IP Pool Design


The purpose of the IP pool is to create and assign a group of addresses, so that when the remote user calls, after the user is authenticated, an IP address is provided from a predefined set of IP addresses. The IP pool assignment in the core router is relatively simple to configure, as shown in Example 10-6.

Example 10-6. Configuration Setting for an IP Pool
 <output omitted> interface Dialer1 description HOME_ISDN_USERS ip unnumbered Loopback0 encapsulation ppp no ip mroute-cache no keepalive dialer in-band dialer idle-timeout 3600 dialer-group 8  peer default ip address pool HOME_ISDN_USERS  fair-queue ppp authentication chap callin ppp multilink !  ip local pool HOME_ISDN_USERS 20.18.15.1 20.18.15.62  <output omitted> 

Under the dialer 1 interface, the definition for the IP address pool is specified. The definition is related to the last statement in the example, which defines the IP pool from 20.18.15.1 to 20.18.15.62 with 62 addresses, or a /26 subnet. The bold statements must match, and it is important not to oversubscribe. Because ISDN is still a dial-in service, expect both peak and non-used hours. It is common practice to use a 10:1 ratio of users to channels. In some cases when it makes business sense, it is better to use a lower ratio to increase the availability of the circuits.

NOTE

In the Cisco ISDN environment for home users, a ratio of 5:1 up to 7:1 works well and does not cause any disconnects or busy signals during peak hours.


To check the status of the pool, use the show ip local pool command, as shown in Example 10-7.

Example 10-7. Checking IP Pool Status
 4500-isdn#  show ip local pool  Pool               Begin          End              Free     In use HOME_ISDN_USERS    20.18.15.1     20.18.15.62      59       3 4500-isdn# 

To check on who the three users are who are currently connected, use the show users all command, as shown in Example 10-8.

Example 10-8. Determining the Users of the IP Pool
 4500-isdn#  show users all  <output omitted> Interface   User           Mode                     Idle          Peer Address Vi13        804-isdn-56    Virtual PPP (Bundle)     00:00:45      10.70.219.20 Vi17        804-isdn-1     Virtual PPP (Bundle)     00:00:00      10.99.251.217 Vi19        776-isdn-3     Virtual PPP (Bundle)     00:02:44      10.121.5.185" <output omitted> 

The command shows information about all users, including the information about incative ports.

Another option here is to show detailed information about every multilink bundle with the show ppp multilink command, as shown in Example 10-9.

Example 10-9. Collecting Multilink Bundle Information
 4500-isdn#  show ppp multilink  <output omitted> Virtual-Access17, bundle name is 804-isdn-1   Bundle up for 00:01:46   Dialer interface is Dialer1   0 lost fragments, 0 reordered, 0 unassigned   0 discarded, 0 lost received, 1/255 load   0x0 received sequence, 0x0 sent sequence   Member links: 1 (max not set, min not set)     Serial0:21, since 00:01:46 Virtual-Access19, bundle name is 776-isdn-3   Bundle up for 12:58:58   Dialer interface is Dialer1   0 lost fragments, 16 reordered, 0 unassigned   0 discarded, 0 lost received, 1/255 load   0x1AA3 received sequence, 0x5392 sent sequence   Member links: 2 (max not set, min not set)     Serial0:7, since 12:58:58     Serial0:22, since 00:00:31 Virtual-Access13, bundle name is 804-isdn-56   Bundle up for 1d11h   Dialer interface is Dialer1   0 lost fragments, 864 reordered, 0 unassigned   0 discarded, 0 lost received, 1/255 load   0x300C received sequence, 0x6463 sent sequence   Member links: 1 (max not set, min not set)     Serial0:12, since 1d11h <output omitted> 

To check which addresses are taken from the pool, use the show ip route command, as shown in Example 10-10.

Example 10-10. Determining Addresses Taken from an IP Pool
 4500-isdn#  show ip route  <output omitted> C       20.18.15.3/32 is directly connected, Dialer1  ! This IP is taken  D       10.18.15.0/26 is a summary, 00:09:45, Null0 C       20.18.15.51/32 is directly connected, Dialer1  ! This IP is taken  C       20.18.15.37/32 is directly connected, Dialer1  ! This IP is taken  C       20.18.254.131/32 is directly connected, Loopback0 D       20.85.130.72/32 [90/409600] via 161.68.99.1, 00:09:45, Ethernet0 S*   0.0.0.0/0 [1/0] via 161.68.99.1 4500-isdn# 

A better option here is to use the show ip local pool name command, as shown in Example 10-11.

Example 10-11. Determining Addresses Within an IP Pool
 4500-isdn#  show ip local pool HOME_ISDN_USERS  Pool             Begin           End             Free    In use   Cache Size  HOME_ISDN_USERS  20.18.15.1     20.18.15.62       59       3          20 Available addresses:    20.18.15.3         Vi13                        804-isdn-56    20.18.15.51        Vi19                        776-isdn-3    20.18.15.37        Vi17                        804-isdn-1 <output omitted> 

This command displays the available addresses in the pool. Also, the command shows the IP addresses that are currently in use and the virtual interface that is assigned to the user of that IP address.




Troubleshooting Remote Access Networks CCIE Professional Development
Troubleshooting Remote Access Networks (CCIE Professional Development)
ISBN: 1587050765
EAN: 2147483647
Year: 2002
Pages: 235

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