Dascalu Stefan-Nicolae

Switch Implementation

Task 1: MAC Learning and Forwarding

In the first task, the switch was built to handle MAC address learning, enabling efficient packet forwarding.

Features

1. MAC Table Initialization

   • A dictionary mac_table stores mappings between MAC addresses and their corresponding interfaces.

2. Frame Reception

   • Upon receiving a frame on an interface, the switch extracts the source and destination MAC addresses from the Ethernet header.

3. MAC Learning

   • The switch learns the source MAC address by adding it to mac_table with the interface it arrived on. This learning process allows the switch to determine where to send frames for known MAC addresses.

4. Forwarding Logic

   • Unicast Frames
     • If the destination MAC address is in mac_table, the frame is forwarded to the associated interface.
     • If the destination MAC address is not in mac_table, the frame is broadcasted to all other interfaces except the incoming one.
   • Broadcast/Multicast Frames
     • The frame is forwarded to all interfaces except the one it arrived on.
   • Unicast Check
     • A helper function, is_unicast, checks if the destination MAC address is a unicast address by verifying it is not the broadcast address (ff:ff:ff:ff:ff:ff).

Task 2: VLAN Support

In the second task, VLAN support was added to enable network segmentation at the data link layer.

VLAN Implementation

1. VLAN Table Initialization

   • A vlan_table dictionary stores VLAN configurations for each interface.
   • The parse_config function reads VLAN configurations from files located in the configs directory. These files specify VLAN IDs for each interface or mark them as trunk ports (which carry traffic for multiple VLANs).

2. Reading Configuration Files

   • The switch reads its configuration file (e.g., switch0.cfg) based on its ID.
   • Each line after the first (priority line, unused in this task) contains the interface name and its VLAN ID or T to indicate a trunk port.
   • VLAN IDs are stored in vlan_table, with trunk ports assigned a VLAN ID of -1.

3. Frame Processing with VLANs

   • VLAN ID Determination
     • Trunk Ports: Extract the VLAN ID from the VLAN tag in the frame header, then remove the tag.
     • Access Ports: Obtain the VLAN ID from vlan_table using the interface.

4. Forwarding with VLAN Consideration

   • The switch updates mac_table to associate MAC addresses with both the interface and VLAN ID.
   • Frames are forwarded only to interfaces that belong to the same VLAN or are trunk ports.
   • VLAN checks are applied before forwarding to ensure that frames are restricted to the correct VLAN.

5. VLAN Tagging and Untagging

   • Adding VLAN Tags: VLAN tags are added to frames forwarded to trunk ports.
   • Removing VLAN Tags: VLAN tags are removed when frames are forwarded to access ports.

6. Updating Forwarding Logic

   • The forwarding function was enhanced to consider VLAN IDs in addition to MAC addresses.
   • The switch checks both the MAC address and VLAN ID during forwarding.

7. Handling Interface Types

   • Trunk Ports: Use the VLAN ID from the frame’s VLAN tag.
   • Access Ports: Use the VLAN ID assigned to the interface in vlan_table.