Snapshot DDR
In all the previous dial-up examples, we used static routes to define the routing tables for dial-up connections. On small networks, static routes are easily managed, but on larger networks they can quickly get out of hand. However, running a routing protocol in the presence of DDR is a problem because normal routing protocols would keep DDR links up forever with their constant route updates. In some situations this might be acceptable, but it begs the question of why you're using DDR in the first place.
Snapshot routing was designed to allow the use of routing protocols across DDR connections without keeping the line active constantly. As the name implies, snapshot routing means that the routing protocols are allowed to take a "snapshot" of the network's state at specified intervals rather than sending and receiving constant updates. Therefore, dial-up links come up only at a configurable interval, which saves the headache of static route management and keeps the dial-up link's usage to a minimum. Snapshot routing is compatible with RIP (IP and IPX), EIGRP, IGRP, RTMP (AppleTalk), and RTP (Vines), all of which are distance-vector protocols.
Configuring a link for snapshot routing requires one end to be a snapshot server and the other end to be a snapshot client. In this example, Office 1 has the local network 10.10.0.0 and serves as the snapshot server; Office 2 has the local network 10.11.0.0 and is the snapshot client. There are two dialer maps at each site: one for the normal traffic (map this address to this phone number) and another for the snapshot routing protocol.
Here's the configuration for Office 1:
hostname office1 ! interface ethernet0 ip address 10.10.1.1 255.255.0.0 ! ! Set the ISDN switch type isdn switch-type basic-ni1 ! interface BRI0 ! Don't need an IP address because we are using the dialer interface no ip address encapsulation ppp dialer rotary-group 0 ! Our local SPIDs for our ISDN lines isdn spid1 014105551212111 5551212 isdn spid2 014105551213111 5551213 ! ! Configure the dialer interface interface dialer 0 ip unnumbered ethernet0 encapsulation ppp dialer in-band dialer idle-timeout 300 dialer map snapshot 1 name office2 speed 56 ! Map the IPs to the phone numbers at office2 ! There are two maps, one for each ISDN channel ! Broadcast is required here because we are doing routing dialer map ip 10.11.1.1 name office2 speed 56 broadcast 14105551312 dialer map ip 10.11.1.1 name office2 speed 56 broadcast 14105551313 dialer-group 1 ! Enable snapshot server, updates every 30 minutes snapshot-server 30 ! Disable CDP for this interface no cdp enable ! PPP CHAP authentication ppp authentication chap ! Enable multilink for the PPP (2 channels) ppp multilink ! username office1 password letmein ! dialer-list 1 protocol ip permit ! ! Enable RIP router rip network 10.0.0.0 version 2 no validate-update source
Here's the configuration for Office 2:
hostname office2 ! interface ethernet0 ip address 10.11.1.1 255.255.0.0 ! ! Set the ISDN switch type isdn switch-type basic-ni1 ! interface BRI0 ! Don't need an IP address because we are using the dialer interface no ip address encapsulation ppp dialer rotary-group 0 ! Our local SPIDs for our ISDN lines isdn spid1 014105551312111 5551312 isdn spid2 014105551313111 5551313 ! ! Configure the dialer interface interface dialer 0 ip unnumbered ethernet0 encapsulation ppp dialer in-band dialer idle-timeout 300 dialer map snapshot 1 name office1 speed 56 ! Map the IPs to the phone numbers at office1 ! Broadcast is required here because we are doing routing dialer map ip 10.10.1.1 name office1 speed 56 broadcast 14105551212 dialer map ip 10.10.1.1 name office1 speed 56 broadcast 14105551213 dialer-group 1 ! Enable snapshot client, updates every 30 minutes snapshot client 30 600 suppress-statechange-update dialer ! Disable CDP for this interface no cdp enable ! PPP CHAP authentication ppp authentication chap ! Enable multilink for the PPP (2 channels) ppp multilink ! username office2 password letmein ! dialer-list 1 protocol ip permit ! ! Enable RIP router rip network 10.0.0.0 version 2
In this configuration, Office 2 is the snapshot client. Office 2 can exchange routing information whenever the BRI interfaces come up. If the snapshot timeout expires (the timeout is set to 30 minutes), the router is allowed to bring the BRI interface up to exchange routing information even if there is no "interesting" traffic.
