EIGRP load balancing
1.3.d i Equal-cost
General information on “EIGRP equal-cost load balancing”:
- Only Feasible Successor routes are considered for load balancing
- If two or more paths to the same destination network have the same metric, they will both be installed in the routing table
- These paths will be used for load balancing the traffic
- By default, 4 paths will be installed
- This can be modified up to 32 paths
- This can also be disabled by changing the maximum-paths value to 1
“EIGRP Equal-cost load balacing” CLI configuration commands:
## Configuring EIGRP equal-cost load balacing (classic mode)
Router(config)# router eigrp <asn>
Router(config-router)# maximum-paths <number>
## Configuring EIGRP equal-cost load balacing (named mode)
Router(config-router-af)# topology base
Router(config-router-af-topology)# maximum-paths <number>
“EIGRP Equal-cost load balacing” CLI show commands:
## Showing the EIGRP topology table
Router# show [ip | ipv6] eigrp topology
## Showing the global routing table
Router# show [ip | ipv6] route
## Showing the EIGRP process details
Router# show [ip | ipv6] protocols
1.3.d ii Unequal-cost
General information on “EIGRP unequal-cost load-balancing”:
- Only Feasible Successor routes are considered for load balancing
- Unequal cost load balancing is disabled by default
- If enabled, a variance multiplier will be used for route consideration
- The variance multiplier can be anything between 1 - 128
- The load will be shared based on the ratio of the variance
- Example: If the successor route has CD of 25 and the variance multiplier is configured to 10, the feasible successor route can be up to 250 (=25*10) to be installed in the routing table.
“EIGRP Unequal-cost” CLI configuration commands:
## Configuring EIGRP unequal-cost load balacing (classic mode)
Router(config)# router eigrp <asn>
Router(config-router)# variance <number>
## Configuring EIGRP unequal-cost load balacing (named mode)
Router(config-router-af)# topology base
Router(config-router-af-topology)# variance <number>
“EIGRP Unequal-cost” CLI show commands:
## Showing the EIGRP topology table
Router# show [ip | ipv6] eigrp topology
## Showing the global routing table
Router# show [ip | ipv6] route
## Showing the EIGRP process details
Router# show [ip | ipv6] protocols
1.3.d iii Add-path
General information on “EIGRP Add-path”:
- Needed for DMVPN when multiple spokes advertise the same subnet
- With EIGRP add-path the DMVPN hub can advertise all possible paths to the same destination so that all neighbors can either send traffic on both links and/or have the redundant path in the routing table for immediate failover
- Only available in EIGRP named mode
- Important: Variance and add-path is not compatible with each other and therefor variance must be set to 1!
Configuration considerations:
- Next-Hop-Self and Split-Horizon must be disabled on the DMVPN Hub in order to make add-path work
- Up to 4 additional paths can be advertised
- This means overall up to 5 paths of a specific route can be in the routing table of a Spoke (1 default + 4 additional)
- The whole configuration must be applied to the tunnel interface
“EIGRP Add-path” CLI configuration commands:
## Configuring the EIGRP add-path feature (named mode)
Router(config)# router eigrp [NAME]
Router(config-router)# address-family [ipv4 | ipv6] autonomous-system <asn>
Router(config-router-af)# af-interface [<if> | default]
Router(config-router-af-interface)# no next-hop-self no-emcp-mode
Router(config-router-af-interface)# add-path <1-4>
1.3.d Traffic share count (Not on blueprint)
General information on “EIGRP Traffic share count”:
- When using equal-cost load-balancing every link has the same traffic share (normally 1)
- When using unequal-cost load-balancing, the traffic share on multiple links differs
- This can be seen in the routing table for the specific route under traffic share count
- This can be influenced in two ways:
- Recommended: Modifying the delay value of an interface
- Not Recommended: Modifying the bandwidth of an interface