Contents

Introduction
Before You Begin
     Conventions
     Prerequisites
     Components Used
     Background Theory
Configure
     Network Diagram
     Configurations
Verify
Troubleshoot
     Troubleshooting Procedure
     Troubleshooting Commands
Related Information

Introduction

The sample configurations in this document show how NxE1 links (with or without G.704 framing) can be bundled by means of a Multilink interface. The Multilink interface is introduced in Cisco IOS® Software Release 12.0(3)T for distributed Multilink Point to Point Protocol (PPP) on Cisco 7500 router Versatile Interface Processor (VIP)-based T1 or E1 interfaces (see Related Information below). It is supported for non-VIP based T1/E1 (and other WAN) interfaces since Cisco IOS Software Release 12.0(4)T.

Before You Begin

Conventions

For more information on document conventions, see the Cisco Technical Tips Conventions.

Prerequisites

Since Multilink PPP increases the CPU load, you are advised to:

1. Verify the current average CPU load before adding Multilink interfaces or adding E1 links to a Multilink interface.

2. Use distributed Multilink PPP on Cisco 7500 VIP-based platforms whenever possible. For more details on the restrictions and prerequisites of distributed Multilink PPP, please refer to the Cisco IOS Software Release 12.0(3)T New Feature Documenation (see Related Information below).

3. Disable Multilink PPP fragmentation whenever possible.

Note: This increases latency over the Multilink bundle.

Components Used

The information in this document is based on the software and hardware versions below.

• A Cisco 7505 router equipped with VIP2-50 and PA-MC-8E1 and running Cisco IOS Software Release 12.1(11a).

• A Cisco 7206 router equipped with PA-MC-8E1 and running Cisco IOS Software Release 12.1(11).

The information presented in this document was created from devices in a specific lab environment. All of the devices used in this document started with a cleared (default) configuration. If you are working in a live network, ensure that you understand the potential impact of any command before using it.

Background Theory

Multilink PPP, standardized in Request for Comments (RFC) 1990, is similar to load balancing techniques in that it sends packets across the individual links in a round robin fashion. However, Multilink PPP adds three significant capabilities.

• Firstly, because multilane PPP works at the link layer, it makes an NxT1/E1 bundle appear as one logical link to the upper layer protocols in the router. Thus, only one network address needs to be configured for the entire NxT1/E1 bundle.

• Secondly, Multilink PPP keeps track of packet sequencing and buffers packets that arrive early. With this ability, Multilink PPP preserves packet order across the entire NxT1/E1 bundle.

• Thirdly, packet fragmentation can be enabled to split large data packets into smaller packet fragments that are individually transmitted across the links. In many circumstances, fragmentation can increase the efficiency of the NxT1/E1 link.

Multilink PPP also offers significant link manageability. If an individual link fails, Multilink PPP can automatically detect the failure and remove that link from the bundle. As long as one link of the bundle is working the logical interface representing the bundle is up. By using keep alive signals, Multilink PPP can detect when a previously failed link comes back up then reinsert that link into the bundle. Additionally, when more bandwidth is needed, additional links can be added to the bundle by simply configuring them as a member of the bundle. No reconfiguration at the network layer, such as new addressing, is needed. This is also a significant factor when considering the use of advanced router services. A specific quality of service, for example, can be configured once for the bundle as a whole rather than on each link in the bundle.

The trade-off for the increased functionality is that Multilink PPP requires greater CPU processing than load balancing solutions. Packet reordering, fragment reassembly, and the Multilink PPP protocol itself increases the CPU load.

For a detailed description and comparison of alternatives for high bandwidth connections using parallel E1 links, please refer to the White Paper on Alternatives for High Bandwidth Connections Using Parallel T1/E1 Links..

Configure

In this section, you are presented with the information to configure the features described in this document.

Note: To find additional information on the commands used in this document, use the Command Lookup Tool (registered customers only) .

Network Diagram

This document uses the network setup shown in the diagram below.

