CCIE Pursuit Blog

April 5, 2008

Internetwork Expert Volume II: Lab 6 – Section 10

IP Services – 2 Points

10.1 CDP

Configure CDP with the following parameters:

1) Send updates every 5 seconds
2) Discard CDP entries after 15 seconds
3) r4 should include it’s lo0 IP address in the CDP packet for identification

This should be easy…except that we’re dealing with the LAN segment that we used L2 tunneling on back in section 1.  But that doesn’t matter because we need to make these changes in global configuration.

cdp timer

Defaults
60 seconds

cdp holdtime

Defaults
180 seconds

cdp source-interface

r4(config)#cdp timer 5
r4(config)#cdp hold 15
r4(config)#cdp source-interface lo0
r4(config)#do sh cdp
Global CDP information:
        Sending CDP packets every 5 seconds
      Sending a holdtime value of 15 seconds
        Sending CDPv2 advertisements is  enabled
        Source interface is Loopback0

Before setting CDP source interface to lo0:
sw2(config)#do sh cdp nei fa0/18 det
————————-
Device ID: r4
Entry address(es):
  IP address: 191.1.48.4
Platform: Cisco 2651XM,  Capabilities: Router Switch IGMP
Interface: FastEthernet0/18,  Port ID (outgoing port): FastEthernet0/1
Holdtime : 11 sec
—output truncated—

After setting CDP source interface to lo0:
sw2(config)#do sh cdp nei fa0/18 det
————————-
Device ID: r4
Entry address(es):
  IP address: 150.1.4.4
Platform: Cisco 2651XM,  Capabilities: Router Switch IGMP
Interface: FastEthernet0/18,  Port ID (outgoing port): FastEthernet0/1
Holdtime : 12 sec
—output truncated—

10.2 UDP Echo

I had no idea on this task:

“Configure sw2 to respond to UPD echoes from a network management station with the IP address 191.1.77.100.”
“sw2 should not respond to packets sent to the UDP ‘discard’ and ‘chargen’ ports from this network management station.”

service udp-small-servers

sw2(config)#access-list 100 deny udp any any eq ?
  discard        Discard (9)

‘chargen’ = ?

Chargen

Chargen is short for Character Generator and is a service that generates random characters either in one UDP packet containing a random number (between 0 and 512) of characters, or a TCP session. The UDP Chargen server looks for a UDP packet on port 19 and responds with the random character packet.

I had to travel to the InterTubes to find this, but IE has a slick trick:

sw2#telnet 150.1.8.8 ?
—output truncated—
  chargen            Character generator (19) <-there’s my UDP port
  cmd                Remote commands (rcmd, 514)
  daytime            Daytime (13)
  discard            Discard (9)
—output truncated—

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