:
    • Receives Frame on FE0
  • Layer 2:
    • Frame Destination MAC = receiving port's MAC
    • De-capsulate PDU from the Frame
  • Layer 3:
    • Packet Destination IP = Device Destination IP
    • De-capsulate Packet, identifies ICMP, processes it
    • Identifies as Echo request message
• Outbound:
  • Layer 3:
    • ICMP process sends Echo reply
    • Destination IP = same subnet, sets next hop to Destination IP
  • Layer 2:
    • Next hop = unicast, looks it up in ARP table
    • Found in ARP, ARP sets Frame desination MAC to the same
    • Encapsulates PDU into Frame
  • Layer 1:
    • FE0 sends Frame

5. Last: Printer0, At: Office-SW1 (ICMP)

• Inbound:
  • Layer 1:
    • GE1/0/17 Receives Frame
  • Layer 2:
    • Frame source MAC is not in MAC table, adds it
    • Unicast Frame, looks up destination MAC in table
• Outbound:
  • Layer 2:
    • Outgoing port = access port
    • Switch sends the frame out of that port
  • Layer 1:
    • GE1/0/19 sends the Frame

6. Last: Office-SW1, At: Office-Admin (ICMP)

• Inbound: 
  • Layer 1: FE0 Receives Frame
  • Layer 2:
    • Frame destination MAC = Receiving port MAC
    • Decapsulates Frame
  • Layer 3:
    • Packet destination IP = device IP
    • decapsulates Packet
    • Identifies ICMP Packet
    • ICMP process received Echo reply message