Configurations

This document uses the configurations shown below.

E1 Links With G.704 Framing(Cisco 7505)
version 12.1
service timestamps debug datetime msec
service timestamps log datetime msec
no service password-encryption
!
hostname diana
!
enable password
!
username bob password 0 mlppp

!--- optional CHAP secret shared with remote router

!
!
!
ip subnet-zero
ip cef distributed

!--- mandatory command for distributed Multilink PPP

!
no ip domain-lookup
!
!
controller E1 1/0/0
 channel-group 0 timeslots 1-31

!--- all timeslots must be assigned to one channel-group
 
!
controller E1 1/0/1
 channel-group 0 timeslots 1-31

!--- all timeslots must be assigned to one channel-group

!
controller E1 1/0/2
 channel-group 0 timeslots 1-31

!--- all timeslots must be assigned to one channel-group

!
controller E1 1/0/3
 channel-group 0 timeslots 1-31

!--- all timeslots must be assigned to one channel-group

!
controller E1 1/0/4
 channel-group 0 timeslots 1-31

!--- all timeslots must be assigned to one channel-group

!
controller E1 1/0/5
 channel-group 0 timeslots 1-31

!--- all timeslots must be assigned to one channel-group

!
controller E1 1/0/6
 channel-group 0 timeslots 1-31

!--- all timeslots must be assigned to one channel-group

!
controller E1 1/0/7
 channel-group 0 timeslots 1-31

!--- all timeslots must be assigned to one channel-group

!
!
interface Multilink1
 ip address 10.10.10.1 255.255.255.0
 no cdp enable
 ppp multilink
 no ppp multilink fragmentation
 
!--- optional command to reduce CPU load

 multilink-group 1
!
interface Serial1/0/0:0
 no ip address
 ip route-cache distributed

!---default and mandatory command for distributed Multilink PPP

encapsulation ppp
 tx-queue-limit 26
 ppp authentication chap
 
!--- optional command needed when interfacing to non-Cisco router

 ppp multilink
 multilink-group 1
!
interface Serial1/0/1:0
 no ip address
 ip route-cache distributed
 
!---default and mandatory command for distributed Multilink PPP

 encapsulation ppp
 tx-queue-limit 26
 ppp authentication chap
 
!--- optional command needed when interfacing to non-Cisco router

ppp multilink
 multilink-group 1
!
interface Serial1/0/2:0
 no ip address
 ip route-cache distributed

 !---default and mandatory command for distributed Multilink PPP
 
encapsulation ppp
 tx-queue-limit 26
 ppp authentication chap

 !--- optional command needed when interfacing to non-Cisco router

 ppp multilink
 multilink-group 1
!
interface Serial1/0/3:0
 no ip address
 ip route-cache distributed
 
!---default and mandatory command for distributed Multilink PPP

encapsulation ppp
 tx-queue-limit 26
 ppp authentication chap
 
!--- optional command needed when interfacing to non-Cisco router

 ppp multilink
 multilink-group 1
!
interface Serial1/0/4:0
 no ip address
 ip route-cache distributed
 
!---default and mandatory command for distributed Multilink PPP

encapsulation ppp
 tx-queue-limit 26
 ppp authentication chap
 
!--- optional command needed when interfacing to non-Cisco router

 ppp multilink
 multilink-group 1
!
interface Serial1/0/5:0
 no ip address
 ip route-cache distributed
 
!---default and mandatory command for distributed Multilink PPP

encapsulation ppp
 tx-queue-limit 26
 ppp authentication chap
 
!--- optional command needed when interfacing to non-Cisco router

 ppp multilink
 multilink-group 1
!
interface Serial1/0/6:0
 no ip address
 ip route-cache distributed

 !---default and mandatory command for distributed Multilink PPP

 encapsulation ppp
 tx-queue-limit 26
 ppp authentication chap

 !--- optional command needed when interfacing to non-Cisco router

 ppp multilink
 multilink-group 1
!
interface Serial1/0/7:0
 no ip address
 ip route-cache distributed
 
