PPP Error Recovery: LAPB

I was asked to configure LAPB for error recovery on a PPP link the other day. I had two questions: 1) What’s LAPB? 2) How? The latter is pretty simple, the former much more complex.

First, in the interest of time, let’s talk about how this is done.

Router(config)#int s0/0/0
Router(config-if)#encapsulation ppp
Router(config-if)#ppp reliable-link

That’s it! Now, what exactly have we accomplished? By enabling LAPB we’ve inserted another layer of error-checking in our link that’s transparent to upper layers. NOTE: LAPB can only be used on unique PPP circuits, not multilinks. If you’re looking for a link quality solution for multilinks, check out LQM.

Layer 2 Protocols on Serial Links

Earlier today I was tasked with getting two serial interfaces to talk with each other. Frame-relay is far from my strong suit, so I question-marked my way through the FR commands, making up DLCIs, adding map statements, etc. After several minutes with no luck I looked at the solution. As it turns out, Frame-relay was entirely unnecessary! And so began my Layer 2 serial interface education.

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