Core switches can be configured with the same IP address

Core switches can share the same IP address when configured for redundancy using protocols like HSRP or VRRP, but direct IP duplication without such protocols can cause conflicts.

Using the Same IP in Redundant Setups

In high-availability networks, two core switches can be configured with the same IP address through HSRP (Hot Standby Router Protocol) or VRRP (Virtual Router Redundancy Protocol). In this setup, both switches have the same Switched Virtual Interface (SVI) IP, but one switch is designated as active and handles traffic, while the other is standby and takes over if the active switch fails. Devices on the network use the virtual IP as their default gateway, ensuring seamless failover without IP conflicts during normal operation (Cisco Community).

Key Steps: Configure the same SVI IP on both switches. Set up HSRP or VRRP with priorities to determine the active switch. Ensure connectivity between switches via a dedicated link or shared VLAN.

Configure end devices to use the virtual IP as their default gateway. Layer 2 vs Layer 3 ConsiderationsIf switches are operating purely at Layer 2, their IP addresses are primarily for management purposes.

Duplicate I

Ps on L2 switches generally do not disrupt normal traffic forwarding because Ethernet operates using MAC addresses, not IPs. However, direct management access to switches with duplicate IPs can be problematic, causing ARP table flapping or unreachable devices (ServerFault). On Layer 3 switches, IP addresses are used for routing.

Duplicate I

Ps without HSRP/VRRP will cause conflicts, making communication with those IPs unreliable. Proper configuration of unique management IPs or virtual IPs is essential to maintain network stability (ServerFault).

Risks and Best Practices

Avoid assigning the same IP to multiple switches unless using a redundancy protocol. For management purposes, ensure each switch has a unique IP to prevent conflicts. Use virtual IPs for gateways in redundant setups to provide seamless failover.

Monitor AR

P tables and network logs to detect potential IP conflicts. In summary, sharing an IP is safe and functional only in controlled redundancy scenarios like HSRP or VRRP. Outside of these protocols, duplicate IPs can lead to network instability, especially on Layer 3 networks.

Proper planning and configuration are critical to avoid conflicts while maintaining high availability.