!---default and mandatory command for distributed Multilink PPP

 encapsulation ppp
 tx-queue-limit 26
 ppp authentication chap
 
!--- optional command needed when interfacing to non-Cisco router

 ppp multilink
 multilink-group 1
!
interface Ethernet1/1/0
 ip address 10.10.20.1 255.255.255.0
 no cdp enable
!
ip classless
ip route 10.10.30.0 255.255.255.0 10.10.10.2
no ip http server
!
!
line con 0
 exec-timeout 0 0
line aux 0
line vty 0 4
 exec-timeout 0 0
 password
 login
!
end

(Cisco 7206)
version 12.1
service timestamps debug datetime msec
service timestamps log datetime msec
no service password-encryption
!
hostname bob
!
enable password
!
username diana password 0 mlppp

!--- optional CHAP secret shared with remote router

!
!
!
ip subnet-zero
!
!
controller E1 3/0
 clock source internal
 channel-group 0 timeslots 1-31

!--- all timeslots must be assigned to one channel-group

!
controller E1 3/1
 clock source internal

 !--- only required when providing master clock to remote router
 
 channel-group 0 timeslots 1-31

!--- all timeslots must be assigned to one channel-group

!
controller E1 3/2
 clock source internal

 !--- only required when providing master clock to remote router

 channel-group 0 timeslots 1-31

!--- all timeslots must be assigned to one channel-group

!
controller E1 3/3
 clock source internal

 !--- only required when providing master clock to remote router

 channel-group 0 timeslots 1-31

!--- all timeslots must be assigned to one channel-group

!
controller E1 3/4
 clock source internal

 !--- only required when providing master clock to remote router

 channel-group 0 timeslots 1-31

!--- all timeslots must be assigned to one channel-group

!
controller E1 3/5
 clock source internal
 
!--- only required when providing master clock to remote router

 channel-group 0 timeslots 1-31

!--- all timeslots must be assigned to one channel-group

!
controller E1 3/6
 clock source internal
 
!--- only required when providing master clock to remote router

 channel-group 0 timeslots 1-31

!--- all timeslots must be assigned to one channel-group

!
controller E1 3/7
 clock source internal
 
!--- only required when providing master clock to remote router

 channel-group 0 timeslots 1-31

!--- all timeslots must be assigned to one channel-group

!
!
!
!
!
interface Multilink1
 ip address 10.10.10.2 255.255.255.0
 ppp multilink
 no ppp multilink fragmentation
 !--- optional command to reduce CPU load
 multilink-group 1
!
interface FastEthernet0/0
 ip address 10.10.30.1 255.255.255.0
 no ip route-cache
 no ip mroute-cache
 half-duplex
 no cdp enable
!
interface Serial3/0:0
 no ip address
 encapsulation ppp
 no fair-queue
 ppp authentication chap

 !--- optional command needed when interfacing to non-Cisco router

 ppp multilink
 multilink-group 1
!
interface Serial3/1:0
 no ip address
 encapsulation ppp
 no fair-queue
 ppp authentication chap
 
!--- optional command needed when interfacing to non-Cisco router

 ppp multilink
 multilink-group 1
!
interface Serial3/2:0
 no ip address
 encapsulation ppp
 no fair-queue
 ppp authentication chap
 
!--- optional command needed when interfacing to non-Cisco router

 ppp multilink
 multilink-group 1
!
interface Serial3/3:0
 no ip address
 encapsulation ppp
 no fair-queue
 ppp authentication chap
 
!--- optional command needed when interfacing to non-Cisco router

 ppp multilink
 multilink-group 1
!
interface Serial3/4:0
 no ip address
 encapsulation ppp
 no fair-queue
 ppp authentication chap
 
