Interface Status

[RakanPastore]

Hi, quick nooby question

Does an interface goes down if the other end of the link is down ? in gns3 it doesnt happen, does anyone knows how it works in real gear.

[Martin L · Accepted solution]

Yes, if interface goes down on one end of a link (cable), the other end of the link is down as well. 

if interface is shutdown on one end of a link (cable), the other end of the link is down as well.

if there is a speed mismatch on a link, interfaces will go down.

GNS3, CML are Virtual emulators that have no physical wires (links), there are no link layer 1 keepalive frames in most of virtual gear (emulators) we use today.  Emulator means it runs on real IOS, virtual IOS, or IOL/IOU.

Simulators, like Packet Tracer, have this working properly because software developers wrote the code to behave close to normal operations.  PT has its limitations but it is good lab to practice CCNA level.  I would recommend having PT as a back up tool.

Regards, ML
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[RakanPastore]

Thank you so much

[Martin L]

One thing I forgot to mentioned is that Serial interfaces in GNS3 do work like in real gear.  Somehow they were able to figure out how to "emulate" layer 1 for serial interfaces but not for Ethernet.
Speed mismatch may bring interface link down if auto-negotiation does not work.
Duplex does not bring interfaces down.