Your CCNA and CCENT exam achievements is dependent on realizing how to configure and troubleshoot HDLC and PPP on Cisco routers, as very well as figuring out the discrepancies and similarities between the two. Right now we will choose a glance at HDLC and some standard router configurations, and in upcoming CCNA and CCENT certification exam tutorials, we are going to examine PPP in element.
With a place-to-level WAN hyperlink this kind of as the following, we’ve got two alternatives for encapsulation – HDLC and PPP. (HDLC, PPP, and Frame Relay do not operate on LANs – you would not configure them on Ethernet interfaces.)
We’re not likely to focus on HDLC for extensive, considering that you will find not substantially to say about it – but what there is to say is extremely important! The version of HDLC made use of by Cisco routers is the default encapsulation kind on Serial interfaces, verifiable with the display interface serial command. (Only the portion of this command’s output working with the PTP WAN hyperlink will be proven in this part.)
R1#show interface serial 1
Serial1 is up, line protocol is up
Hardware is High definition64570
Net address is 172.12.13.1/24
MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation HDLC, loopback not set
R3#exhibit int serial1
Serial1 is up, line protocol is up
Hardware is Hd64570
Online address is 172.12.13.3/24
MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation HDLC, loopback not established
At this place, just about every associate in the PTP hyperlink can ping the other.
R1#ping 172.12.13.3
Variety escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 172.12.13.3, timeout is 2 seconds:
!!!!!
Good results level is 100 % (5/5), spherical-journey min/avg/max = 36/36/36 ms
R3#ping 172.12.13.1
Style escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 172.12.13.1, timeout is 2 seconds:
!!!!!
Achievement amount is 100 p.c (5/5), round-journey min/avg/max = 32/35/36 ms
This individual version of the Higher Details-Connection Handle encapsulation is Cisco-proprietary, a extravagant way of stating “only Cisco routers fully grasp this encapsulation kind”. If a router at the finish of a PTP connection is operating HDLC encapsulation, the distant companion in the url must do so as properly.
If a single of the routers is operating a different encapsulation sort, the bodily interfaces will even now be up, but the line protocol will go down and IP connectivity will be lost. To illustrate, I’ll adjust the encapsulation style on R3’s Serial1 interface to the Level-To-Position Protocol (PPP).
R3(config-if)#exit
R3(config)#int serial 1
R3(config-if)#encapsulation ppp
A handful of seconds afterwards, 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, modified point out to down
demonstrate interface serial 1 on both equally routers verifies that the actual physical interface is up, but the line protocol is down. IP connectivity is missing.
R3#demonstrate interface serial 1
Serial1 is up, line protocol is down
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:
…..
Achievements fee is percent (/5)
R1#present interface serial 1
Serial1 is up, line protocol is down
R1#ping 172.12.13.3
Variety escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 172.12.13.3, timeout is 2 seconds:
…..
Results price is per cent (/5)
The encapsulation mismatch has brought the line protocol down, and to deliver it back again up, we only need to make the encapsulation types match once more. We are going to do just that in the upcoming installment of my exclusive Cisco CCENT / CCNA certification test tutorial collection!