!--- optional command needed when interfacing to non-Cisco router

 ppp multilink
 multilink-group 1
!
interface Serial3/5:0
 no ip address
 encapsulation ppp
 no fair-queue
 ppp authentication chap
 
!--- optional command needed when interfacing to non-Cisco router

 ppp multilink
 multilink-group 1
!
interface Serial3/6:0
 no ip address
 encapsulation ppp
 no fair-queue
 ppp authentication chap

 !--- optional command needed when interfacing to non-Cisco router

 ppp multilink
 multilink-group 1
!
interface Serial3/7:0
 no ip address
 encapsulation ppp
 no fair-queue
 ppp authentication chap
 
!--- optional command needed when interfacing to non-Cisco router

 ppp multilink
 multilink-group 1
!
ip classless
ip route 10.10.20.0. 255.255.255.0 10.10.10.1
no ip http server
!
!
line con 0
 exec-timeout 0 0
line aux 0
line vty 0 4
 exec-timeout 0 0
 password
 login
!
end


E1 Links With No G.704 Framing
(Cisco 7505)
version 12.1
service timestamps debug datetime msec
service timestamps log datetime msec
no service password-encryption
!
hostname diana
!
enable password
!
!
!
!
!
ip subnet-zero
ip cef distributed

!--- mandatory command for distributed Multilink PPP

no ip domain-lookup
!
!
controller E1 0/1/0
 channel-group 0 unframed
!
controller E1 0/1/1
 channel-group 0 unframed
!
controller E1 0/1/2
 channel-group 0 unframed
!
controller E1 0/1/3
 channel-group 0 unframed
!
controller E1 0/1/4
 channel-group 0 unframed
!
controller E1 0/1/5
 channel-group 0 unframed
!
controller E1 0/1/6
 channel-group 0 unframed
!
controller E1 0/1/7
 channel-group 0 unframed
!
!
!
interface Multilink1
 ip address 10.10.10.1 255.255.255.0
 no cdp enable
 ppp multilink
 no ppp multilink fragmentation
 
!--- optional command to reduce CPU load

 multilink-group 1
!
interface Serial0/1/0:0
 no ip address
 ip route-cache distributed

 !---default and mandatory command for distributed Multilink PPP

 encapsulation ppp
 tx-queue-limit 26
 no fair-queue
 ppp multilink
 multilink-group 1
!
interface Serial0/1/1:0
 no ip address
 ip route-cache distributed

 !---default and mandatory command for distributed Multilink PPP

 encapsulation ppp
 tx-queue-limit 26
 no fair-queue
 ppp multilink
 multilink-group 1
!
interface Serial0/1/2:0
 no ip address
 ip route-cache distributed
 
!---default and mandatory command for distributed Multilink PPP

 encapsulation ppp
 tx-queue-limit 26
 no fair-queue
 ppp multilink
 multilink-group 1
!
interface Serial0/1/3:0
 no ip address
 ip route-cache distributed
 
!---default and mandatory command for distributed Multilink PPP

 encapsulation ppp
 tx-queue-limit 26
 no fair-queue
 ppp multilink
 multilink-group 1
!
interface Serial0/1/4:0
 no ip address
 ip route-cache distributed
 
!---default and mandatory command for distributed Multilink PPP

 encapsulation ppp
 tx-queue-limit 26
 no fair-queue
 ppp multilink
 multilink-group 1
!
interface Serial0/1/5:0
 no ip address
 ip route-cache distributed

 !---default and mandatory command for distributed Multilink PPP

 encapsulation ppp
 tx-queue-limit 26
 no fair-queue
 ppp multilink
 multilink-group 1
!
interface Serial0/1/6:0
 no ip address
 ip route-cache distributed

 !---default and mandatory command for distributed Multilink PPP

 encapsulation ppp
 tx-queue-limit 26
 no fair-queue
 ppp multilink
 multilink-group 1
!
interface Serial0/1/7:0
 no ip address
 ip route-cache distributed

