What is the difference between the IPv4 and IPv6 routing table structures?

The IPv4 table uses a legacy classful structure with parent and child routes (inherited from classful addressing). The IPv6 table is flat and straightforward — no classful hierarchy, every route is formatted the same way.

IPv4 routing table (classful legacy structure):

     10.0.0.0/8 is variably subnetted, 5 subnets, 2 masks    ← Parent route
C       10.0.1.0/24 is directly connected, Gi0/0/0             ← Child route
L       10.0.1.1/32 is directly connected, Gi0/0/0             ← Child route
O       10.0.4.0/24 [110/50] via 10.0.3.2, Serial0/1/1        ← Child route

• Parent route: The classful network (e.g., 10.0.0.0/8 for Class A). Shown without a source code, less indented
• Child routes: Actual subnets within the classful network. Shown indented with source codes (C, L, O, S, etc.)

IPv6 routing table (flat structure):

C   2001:DB8:ACAD:1::/64 [0/0]
     via GigabitEthernet0/0/0, directly connected
L   2001:DB8:ACAD:1::1/128 [0/0]
     via GigabitEthernet0/0/0, receive
O   2001:DB8:ACAD:4::/64 [110/50]
     via FE80::2:C, Serial0/1/1

• No parent/child hierarchy — every route is a top-level entry
• Next-hop addresses for IPv6 routing protocols use link-local addresses (fe80::)
• Format is cleaner and easier to read

Why IPv4 still uses classful structure: Historical reasons — the routing table display hasn't been redesigned even though classful routing is obsolete. The lookup process itself is classless (longest prefix match), only the display uses classful grouping.

Go deeper:

• Classful network (Wikipedia) — the obsolete Class A/B/C scheme behind the IPv4 parent/child display.
• RFC 4632 — CIDR — the classless prefix/longest-match model that actually drives lookups.