The Many Uses of PPP

Lab 9: Configuring HDLC ”Part II

Lab Walkthrough

Attach the serial cables as shown in Figure 3-2, ensuring that a DTE side is connected to a DCE side. If you forgot which side is which, perform the show controller command to show the cable type (DCE-DTE) attached to this interface. If the routers are connected in a back-to-back manner using serial cables, the clockrate command will be needed on the DCE side of the link. If the routers are connected using CSU/DSUs, the CSU/DSU is the DCE device, and the serial interface and cable to the CSU/DSU are DTE devices. Because configurations with CSU/DSUs are actually a DTE configuration to the router, you do not need to use the clock rate command.

The distribution router, acme_dist, will be the DCE side of the link for both connections. To configure this router, perform the following:

Step 1. (Optional) Configure a hostname of acme_dist.

Step 2. Configure Serial 5 and Serial 1 for HDLC by using the Encapsulation hdlc statement.

Step 3. Configure a clock rate on Serial 1 and Serial 5.

Step 4. Configure STAC compression on Serial 1.

Step 5. Configure an IP address for both serial interfaces.

Step 6. (Optional) Configure a routing protocol.

Example 3-12 demonstrates these steps.

Example 3-12 Configure HDLC DCE Interfaces

 Router# Router#  conf t  Enter configuration commands, one per line.  End with CNTL/Z. Router(config)#  hostname acme_dist  acme_dist(config)#  interface serial 5   acme_dist(config-if)#  encapsulation hdlc    This is optional, HDLC is default    acme_dist(config-if)#  clock rate 56000    Tells the router to send a clock    acme_dist(config-if)#  compress stac    Enables STAC compression   acme_dist(config-if)#  ip address 192.168.128.9 255.255.255.252  acme_dist(config-if)#  no shut  acme_dist(config-if)#  exit  acme_dist(config)# acme_dist(config)#  interface serial 1  acme_dist(config-if)#  clock rate 1000000  acme_dist(config-if)#  ip address 192.168.128.5 255.255.255.252  acme_dist(config-if)#  no shut  acme_dist(config-if)#  exit  acme_dist(config)#  acme_dist(config)#  router eigrp 2001    This is optional, configures    acme_dist(config-router)#  network 192.168.128.0    EIGRP as the routing protocol     for this network   acme_dist(config-router)#  ^Z  acme_dist# 

Moving on to the credit card center, you must also configure this router for HDLC. The router needs compression configured so that it can understand payload compression. To make this lab practical, you also need to add an IP address, a routing protocol, and a host name . Example 3-13 illustrates the configuration of the credit card center, the cc_center router.

Example 3-13 HDLC Configuration on the DTE Side of the Network

 Router#  conf t  Enter configuration commands, one per line.  End with CNTL/Z. Router(config)#  hostname cc_center  cc_center(config)#  interface serial 0  cc_center(config-if)#  encapsulation hdlc  cc_center(config-if)#  compress stac  cc_center(config-if)#  ip address 192.168.128.10 255.255.255.252  cc_center(config-if)#  no shut  cc_center(config-if)#  exit  cc_center(config)# cc_center(config)#  router eigrp 2001  cc_center(config-router)#  network 192.168.128.0  cc_center(config-router)#  ^Z  cc_center# 

Finally, Example 3-14 shows the configuration for the Wisconsin branch. This example takes advantage of the Cisco defaults and the Cisco convention that allows for minimal unique parsing of the command. For example, co can be either configure or copy, but ' cop ' is unique, so cop is sufficient. Example 3-14 demonstrates these time-saving steps.

Example 3-14 HDLC Configuration of wi_branch, Using Defaults and Shortened Keystrokes

 Router#  conf t  Enter configuration commands, one per line.  End with CNTL/Z. Router(config)#  hostname wi_branch  wi_branch(config)#  int s0  wi_branch(config-if)#i  p   add 192.168.128.6 255.255.255.252  wi_branch(config-if)#  no shut  wi_branch(config-if)# wi_branch(config-if)# wi_branch(config-if)#  router eigrp 2001  wi_branch(config-router)#  network 192.168.128.0  wi_branch(config-router)#  ^Z  wi_branch# 

Reviewing the configurations in their entirety, you have the following listings in Example 3-15.

Example 3-15 Configuration Listings for Lab 9, ACME Finance

  Distribution Router (acme_dist)   hostname acme_dist   !   <<<text omitted>>>   !   interface Serial1   ip address 192.168.128.5 255.255.255.252   clockrate 1000000   !   <<<text omitted>>>   !   interface Serial5   ip address 192.168.128.9 255.255.255.252   clockrate 56000   compress stac   !   <<<text omitted>>>   !   router eigrp 2001   network 192.169.128.0  ________________________________________________________________________________  Credit Card Center (cc_center)   hostname cc_center   !   interface Serial0   ip address 192.168.128.10 255.255.255.252   no ip directed-broadcast   no ip mroute-cache   no fair-queue   compress stac   !   <<<text omitted>>>   !   router eigrp 2001   network 192.168.128.0  ________________________________________________________________________________  Wisconsin Branch (wi_branch)   hostname wi_branch   !   <<<text omitted>>>   !   interface Serial0   ip address 192.168.128.6 255.255.255.252   no ip mroute-cache   no fair-queue   !   <<<text omitted>>>   !   router eigrp 2001  network 192.168.128.0 

To verify this particular configuration, a couple of commands are useful: show interface serial x, show ip eigrp neighbors, and, of course, ping. When the lab is fully functional you see two EIGRP neighbors on the acme_dist router, one to each of the other routers. The show interface commands show the line up, the protocol up, and DCD, DSR, DTR, RTS, and CTS all in an up state.