 !---default and mandatory command for distributed Multilink PPP

 encapsulation ppp
 tx-queue-limit 26
 no fair-queue
 ppp multilink
 multilink-group 1
!
interface Ethernet1/1/0
 ip address 10.10.20.1 255.255.255.0
 no cdp enable
!
ip classless
ip route 10.10.30.0 255.255.255.0 10.10.10.2
no ip http server
!
!
line con 0
 exec-timeout 0 0
line aux 0
line vty 0 4
 exec-timeout 0 0
 password
 login
!
end


(Cisco 7206）
version 12.1
service timestamps debug datetime msec
service timestamps log datetime msec
no service password-encryption
!
hostname bob
!
enable password
!
!
!
!
!
ip subnet-zero  !
controller E1 3/0
 clock source internal

 !--- only required when providing master clock to remote router

 channel-group 0 unframed
!
controller E1 3/1
 clock source internal
 
!--- only required when providing master clock to remote router

 channel-group 0 unframed
!
controller E1 3/2
 clock source internal
 
!--- only required when providing master clock to remote router

 channel-group 0 unframed
!
controller E1 3/3
 clock source internal
 
!--- only required when providing master clock to remote router

 channel-group 0 unframed
!
controller E1 3/4
 clock source internal

 !--- only required when providing master clock to remote router

 channel-group 0 unframed
!
controller E1 3/5
 clock source internal
 
!--- only required when providing master clock to remote router

 channel-group 0 unframed
!
controller E1 3/6
 clock source internal
 
!--- only required when providing master clock to remote router

 channel-group 0 unframed
!
controller E1 3/7
 clock source internal
 
!--- only required when providing master clock to remote router

 channel-group 0 unframed
!
!
!
!
!
interface Multilink1
 ip address 10.10.10.2 255.255.255.0
 ppp multilink
 no ppp multilink fragmentation

 !--- optional command to reduce CPU load

 multilink-group 1
!
interface FastEthernet0/0
 ip address 10.10.30.1 255.255.255.0
 no ip route-cache
 no ip mroute-cache
 half-duplex
 no cdp enable
!
interface Serial3/0:0
 no ip address
 encapsulation ppp
 no fair-queue
 ppp multilink
 multilink-group 1
!
interface Serial3/1:0
 no ip address
 encapsulation ppp
 no fair-queue
 ppp multilink
 multilink-group 1
!
interface Serial3/2:0
 no ip address
 encapsulation ppp
 no fair-queue
 ppp multilink
 multilink-group 1
!
interface Serial3/3:0
 no ip address
 encapsulation ppp
 no fair-queue
 ppp multilink
 multilink-group 1
!
interface Serial3/4:0
 no ip address
 encapsulation ppp
 no fair-queue
 ppp multilink
 multilink-group 1
!
interface Serial3/5:0
 no ip address
 encapsulation ppp
 no fair-queue
 ppp multilink
 multilink-group 1
!
interface Serial3/6:0
 no ip address
 encapsulation ppp
 no fair-queue
 ppp multilink
 multilink-group 1
!
interface Serial3/7:0
 no ip address
 encapsulation ppp
 no fair-queue
 ppp multilink
 multilink-group 1
!
ip classless
ip route 10.10.20.0 255.255.255.0 10.10.10.1
no ip http server
!
!
line con 0
 exec-timeout 0 0
line aux 0
line vty 0 4
 exec-timeout 0 0
 password
 login
!
end

Verify
This section provides information you can use to confirm your configuration is working properly.

Certain show commands are supported by the Output Interpreter Tool (registered customers only) , which allows you to view an analysis of show command output.

show ppp multilink - Shows all Multilink bundles, together with all Multilink bundle members.

show interfaces multilink - Shows the status of the Multilink bundle.

show interfaces serial - Shows the status of each Multilink bundle member.

show controllers e1 - Shows the status of each E1 link.

Troubleshoot
This section provides information you can use to troubleshoot your configuration.