12.5.1. Useful show Commands
Here are some show commands that are useful for monitoring DDR on your router.
12.5.1.1. show dialer
This command can be very verbose. It provides detailed information about all your DDR interfaces; to limit the output, you can specify the name of a particular dialer interface.
Router1#show dialer Dialer0 - dialer type = DIALER PROFILE Idle timer (120 secs), Fast idle timer (20 secs) Wait for carrier (30 secs), Re-enable (15 secs) Dialer state is data link layer up Dial String Successes Failures Last called Last status 5552323 0 1 00:00:33 failed BRI0 - dialer type = ISDN Dial String Successes Failures Last called Last status 0 incoming call(s) have been screened. 0 incoming call(s) rejected for callback. BRI0:1 - dialer type = ISDN Idle timer (180 secs), Fast idle timer (20 secs) Wait for carrier (30 secs), Re-enable (15 secs) Dialer state is data link layer up Dial reason: ip (s=192.168.1.1, d=10.1.1.2) Interface bound to profile Dialer0 Time until disconnect 148 secs Current call connected 00:00:33 Connected to 5552323 (Router2) BRI0:2 - dialer type = ISDN Idle timer (120 secs), Fast idle timer (20 secs) Wait for carrier (30 secs), Re-enable (15 secs) Dialer state is idle
The output shows that this router has a Dialer0 interface and a BRI0 interface. Table 12-2 describes a few of the more confusing fields in this output.
|
Field |
Meaning |
|---|---|
|
Timers (Idle/Fast idle/Wait/Re-enable) |
The time, in seconds, for each of the timers. If you don't set any timers in the configuration, these fields reflect the default values. |
|
Dial string |
The dial string (essentially, the phone number) of any logged calls. |
|
Successes/Failures/Last called/Last status |
The number of successful calls; the number of failed calls; the time of the last call; the status of the last call. |
|
Screened/Rejected |
The number of incoming calls that have been screened, and the number of calls that have been rejected by the screening process. A dialer profile can be set up to screen incoming calls and handle them in different ways. The most typical way to handle a screened call is to use caller ID callback. If the callback fails, the call is rejected. |
|
Dialer state |
data link layer up means that the call connected properly. Any other message means there is a problem with the call. |
|
Dial reason |
The source (S) and destination (D) IP addresses for the packet that caused the link to come up. |
12.5.1.2. show dialer map
This command lists all the dialer maps that are defined:
Router1#show dialer map Static dialer map ip 10.1.1.1 name office2 on Dialer1 Static dialer map ip 10.1.1.2 name office3 on Dialer1
12.5.1.3. show isdn active
This command is limited to ISDN interfaces. It provides some valuable information about active ISDN calls:
Router1#show isdn active ---------------------------------------------------------------------------- ISDN ACTIVE CALLS ---------------------------------------------------------------------------- History table has a maximum of 100 entries. History table data is retained for a maximum of 15 Minutes. ---------------------------------------------------------------------------- Call Calling or Called Remote Seconds Seconds Seconds Recorded Charges Type Phone number Node Name Used Left Idle Units/Currency ---------------------------------------------------------------------------- Out 5552323 Router2 88 105 5 0 ----------------------------------------------------------------------------
12.5.1.4. show snapshot
This command displays information about snapshot routing:
Router#show snapshot bri0 Bri0 is up, line protocol is up, snapshot up Options: dialer support Length of each activation period: 3 minutes Period between activations: 30 minutes Retry period on connect failure: 5 For dialer address 0 Current queue: active, remaining active time: 1 minutes Updates received this cycle: ip For dialer address 1 Current queue: client quiet, time until next activation: 27 minutes
Everything in this output should be straightforward except for the dialer address. The dialer address number refers to the rotary group number. Therefore, in this example, we're seeing snapshot information for rotary groups 0 and 1.