Thursday, March 09, 2006


Configuring data compression on PPP link. (Question #33)

Consider two routers connected back-to-back via serial links with PPP encapsulation. The links are already up. You decide to configure STAC data compression on the link and so you enter configuration mode on the routers at either end and type in compress stac under the interface configuration.

However, when you then issue a show compress command you see that compression is not enabled. Here is the output from one router

R1#sh runn int s 2
Building configuration...

Current configuration : 112 bytes
interface Serial2
ip address
encapsulation ppp
no keepalive
compress stac

R1# show compress
Compression not active
uncompressed bytes xmt/rcv 0/0
compressed bytes xmt/rcv 0/0
1 min avg ratio xmt/rcv 0.000/0.000
5 min avg ratio xmt/rcv 0.000/0.000
10 min avg ratio xmt/rcv 0.000/0.000
no bufs xmt 0 no bufs rcv 0
resyncs 0

What is the problem here? Why isn't compression getting enabled?


IS-IS DIS identification. (Question #32)

Given the following output from a show isis database command on a Cisco router, can you identify
  1. the Designated Intermediate Systems (DIS) in the network
  2. the hostname of the router where this command was issued

IS-IS Level-1 Link State Database:
LSPID LSP Seq Num LSP Checksum LSP Holdtime ATT/P/OL
R2.00-00 * 0x0000008E 0xE8BB 819 1/0/0
R3.00-00 0x0000007C 0x710E 704 0/0/0
R4.00-00 0x00000079 0x3FD3 691 0/0/0
R5.00-00 0x00000076 0x0D99 879 0/0/0
R5.01-00 0x00000080 0xA481 644 0/0/0
IS-IS Level-2 Link State Database:
LSPID LSP Seq Num LSP Checksum LSP Holdtime ATT/P/OL
R1.00-00 0x00000080 0x4DED 971 0/0/0
R2.00-00 * 0x0000007F 0xBCA2 732 0/0/0
R6.00-00 0x0000005A 0xFE20 838 0/0/0
R6.01-00 0x00000057 0xA2B2 717 0/0/0
R8.00-00 0x0000005A 0x6AE7 1048 0/0/0

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