Troubleshooting Procedure
Below is troubleshooting information relevant to both configurations.

Verify the status of the Multilink interface with show interface multilink:

If the Multilink interface is down, then verify the status of all Multilink bundle members with show ppp multilink

If the Multilink line protocol is down, then verify the Network Control Protocol (NCP) and Multilink PPP (MLP) messages with debug ppp negotiation and debug ppp multilink events

If a Multilink member is inactive, verify the status of the Serial interface with show interface serial:

If the Serial interface is down, verify the status of the corresponding E1 link with show controller e1

If the Serial line protocol is down, verify the Link Control Protocol (LCP) and Challenge Handshake Authentication Protocol (CHAP) messages with debug ppp negotiation and debug ppp authentication

Troubleshooting Commands
Certain show commands are supported by the Output Interpreter Tool (registered customers only) , which allows you to view an analysis of show command output.

Note: Before issuing debug commands, please see Important Information on Debug Commands.

show ppp multilink - Shows all Multilink bundles, together with all Multilink bundle members.

show interfaces multilink - Shows the status of the Multilink bundle.

show interfaces serial - Shows the status of each Multilink bundle member.

show controllers e1 - Shows the status of each E1 link.

debug ppp negotiation - Shows all LCP and NCP negotiation messages.

debug ppp authentication (optional) - Shows all CHAP authentication messages.

debug ppp multilink events - Shows all MLP bundle events.

Following example shows the output of the troubleshooting commands on the Cisco 7505 for the first configuration example.

All eight E1 links are active:

diana#show ppp multilink  Multilink1, bundle name is bob
  Bundle up for 00:05:35
  Bundle is Distributed
  0 lost fragments, 0 reordered, 0 unassigned
  0 discarded, 0 lost received, 3/255 load
  0x1226 received sequence, 0x1226 sent sequence
  Member links: 8 active, 0 inactive (max not set, min not set)
    Serial1/0/0:0, since 00:05:35, no frags rcvd
    Serial1/0/1:0, since 00:05:35, no frags rcvd
    Serial1/0/2:0, since 00:05:35, no frags rcvd
    Serial1/0/3:0, since 00:05:35, no frags rcvd
    Serial1/0/4:0, since 00:05:35, no frags rcvd
    Serial1/0/5:0, since 00:05:35, no frags rcvd
    Serial1/0/6:0, since 00:05:35, no frags rcvd
    Serial1/0/7:0, since 00:05:35, no frags rcvd  diana#show interface multilink 1
Multilink1 is up, line protocol is up
  Hardware is multilink group interface
  Internet address is 10.10.10.1/24
  MTU 1500 bytes, BW 15872 Kbit, DLY 100000 usec,
     reliability 255/255, txload 3/255, rxload 3/255
  Encapsulation PPP, loopback not set
  Keepalive set (10 sec)
  DTR is pulsed for 2 seconds on reset
  LCP Open, multilink Open
  Open: IPCP
  Last input 00:00:00, output never, output hang never
  Last clearing of "show interface" counters 00:06:39
  Input queue: 1/75/0/0 (size/max/drops/flushes); Total output drops: 0
  Queueing strategy: fifo
  Output queue :0/40 (size/max)
  5 minute input rate 241000 bits/sec, 28 packets/sec
  5 minute output rate 241000 bits/sec, 28 packets/sec
     6525 packets input, 9810620 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
     6526 packets output, 9796112 bytes, 0 underruns
     0 output errors, 0 collisions, 0 interface resets
     0 output buffer failures, 0 output buffers swapped out
     0 carrier transitions  
Here, the E1 controller 3/0 on the Cisco 7206 is disabled, causing the E1 controller 1/0/0 and Serial 1/0/0:0 on the Cisco 7505 to go down:

