T1 PPP and HDLC Configuration

Using T1 Point to Point links between a branch office and a headquarter site is a common architectural deployment. This lab will discuss and demonstrate the configuration of this WAN links using the PPP and HDLC Layer 2 Protocols.

Real World Application & Core Knowledge

As a network engineer you will encounter T1 links very often as T1’s are the de facto standard of nearly all small branch offices. T1’s operate at 1.544Mbps (1544Kbps) and now days commonly drop into a facilities point of presence (pop) or commonly (BPOP) as the POP is most commonly in the basement.

T1’s can also be fractional T1’s where the bandwidth is limited to 512Kbps, 768Kbps, or even 1Mbps. Commonly with fractional T1’s you’ll have the ability to “burst” which gives the router the ability to send more then its committed information rate (CIR) at specific times of the clocking rate. However, those concepts are beyond the scope of the CCNA blueprint.

Most Newer T1’s installations are copper twisted pair T1 which connects to a WIC-1DSU-T1, WIC-1DSU-T1-V2 or other integrated CSU/DSU T1 controllers. However you may encounter older T1 installations where the CSU/DSU is external and you’ll see a v.35 cable ran to a WIC-1T or WIC-2T.

WIC-1T’s are the most common lab serial interfaces and when configuring such interfaces you’ll be required to set the clock rate on the DCE (Data Communications Equipment) which is done by the ISP whereas the DTE (Data Termination Equipment) is done at the consumer end.

In this lab you’ll familiarize yourself with the following commands;

Command	Description
show controller serial #/#	Shows controller information about the specified serial interface including the clock rate and cable termination type (DTE or DCE)
clock rate #	This command is executed in serial interface configuration mode to set the clock rate of a DCE termination point of a serial link.
encapsulation [ HDLC \| PPP ]	This command when executed in Serial interface configuration mode configures the interface encapsulation to Cisco HDLC (High-Level Data Link Control protocol) or the Industry Standard PPP (Point to Point Protocol)
show interface serial #/#	This command when executed in privileged mode will display Serial interface information such as encapsulaton, MTU, up time, current utilization and more.

Lab Prerequisites

If you are using GNS3 than load the Free CCNA Workbook GNS3 topology than start devices; R1 and R2.
Establish a console session with devices R1 and R2 than configure the devices respected hostname(s).
Configure R1’s Serial0/1 interface with the IP address 172.18.21.1/30 and R2’s Serial0/1 interface with the IP address 172.18.21.2/30

Lab Objectives

Configure both R1 and R2’s Serial0/1 interface to encapsulate traffic using the HDLC encapsulation.Verify your configuration by using a show command to display the interface encapsulation and by pinging R2 from R1.
Configure both R1 and R2’s Serial0/1 interface to encapsulate traffic using the PPP encapsulation. Verify your configuration by using a show command to display the interface encapsulation and by pinging R2 from R1.

Lab Instruction

Objective 1. – Configure both R1 and R2’s Serial0/1 interface to encapsulate traffic using the HDLC encapsulation. Verify your configuration by using a show command to display the interface encapsulation and by pinging R2 from R1.

The configuration part of this objective is a trick question however the commands shown below will demonstrate how to configure HDLC. Keep in mind that HDLC is the default serial interface encapsulation on Cisco routers. You can verify the serial interface encapsulation by using the show interface serial #/# command in privileged mode.

R1 con0 is now available



Press RETURN to get started.



R1>enable
R1#configure terminal
Enter configuration commands, one per line.  End with CNTL/Z.
R1(config)#interface Serial0/1
R1(config-if)#encapsulation hdlc
R1(config-if)#no shutdown
R1(config-if)#end
R1#
%SYS-5-CONFIG_I: Configured from console by console
R1#
%LINK-3-UPDOWN: Interface Serial0/1, changed state to up
R1#
%LINEPROTO-5-UPDOWN: Line protocol on Interface Serial0/1,
changed state to up
R1#

R2 con0 is now available



Press RETURN to get started.



