CCNA Cisco Certified Network Associate Study Guide - FTP Server

516 Chapter 10 � Wide Area Networking Protocols
DDR with Access Lists
You can use access lists to be more specific about what is interesting traffic.
In the preceding example we just set the dialer list to allow any IP traffic to
bring up the line. That is great if you are testing, but it can defeat the purpose
of why you use a DDR line in the first place. You can use extended access
lists to set the restriction, for example, to only e-mail or Telnet.
Here is an example of how you define the dialer list to use an access list:
804A(config)#dialer-list 1 list 110
804A(config)#access-list 110 permit tcp any any eq smtp
804A(config)#access-list 110 permit tcp any any eq telnet
804A(config)#int bri0
804A(config-if)#dialer-group 1
In the preceding example, you configure the dialer-list command to
look at an access list. This doesn’t have to be IP; it can be used with any protocol.
Create your list, then apply it to the BRI interface with the dialergroup
command.
Verifying the ISDN Operation
The following commands can be used to verify legacy DDR and ISDN:
Ping and Telnet Are great IP tools for any network. However, your
interesting traffic must dictate that Ping and Telnet are acceptable
as interesting traffic to bring up a link. Once a link is up, you can ping or
telnet to your remote router regardless of your interesting traffic lists.
Show dialer Gives good information about your dialer diagnostic
information and shows the number of times the dialer string has been
reached, the idle-timeout values of each B channel, the length of cal, and
the name of the router to which the interface is connected.
Show isdn active Shows the number called and whether a call is in
progress.
Show isdn status Is a good command to use before trying to dial.
Shows if your SPIDs are valid and if you are connected and communicating
with layers 1 through 3 information to the provider’s switch.