Your CCNA and CCENT test success depends on realizing how to configure and troubleshoot HDLC and PPP on Cisco routers, as properly as figuring out the variances and similarities concerning the two. Today we will consider a glimpse at HDLC and some fundamental router configurations, and in potential CCNA and CCENT certification exam tutorials, we are going to take a look at PPP in depth.

With a issue-to-position WAN connection these types of as the adhering to, we’ve received two selections for encapsulation – HDLC and PPP. (HDLC, PPP, and Body Relay do not run on LANs – you wouldn’t configure them on Ethernet interfaces.)

We’re not going to talk about HDLC for lengthy, since there’s not a lot to say about it – but what there is to say is extremely essential! The version of HDLC made use of by Cisco routers is the default encapsulation variety on Serial interfaces, verifiable with the display interface serial command. (Only the portion of this command’s output dealing with the PTP WAN backlink will be proven in this segment.)

R1#display interface serial 1

Serial1 is up, line protocol is up

Components is High definition64570

World-wide-web address is 172.12.13.1/24

MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec,

dependability 255/255, txload 1/255, rxload 1/255

Encapsulation HDLC, loopback not set

R3#demonstrate int serial1

Serial1 is up, line protocol is up

Hardware is Hd64570

Web address is 172.12.13.3/24

MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec,

trustworthiness 255/255, txload 1/255, rxload 1/255

Encapsulation HDLC, loopback not set

At this place, each spouse in the PTP connection can ping the other.

R1#ping 172.12.13.3

Type escape sequence to abort.

Sending 5, 100-byte ICMP Echos to 172.12.13.3, timeout is 2 seconds:

!!!!!

Accomplishment level is 100 % (5/5), round-trip min/avg/max = 36/36/36 ms

R3#ping 172.12.13.1

Sort escape sequence to abort.

Sending 5, 100-byte ICMP Echos to 172.12.13.1, timeout is 2 seconds:

!!!!!

Good results rate is 100 percent (5/5), round-trip min/avg/max = 32/35/36 ms

This individual model of the High Knowledge-Backlink Management encapsulation is Cisco-proprietary, a fancy way of declaring “only Cisco routers understand this encapsulation kind”. If a router at the stop of a PTP url is jogging HDLC encapsulation, the distant partner in the connection must do so as perfectly.

If 1 of the routers is functioning yet another encapsulation sort, the bodily interfaces will nevertheless be up, but the line protocol will go down and IP connectivity will be misplaced. To illustrate, I am going to improve the encapsulation variety on R3’s Serial1 interface to the Issue-To-Point Protocol (PPP).

R3(config-if)#exit

R3(config)#int serial 1

R3(config-if)#encapsulation ppp

A few seconds later on, the line protocol goes down on R3.

2d04h: %SYS-5-CONFIG_I: Configured from console by console

2d04h: %LINEPROTO-5-UPDOWN: Line protocol on Interface Serial1, transformed point out to down

present interface serial 1 on each routers verifies that the actual physical interface is up, but the line protocol is down. IP connectivity is misplaced.

R3#display interface serial 1

Serial1 is up, line protocol is down

R3#ping 172.12.13.1

Type escape sequence to abort.

Sending 5, 100-byte ICMP Echos to 172.12.13.1, timeout is 2 seconds:

…..

Good results level is % (/5)

R1#demonstrate interface serial 1

Serial1 is up, line protocol is down

R1#ping 172.12.13.3

Form escape sequence to abort.

Sending 5, 100-byte ICMP Echos to 172.12.13.3, timeout is 2 seconds:

…..

Good results rate is percent (/5)

The encapsulation mismatch has brought the line protocol down, and to deliver it again up, we just have to have to make the encapsulation kinds match yet again. We’ll do just that in the subsequent installment of my exceptional Cisco CCENT / CCNA certification test tutorial sequence!