line protocol

[siskotech]

Line up line protocol up,

In ethernet interface, what is this protocol?

Thanks..

[Richard Burts · Accepted solution]

This protocol was a means of determining whether the interface was in an operational state (outbound data could be transmitted successfully). In earlier versions of Ethernet this protocol used an Ethernet keepalive message to determine the operational state. The keepalive was an Ethernet frame in which the MAC address of the interface was the source MAC (as expected) and was also used as the destination MAC. So in essence it was a frame sent to yourself. As long as the interface detected its keepalive messages the line protocol was up. If keepalives failed (the interface was disconnected from the media, the media was broken, etc) then the line protocol went down. As Ethernet technology has evolved (higher speeds, different media, switch connections, etc) the mechanics of the protocol have evolved but the purpose is still to determine the operational state of the interface.

HTH

Rick

[Richard Burts]

This URL has a discussion of the Ethernet keepalive that you may find helpful

http://www.cisco.com/en/US/tech/tk827/tk369/technologies_tech_note09186a008048cffc.shtml#t3

HTH

Rick

[siskotech]

Is this keep alive (In old type of switches as you described in detail)  going out from the switch, reach other switch and come back?

[Richard Burts]

That type of Ethernet keepalive for designed for environments like the 10base5 and not so much a switched environment. In a switched environment the keepalive has the local MAC address as the destination MAC and since the switch would associate the destination MAC as being on this interface then it would not forward the keepalive to the other switch.

HTH

Rick