Help configuring back-to-back serial ports

Attachment not found.

Hi everyone,

I’m building my lab for the CCNA. (see attached). I have (3) X 2501 routers and I’m having problems with the back-to-back serial ports connections. I purchased two (2) DCE-DTE male-to-male crossover DB60 cables for this purpose. I configured the serial ports according with standard procedures i.e. setting up clocking on the DCE interface. However, I’m not getting connectivity and I get a “line protocol down” on both interfaces. I configured PPP encapsulation on both interfaces but still same result. I’m probably overlooking something, but I can’t find what the problem is.

The following is the output for: show run, show controllers and show int on both routers.

Any help would be greatly appreciated. Thanks,

OUTPUT IN R1:

LAB-R1#sh run
version 11.3
service timestamps debug uptime
service timestamps log uptime
no service password-encryption
!
hostname LAB-R1
!
no ip domain-lookup
!
!
interface Ethernet0
description CONNECTION TO LAB-S1
ip address 192.168.1.20 255.255.255.0
!
interface Serial0
description CONNECTION TO LAB-R2
ip address 192.168.2.1 255.255.255.0
encapsulation ppp
no ip mroute-cache
clockrate 1000000

OUTPUT CUT

CONTROLLERS:

LAB-R1#sh controllers s 0
HD unit 0, idb = 0xA1C6C, driver structure at 0xA6F08
buffer size 1524 HD unit 0, V.35 DCE cable, clockrate 1000000
cpb = 0xE1, eda = 0x4940, cda = 0x4800

OUTPUT CUT

LAB-R1#sh int s0
Serial0 is up, line protocol is down
Hardware is HD64570
Description: CONNECTION TO LAB-R2
Internet address is 192.168.2.1/24
MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec, rely 255/255, load 1/255
Encapsulation PPP, loopback not set, keepalive set (10 sec)
LCP ACKsent

OUTPUT IN R2:

LAB-R2#sh run
version 12.3
service timestamps debug datetime msec
service timestamps log datetime msec
no service password-encryption
!
hostname LAB-R2
!
boot-start-marker
boot-end-marker
!
!
no aaa new-model
ip subnet-zero
no ip domain lookup
!
!
interface Ethernet0
description Connection to T.F.T.P. server
ip address 192.168.3.1 255.255.255.0
shutdown
!
interface Serial0
description Connection to LAB-R1
ip address 192.168.2.20 255.255.255.0
encapsulation ppp
!
interface Serial1
description Connection to "LAB-R3" (DCE)
ip address 192.168.4.1 255.255.255.0
shutdown
!
ip http server
ip classless

LAB-R2#sh controllers s 0
LAB-R2#sh controllers s 0
HD unit 0, idb = 0x1EFBE4, driver structure at 0x1F0FC8
buffer size 1524 HD unit 0, V.35 DTE cable
cpb = 0xE1, eda = 0x5140, cda = 0x5000
RX ring with 16 entries at 0xE15000

LAB-R2#sh int s0
Serial0 is up, line protocol is down
Hardware is HD64570
Description: Connection to LAB-R1
Internet address is 192.168.2.20/24
MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation PPP, LCP Listen, loopback not set
Keepalive set (10 sec)\

CCNA LAB.jpg

Find more posts tagged with

Save $250 on 2025 certification boot camps from Infosec!

Book now with code EOY2025

Button

Comments

mikej412

Just a quick glance, since I'm about to run out the door.....

It looks like your serial ports are on all different networks.... nevermind. 192.168.2.0 on Serial 0 on both R1 & R2.

What are your IOS Versions & Feature set (one of your configs says 11.3 which is old).

How much memory do you have on the routers?

(show version show give that information)

You cut off the show interface information right at the PPP information....
you can run debug ppp to see if you can tell if and why PPP negotiation is failing..... or you can just try the default HDLC encapsulation.

Other than that -- it's a good "first attempt" and you did a good job providing most of the relevant troubleshooting information.....

hodgey87

This is usually a logical issue ie different encapsulation types PPP HDLC or missing clockrates etc see if HDLC works

----Edit----
Beat me to it mike

Islander954

When I configured them the first time I left the default encapsulation (HDLC). It didn't work. That's why I tried PPP

Islander954

Thanks, here is the output from "show version"

R1:

