Quick question about DLCI in Frame Relay from ICDN1. The answer is probably obvious to a lot of you, but it's confusing me. The study guide advises:
Quote:
When R1 needs to forward a packet to R2, it encapsulates the Layer 3 packet into a Frame Relay header and trailer and then sends the frame. R1 uses a Frame Relay address called a DLCI in the Frame Relay header, with the DLCI identifying the correct VC to the provider. This allows the switches to deliver the frame to R2, ignoring the details of the Layer 3 packet and looking at only the Frame Relay header and trailer. Recall that on a point-to-point serial link, the service provider forwards the frame over a physical circuit between R1 and R2.
I got the impression that the virtual circuit is a route provided by the service provider to allow the packet to follow a logical path through the service providers network to the destination router. My question is how does the R1 router know what to populate the DLCI with? If i have two networks connected using a frame relay WAN and R1 forwards a packet with the destination of a device on the network connected to R2. I assume the SP can change the logical route and use different VC's. How does the DLCI update on R1 to handle this?
Sorry if I'm being really thick!
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