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126 Chapter 3: OSI Reference Model & Layered Communication
Answers to Task 3 for Scenario 3-1
Based on the network design illustrated in Figure 3-22, Task 3 for Scenario 3-1 states that
D'Artagnan sends a packet to Porthos (source group-1.local-M, destination group-6.local-M).
D'Artagnan sends this packet inside an Ethernet frame to Router A. The following are the
solutions to exercises 1 through 4 for Task 3.
1
The routing tables are as follows:
In Router A:
In Router D:
2
Router A discards the Ethernet header and adds a Frame Relay header. Router D discards
the Frame Relay header and adds an Ethernet header.
3
Router A places the Frame Relay DLCI for the VC connecting it to Router D into the
address field in the header. Router D places Porthos's Ethernet MAC address into the
destination address field.
4
This is all noise if Porthos cannot get a packet back to D'Artagnan. The following routing
tables show the routes needed for both directions; the routes with asterisks signify routes
required for the routes back to D'Artagnan.
In Router A:
Group
Outgoing Interface
Next Router
group-5
serial 1
--
group-6
serial 1
group-5.local-D
Group
Outgoing Interface
Next Router
group-6
Ethernet 0
--
Group
Outgoing Interface
Next Router
group-1*
Ethernet 0
--
group-5
serial 1
--
group-6
serial 1
group-5.local-D
ch03.fm Page 126 Monday, March 20, 2000 4:58 PM