LAB-R1#sh ver
Cisco Internetwork Operating System Software
IOS (tm) 2500 Software (C2500-I-L), Version 11.3(6), RELEASE SOFTWARE (fc1)
Copyright (c) 1986-1998 by cisco Systems, Inc.
Compiled Tue 06-Oct-98 21:37 by kpma
Image text-base: 0x03029490, data-base: 0x00001000
ROM: System Bootstrap, Version 11.0(10c), SOFTWARE
BOOTFLASH: 3000 Bootstrap Software (IGS-BOOT-R), Version 11.0(10c), RELEASE SOFTWARE (fc1)
LAB-R1 uptime is 3 hours, 8 minutes
System restarted by power-on
System image file is "flash:c2500-i-l_113-6.bin", booted via flash
cisco 2500 (68030) processor (revision N) with 14336K/2048K bytes of memory.
Processor board ID 05943495, with hardware revision 00000000
Bridging software.
X.25 software, Version 3.0.0.
1 Ethernet/IEEE 802.3 interface(s)
2 Serial network interface(s)
32K bytes of non-volatile configuration memory.
16384K bytes of processor board System flash (Read ONLY)
Configuration register is 0x2102

R2:

Cisco Internetwork Operating System Software
IOS (tm) 2500 Software (C2500-I-L), Experimental Version 12.3(20051208:143931) [
gkaruppu-geo-V123_16A-sc56019 102]
Copyright (c) 1986-2005 by cisco Systems, Inc.
Compiled Thu 08-Dec-05 20:11 by gkaruppu
Image text-base: 0x03060758, data-base: 0x00001000
ROM: System Bootstrap, Version 11.0(10c), SOFTWARE
BOOTLDR: 3000 Bootstrap Software (IGS-BOOT-R), Version 11.0(10c), RELEASE SOFTWA
RE (fc1)
LAB-R3 uptime is 1 hour, 53 minutes
System returned to ROM by power-on
System image file is "flash:c2500-i-l.geo-V123_16A-sc56019-vani"
cisco 2500 (68030) processor (revision N) with 14336K/2048K bytes of memory.
Processor board ID 05944203, with hardware revision 00000000
Bridging software.
X.25 software, Version 3.0.0.
1 Ethernet/IEEE 802.3 interface(s)
2 Serial network interface(s)
32K bytes of non-volatile configuration memory.
16384K bytes of processor board System flash (Read ONLY)
Configuration register is 0x2142

miller811

why ir R2 config register 0x2142

0x2142: NVRAM contents are bypassed, startup configuration is ignored.

beef1218

I can't tell where the problem is. Although the register 0x2142 needs to be fixed, it's not the reason of the connection failure.

Islander954

Changed the config register to 0x2102, erased sart up config, reloaded and cofigured with only basic conf. Still nada.

mikej412

Double check both R1 & R2 serial interfaces -- run the clockrate ? on both serial interfaces and make sure the speed you have configured on R2 is supported on both sides.

What IOS and what kind of router is R3? You mentioned it in an interface description on R2 -- it may be worth a try just to confirm you do have a couple of good serial ports somewhere, a good configuration, and a working cable.

If you can get a working serial connection with R3, then that narrows where the problem is between R1 & R2. Heck, try both R1 & R2 Serial 0 against R3 and see if 1 or both work then.

What do you have for the show interface command with PPP configured? Does it look like this?

Encapsulation PPP, loopback not set
Keepalive set (10 sec)
LCP Open
Open: IPCP, CDPCP

When HDLC didn't work -- how didn't it work? Same Serial Up but Line Protocol down? It's probably time to see the full "show interface serial 0" output and check out the statistics and status down at the bottom of the output.

Make sure your cables are firmly seated and screwed down. You may want to pull out the cable and double check that you haven't bent any pins.

Not sure what the "experimental" IOS is on R2.... may be worth a trip to the Cisco IOS Feature Navigator and confirm that PPP (and HDLC) existed back in the days of 11.3 (if the feature navigator goes back that far).

Kaminsky

Looking at your sh controllers it does suggest the cable is fine as one is showing DCE and the other is showing DTE. If there was a pin problem, I imagine all you would get there would be a "No Cable" message in the output.

The IP addresses seem fine with ip address 192.168.2.1 255.255.255.0 on serial 0 of Lab 1 and ip address 192.168.2.20 255.255.255.0 on serial 0 of Lab 2.

Might be something to do with the clock-rate but I imagine if that was too high, it would negotiate downward to something acceptable. Could check out the clock rate the 2501's can handle.

It may also be something to do with the version of IOS but before hunting that down, what does debug tell you what is going on with the communication across that link ?

> debug ppp negotiation
> debug ppp authentication

May be some clues as to what is going on in there.

Islander954

Thank you for all the good advice fellows.

There was nothing wrong with the configuration. I was just … BAD PORTS!! I use used routers from work for my lab. Some of them come back from the field with problems and are not properly labeled.

This was a good troubleshooting experience.

Thank to all.

miller811

Islander954 wrote: »

Thank you for all the good advice fellows.

There was nothing wrong with the configuration. I was just … BAD PORTS!! I use used routers from work for my lab. Some of them come back from the field with problems and are not properly labeled.

This was a good troubleshooting experience.

Thank to all.

now that is something you would have never learned if you did not have real gear....