1.3 “n-isl”means “forced to become ISL”?

Judging from the explanation, “negotiated”sounds overwhelming to me.



  • Negotiated simply means that DTP was used between switches to form the trunk, and to agree on the protocol to use (dot-1q or isl).

    Recent switches no longer use isl - standardized on dot-1q.

    Judging from the explanation, “negotiated”sounds overwhelming to me.

  • peetypeety ✭✭✭

    Lemme tell you a bedtime story about Ethernet autonegotiation that's probably somewhat similar to this "negotiation".  Cisco thinks that if you set speed/duplex, it should therefore treat the port as manually configured, and not participate in any sort of auto-negotiation. As such, the other end of the link can sense link speed (FE has FLP, E doesn't, etc.), but it can't sense duplex (there are no signal pulses to reflect the duplex _setting_ aside from autonegotiation).  As a result, Cisco's stance is that a link with manual settings on one end should have manual settings on the other end.

    However, some other vendors are much smarter about this whole process.  If you manually set a port to a particular speed and/or duplex value, those vendors still participate in autonegotiation, BUT they only offer the speed/duplex setting that's configured.  In other words, it wants to autonegotiate a perfect match.

    What you're seeing with n-isl and the other side set to isl is that kind of negotiation: one side says I'm willing to trunk if you're willing to do it via ISL.  I'd consider that a whole lot better than just setting (possibly mismatched) encapsulations on opposite ends and disabling DTP altogether, causing packet loss.


    Thanks, guys.

    Appreciate your help.


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