Foundation Summary
The "Foundation Summary" section lists the most important facts from the chapter. Although this section does not list everything that will be on the exam, a well-prepared CCNA candidate should at a minimum know all the details in each Foundation Summary before taking the exam.
Figure 11-21 outlines the basic physical topology and related terminology in a Frame Relay network.
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Figure
11-21 Frame Relay Components
Figure 11-22 depicts a typical partially-meshed Frame Relay network.
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Figure
11-22 Typical Partial-Mesh Frame Relay Network
Table 11-13 outlines the three LMI types, their origin, and the keyword used in the Cisco frame-relay lmi-type interface subcommand.
Table 11-13 Frame Relay LMI Types
|
Name |
Document |
IOS LMI-Type Parameter |
|
Cisco |
Proprietary |
cisco |
|
ANSI |
T1.617 Annex D |
ansi |
|
ITU |
Q.933 Annex A |
q933a |
Figure 11-23 outlines the two Frame Relay encapsulation options on Cisco routers.
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Figure
11-23 Cisco and RFC 1490/2427 Encapsulation
Cisco's Frame Relay implementation defines three different options for assigning subnets and IP addresses on Frame Relay interfaces:
One subnet containing all Frame Relay DTEs
One subnet per VC
A hybrid of the first two options
Cisco IOS software uses some very good choices for default Frame Relay settings:
The LMI type is automatically sensed.
The encapsulation is Cisco instead of IETF.
PVC DLCIs are learned via LMI status messages.
Inverse ARP is enabled (by default) and is triggered when the status message declaring that the VCs are up is received.
Figure 11-24 outlines how Inverse ARP works.
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Figure
11-24 Inverse ARP Process