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What is the cost of loopback interface?

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TitleWhat is the cost of loopback interface?
Question
What is the cost of loopback interface?
Environment
  • EXOS
  • OSPF
Answer
The loopback interface takes the least priority bandwidth as it doesn't do actual forwarding.
Therefore, it takes same cost value of 10Mbps interface, 10 which is the default cost of 10Mbps interface.

If OSPF metric-table configuration is set, then it also takes the configured cost value of 10Mbps interface.
For example, if you configure:

configure ospf metric-table 10M 10000 100M 1000 1G 100 10G 10 40G 2 100G 1

Then, the cost of loopback interface will be 10000 as below.

* P2.3 # sh conf ospf
#
# Module ospf configuration.
#
configure ospf routerid 4.4.4.4
configure ospf metric-table 10M 10000 100M 1000 1G 100 10G 10 40G 2 100G 1
enable ospf
configure ospf add vlan lo0 area 0.0.0.0 passive
configure ospf add vlan v102 area 0.0.0.0 link-type point-to-point
configure ospf add vlan v103 area 0.0.0.0 link-type point-to-point
configure ospf add vlan v105 area 0.0.0.0 link-type point-to-point

* P2.4 # sh ospf interfaces
 VLAN      IP Address         AREA ID         Flags      Cost State   Neighbors
lo0        4.4.4.4        /32 0.0.0.0         prif---   10000/A DR        0       
v100       100.0.0.4      /24 0.0.0.0         -r-----     100/A DOWN      0       
v102       10.0.2.2       /30 0.0.0.0         -rif---     100/A P2P       0       
v103       10.0.3.2       /30 0.0.0.0         -rif---     100/A P2P       0       
v105       10.0.5.1       /30 0.0.0.0         -rif---     100/A P2P       1       



 
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