and now we see the BIG picture. U have a core switch handling the main internet connection, and when it failed, Switch 5, which has a backup internet link, had to take over. This is an excellent question about building redundancy and resilience into a network.
The core issue here is one of dynamic path selection. U client devices point to their default gateway ( L3-SW1 for VLAN 10), but those Layer 3 switches need to know how to find the internet themselves. When their primary path vanished, they had no automatic mechanism to switch to the backup path via Switch 5. The most effective and common way to solve this is by using a floating static route. This is a brilliant feature that allows u to configure a backup route that remains dormant until the primary route fails. It's perfect for this scenario and works excellently in Packet Tracer.
The concept relies on a value called Administrative Distance (AD). This is a measure of a route's trustworthiness. A lower AD is preferred. A directly connected network has an AD of 0, a static route has an AD of 1, and we can manually configure a static route with a higher AD (like 5 or 200) to make it a backup. Here is how you would implement this solution on your Layer 3 switches, L3-SW1 and L3-SW2.
layer 3sw1 layer3 sw2:
U would log into each of your distribution layer switches (L3-SW1 and L3-SW2) and enter the following commands. Let's assume the Core Switch's IP address is 192.168.1.1 and Switch 5's IP address is 192.168.1.5. These addresses would be on a shared network segment, perhaps a dedicated VLAN for switch management and routing.
and dont forget that this is the primary default route pointing to the Core Switch.
It uses the default Administrative Distance of 1, making it the most preferred path.
ip route 0.0.0.0 0.0.0.0 192.168.1.1
now this is the backup floating static route pointing to switch5
the administrative distance of 5 makes it less trusted than the primary route.
It will only appear in the routing table if the primary route fails.
ip route 0.0.0.0 0.0.0.0 192.168.1.5 5
and why this works great! Because under normal conditions L3-SW1 sends all internet traffic to the Core Switch (next-hop 192.168.1.1). If the Core Switch link fails, L3-SW1 automatically switches to the backup floating static route (next-hop 192.168.1.5). When the Core Switch comes back online, traffic automatically returns to the primary route. This setup ensures seamless failover without manual intervention.
NOW ALL U HAVE TO DO IS TAKE THE NETWORK TOPOLOGY THAT I DID FOR U, AND ADD THE OTHER PART OF THE CORE SWITCH, AND ADD THE CONFIGS THAT I TOLD U, AND ULL BE GOOD.
thats all from me today my Cisco friend, will enjoy some sunlight after a veryy veryy veryy looooooong week.
Im out!
-Enes
more Cisco?!
more Gym?!
If this post solved your problem, kindly mark it as Accepted Solution. Much appreciated!
