Answers to the Chapter 8 "Do I Know This Already?" Quiz 767
7
What show command will tell you the time that a PVC became active? How does the
router know what time the PVC became active?
The show frame-relay pvc command lists the time since the PVC came up, so you can
subtract this time from the current time of day to derive the time at which the VC came
up. The router learns this from an LMI message.
8
What debug options will show Inverse ARP messages?
debug frame-relay events, as shown in Example 8-19 on page 561.
9
What does the acronym LAPD stand for? Is it used as the Layer 2 protocol on dialed ISDN
bearer channels? If not, what is used?
Link Access Procedure, D-channel. LAPD is not used on bearer channels, but instead on
the signaling channel. PPP is typically used on bearer channels.
10
Define the term reference point. List two examples of reference points.
A reference point is an interface between function groups. R, S, T, and U are the reference
points. S and T are combined in many cases and then called the S/T reference point.
Reference points refer to cabling, which implies the number of wires used. In particular,
the S and T points use a four-wire interface; the U interface uses a two-wire cable.
11
Describe the decision process performed by the IOS to attempt to dial a connection using
legacy DDR.
First, some traffic must be routed out the interface to be dialed; this is typically
accomplished by adding static routes pointing out the interface. Then, "interesting" must
be defined; any packets routed out the interface that are considered interesting will cause
the interface to be dialed.
12
If packets from 10.1.1.0/24 were "interesting" in relation to DDR configuration such that
packets from 10.1.1.0/24 would cause a DDR connection out an interface BRI0, list the
configuration commands that would make the IOS think that those packets were
interesting on BRI0.
The access list that follows defines the packets from 10.1.1.0/24. The dialer-list defines
the use of access-list 1 for deciding what is interesting. The dialer-group command
enables that logic on interface BRI0.
access-list 1 permit 10.1.1.0 0.0.0.255
!
dialer-list 2 protocol ip list 1
!
interface bri 0
dialer-group 2
apA.fm Page 767 Monday, March 20, 2000 5:24 PM