R2>enable
R2#configure terminal
Enter configuration commands, one per line.  End with CNTL/Z.
R2(config)#interface Serial0/1
R2(config-if)#encapsulation hdlc
R2(config-if)#no shutdown
R2(config-if)#end
R2#
%SYS-5-CONFIG_I: Configured from console by console
R2#
%LINK-3-UPDOWN: Interface Serial0/1, changed state to up
R2#
%LINEPROTO-5-UPDOWN: Line protocol on Interface Serial0/1,
changed state to up
R2#

Interface Encapsulation verification shown below;

R1#show interface Serial0/1
Serial0/1 is up, line protocol is down 
  Hardware is M4T
  MTU 1500 bytes, BW 1544 Kbit/sec, DLY 20000 usec, 
     reliability 255/255, txload 1/255, rxload 1/255
  Encapsulation HDLC, crc 16, loopback not set
  Keepalive set (10 sec)
  Restart-Delay is 0 secs
  Last input never, output 00:00:07, output hang never
  Last clearing of "show interface" counters never
  Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0
  Queueing strategy: weighted fair
  Output queue: 0/1000/64/0 (size/max total/threshold/drops) 
     Conversations  0/1/256 (active/max active/max total)
     Reserved Conversations 0/0 (allocated/max allocated)
     Available Bandwidth 1158 kilobits/sec
  5 minute input rate 0 bits/sec, 0 packets/sec
  5 minute output rate 0 bits/sec, 0 packets/sec
     0 packets input, 0 bytes, 0 no buffer
     Received 0 broadcasts, 0 runts, 0 giants, 0 throttles
     0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort
     38 packets output, 2332 bytes, 0 underruns
     0 output errors, 0 collisions, 4 interface resets
     0 unknown protocol drops
     0 output buffer failures, 0 output buffers swapped out
     5 carrier transitions     DCD=up  DSR=up  DTR=up  RTS=up  CTS=up

R1#

Ping verification from R1 to R2 shown below;

R1#ping 172.18.21.2

Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 172.18.21.2, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 24/42/88 ms
R1#

Objective 2. – Configure both R1 and R2’s Serial0/1 interface to encapsulate traffic using the PPP encapsulation. Verify your configuration by using a show command to display the interface encapsulation and by pinging R2 from R1.

R1#configure terminal
Enter configuration commands, one per line.  End with CNTL/Z.
R1(config)#interface Serial0/1
R1(config-if)#encapsulation ppp
R1(config-if)#end
R1#
%SYS-5-CONFIG_I: Configured from console by console
R1#
%LINEPROTO-5-UPDOWN: Line protocol on Interface Serial0/1, changed
state to down
R1#

R2#
%LINEPROTO-5-UPDOWN: Line protocol on Interface Serial0/1, changed
state to down
R2#configure terminal
Enter configuration commands, one per line.  End with CNTL/Z.
R2(config)#interface Serial0/1
R2(config-if)#encapsulation ppp
R2(config-if)#end
R2#
%SYS-5-CONFIG_I: Configured from console by console
%LINEPROTO-5-UPDOWN: Line protocol on Interface Serial0/1, changed
state to up
R2#

You’ll notice when changing the encapsulation from HDLC to PPP on R1 that the line protocol will go down, this is due to an encapsulation mis-match. Once R2’s Serial0/1 interface is configured with the matching encapsulation the line protocol will go back up.

Encapsulation and ping verification shown below;

R1#
%LINEPROTO-5-UPDOWN: Line protocol on Interface Serial0/1, changed
state to up
R1#
R1#show interface Serial0/1
Serial0/1 is up, line protocol is up 
  Hardware is M4T
  Internet address is 172.18.21.1/30
  MTU 1500 bytes, BW 1544 Kbit/sec, DLY 20000 usec, 
     reliability 255/255, txload 1/255, rxload 1/255
  Encapsulation PPP, LCP Open
  Open: IPCP, CDPCP, crc 16, loopback not set
  Keepalive set (10 sec)
  Restart-Delay is 0 secs
  Last input 00:00:40, output 00:00:07, output hang never
  Last clearing of "show interface" counters 00:04:34
  Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0
  Queueing strategy: weighted fair
  Output queue: 0/1000/64/0 (size/max total/threshold/drops) 
     Conversations  0/1/256 (active/max active/max total)
     Reserved Conversations 0/0 (allocated/max allocated)
     Available Bandwidth 1158 kilobits/sec
  5 minute input rate 0 bits/sec, 0 packets/sec
  5 minute output rate 0 bits/sec, 0 packets/sec
     54 packets input, 2146 bytes, 0 no buffer
     Received 0 broadcasts, 0 runts, 0 giants, 0 throttles
     0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort
     69 packets output, 2553 bytes, 0 underruns
     0 output errors, 0 collisions, 2 interface resets
     12 unknown protocol drops
     0 output buffer failures, 0 output buffers swapped out
     2 carrier transitions     DCD=up  DSR=up  DTR=up  RTS=up  CTS=up

R1#ping 172.18.21.2

Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 172.18.21.2, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 16/49/88 ms
R1#

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