Routing

Hey guys,

Quick question that I would try if I had a lab available to me.

Studying for the JNCIS, and had a question in regards to the reference bandwidth.

In the material it explicitly says that reference bandwidth is calculated by the physical interface's bandwidth.

But what happens when you force a physical interface to advertise at a certain speed that is slower than it's physical capabilities. 

i.e. If you configure a gigabit interface with the:

[edit]

set interface ge-0/0/0 ether-options speed 100m link-mode full-duplex

command, will OSPF see it as a 100Mb/s link or a 1Gb/s link?

Because of how it's described in the material, I'm going to go for the OSPF still seeing it as a 1Gb/s link. But maybe not 🙂

Thanks in advance,

Purplezorz

OSPF will calculate based on the interface speed (so your 100MB connection will be calculated based on it being a 100MB connection and not a 1GB connection.)

The other thing you can do is to set the bandwidth statement

set interfaces ge-0/0/1 unit 0 bandwidth 3m 

(sets the interface to 3Mb/s)

this will allow you set your speed even lower that the physical connection speed.

https://www.juniper.net/documentation/en_US/junos12.3/topics/usage-guidelines/interfaces-configuring-the-interface-bandwidth.html

Hello Matt,

Ahh, I see, so it's cleverer than I thought.

Thank you for your reply.

One more thing, I assume that the "metric" parameter used within an OSPF configuration underneath the interface would be preferred over the bandwith parameter. i.e.

[edit]

interfaces {
          ge-0/0/0 {
                    unit 0 {
                              bandwidth 3m;
                              }
                    }
          }

protocols {
          ospf {
                  area 0 {
                           interface ge-0/0/0 {
                                                metric 100;
                              }
                    }
          }
}

*code is an approximation

Kindest Regards,

Purplezorz