In computer networking, both routing and forwarding tables play crucial roles in packet delivery, but they serve distinct purposes. A routing table contains network path information and is maintained by routing protocols, while a forwarding table is the optimized version used by network devices to make immediate packet-forwarding decisions.

Here's a typical routing table entry in Linux:

Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
192.168.1.0     0.0.0.0         255.255.255.0   U     0      0        0 eth0
10.0.0.0        192.168.1.1     255.0.0.0       UG    100    0        0 eth0

In contrast, a forwarding table (FIB - Forwarding Information Base) has a more optimized structure:

Prefix          Next Hop        Interface      Metric
192.168.1.0/24  direct          eth0           0
10.0.0.0/8      192.168.1.1     eth0           100

The routing table is built through:

• Directly connected networks
• Static routes
• Dynamic routing protocols (OSPF, BGP, etc.)

The forwarding table is derived from the routing table but contains only the essential information needed for packet forwarding, optimized for high-speed lookup.

In Cisco IOS, you can view both tables:

# Show routing table
show ip route

# Show forwarding table
show ip cef

In Linux, the distinction is visible through:

# Routing table
ip route show

# Forwarding table (requires specific tools)
ip -d route show cache

Modern routers often implement forwarding tables using specialized hardware (TCAM) for faster lookups. Here's a simplified Python example showing how forwarding decisions might work:

def forward_packet(packet, forwarding_table):
    dest_ip = packet.destination
    # Perform longest prefix match
    best_match = None
    for prefix in forwarding_table:
        if ip_in_network(dest_ip, prefix):
            if best_match is None or prefix.prefixlen > best_match.prefixlen:
                best_match = prefix
    return forwarding_table[best_match]

At the core of network operations, routing and forwarding tables serve distinct yet complementary functions:

// Example routing table entry (Linux)
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
192.168.1.0     *              255.255.255.0   U     0      0        0 eth0
10.0.0.0        192.168.1.1    255.0.0.0       UG    100    0        0 eth0

The routing table contains network paths and maintains the "map" of the network topology, while the forwarding table contains specific instructions for packet handling at the immediate next hop.

Consider how these tables are implemented in different network devices:

# Cisco IOS forwarding table example
Switch# show mac address-table dynamic
          Mac Address Table
-------------------------------------------
Vlan    Mac Address       Type        Ports
----    -----------       --------    -----
 1      0050.0f11.2201    DYNAMIC     Fa0/1

Let's examine how to view both tables on a Linux router:

# View routing table
ip route show
# or traditional:
route -n

# View forwarding table (requires bridge-utils)
brctl showmacs br0

Modern routers optimize this separation:

// Conceptual data flow
packet -> forwarding engine (fast path)
     -> if no match -> routing engine (slow path)
     -> install new entry in forwarding table

This separation enables line-rate forwarding while maintaining flexible routing policies.