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What is ECMP Cisco?

What is ECMP Cisco?

Equal Cost Multi-Path or ECMP is a routing strategy where packets towards a single destination IP address are load-balanced over multiple best paths with equal metrics.

How does ECMP work in OSPF?

The ECMP feature allows OSPF to add routes with multiple next-hop addresses and with equal costs to a given destination in the forwarding information base (FIB) on the routing switch.

How does OSPF calculate path cost?

The Cost formula is reference bandwidth divided by interface bandwidth. The default reference bandwidth of 100 Mbps is used for OSPF cost calculation. For example, if we have an Ethernet interface (10 Mbps), the OSPF path cost value is 100 Mbps / 10 Mbps = 10.

When there are two or more routes to the same destination the route with what type of metric takes precedence?

Given two separate routes to the same destination, the router chooses the route with the lowest AD. When a router has the choice of a static route and an EIGRP route, the static route takes precedence. Similarly, a directly connected route with an AD of 0 takes precedence over a static route with an AD of 1.

Is ECMP load balancing?

Load balancing between ECMP paths is performed on IOS-XE based CEF object called loadbalance. Load balancing is a forwarding mechanism that distributes traffic over multiple links based on certain parameters. ECMP Per-Flow Load Balancing distributes packets across multiple links based on Layer 3 routing information.

What is equal and unequal load balancing?

Routes with lowest metric get installed in the routing table by default, if two or more routes having the same metric the router will install both the routes in the routing table this is called equal cost load balancing.

Is load balancing possible in BGP?

Load balancing is not possible because BGP selects only a single best path to a destination among the BGP routes that are learned from the different ASs.

How does OSPF calculate best path?

If there are multiple routes to a network with the same route type, the OSPF metric calculated as cost based on the bandwidth is used for selecting the best route. The route with the lowest value for cost is chosen as the best route.

How is path cost calculated?

SW3 receives BPDUs on its 10 Mbit interface (cost 100) and on its 1000 Mbit interface (cost 4). It will use its 1000 Mbit interface as its root port (shortest path to the root bridge is 19+19+4=42). SW3 will forward BPDUs to SW4. The root path cost field will be 100….Spanning-Tree Cost Calculation.

Bandwidth Cost
100 Mbit 19
1000 Mbit 4

What does a router do when there are two or more possible routes to the same destination?

Explanation: If there are two or more possible routes to the same destination, the metric is used to decide which route appears in the routing table.