diana#
*Nov 23 12:52:54.167: %CONTROLLER-5-UPDOWN:
Controller E1 1/0/0, changed state to down
*Nov 23 12:52:56.171: %LINK-3-UPDOWN:
Interface Serial1/0/0:0, changed state to down
*Nov 23 12:52:57.171: %LINEPROTO-5-UPDOWN:
Line protocol on Interface Serial1/0/0:0, changed state to down  diana#show ppp multilink
Multilink1, bundle name is bob
  Bundle up for 00:06:52
  Bundle is Distributed
  0 lost fragments, 0 reordered, 0 unassigned
  0 discarded, 0 lost received, 1/255 load
  0x269C received sequence, 0x269B sent sequence
  Member links: 7 active, 1 inactive (max not set, min not set)
    Serial1/0/1:0, since 00:06:52, no frags rcvd
    Serial1/0/2:0, since 00:06:52, no frags rcvd
    Serial1/0/3:0, since 00:06:52, no frags rcvd
    Serial1/0/4:0, since 00:06:52, no frags rcvd
    Serial1/0/5:0, since 00:06:52, no frags rcvd
    Serial1/0/6:0, since 00:06:52, no frags rcvd
    Serial1/0/7:0, since 00:06:52, no frags rcvd
    Serial1/0/0:0 (inactive)  diana#show interface multilink 1
Multilink1 is up, line protocol is up
  Hardware is multilink group interface
  Internet address is 10.10.10.1/24
  MTU 1500 bytes, BW 13888 Kbit, DLY 100000 usec,
     reliability 255/255, txload 6/255, rxload 6/255
  Encapsulation PPP, loopback not set
  Keepalive set (10 sec)
  DTR is pulsed for 2 seconds on reset
  LCP Open, multilink Open
  Open: IPCP
  Last input 00:00:00, output never, output hang never
  Last clearing of "show interface" counters 00:07:47
  Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0
  Queueing strategy: fifo
  Output queue :0/40 (size/max)
  5 minute input rate 367000 bits/sec, 40 packets/sec
  5 minute output rate 367000 bits/sec, 40 packets/sec
     10899 packets input, 16389116 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
     10901 packets output, 16367362 bytes, 0 underruns
     0 output errors, 0 collisions, 0 interface resets
     0 output buffer failures, 0 output buffers swapped out
     0 carrier transitions  diana#show interface serial 1/0/0:0
Serial1/0/0:0 is down, line protocol is down
  Hardware is Multichannel E1
  MTU 1500 bytes, BW 1984 Kbit, DLY 20000 usec,
     reliability 255/255, txload 41/255, rxload 41/255
  Encapsulation PPP, crc 16, Data non-inverted
  Keepalive set (10 sec)
  LCP Closed, multilink Closed
  Closed: CDPCP
  Last input 00:00:15, output 00:00:17, output hang never
  Last clearing of "show interface" counters 00:07:42
  Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0
  Queueing strategy: fifo
  Output queue :0/40 (size/max)
  5 minute input rate 323000 bits/sec, 35 packets/sec
  5 minute output rate 324000 bits/sec, 35 packets/sec
     9811 packets input, 14623345 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
     9809 packets output, 14680161 bytes, 0 underruns
     0 output errors, 0 collisions, 1 interface resets
     0 output buffer failures, 0 output buffers swapped out
     2 carrier transitions alarm present
  Timeslot(s) Used:1-31, subrate: 64Kb/s, transmit delay is 0 flags
  Transmit queue length 26  diana#show controller e1
E1 1/0/0 is down.
  Applique type is Channelized E1 - balanced
  Transmitter is sending remote alarm.
  Receiver is getting AIS.
  Framing is CRC4, Line Code is HDB3, Clock Source is Line.
  International Bit: 1, National Bits: 11111
  Data in current interval (465 seconds elapsed):
     1 Line Code Violations, 1 Path Code Violations
     0 Slip Secs, 0 Fr Loss Secs, 1 Line Err Secs, 0 Degraded Mins
     0 Errored Secs, 0 Bursty Err Secs, 0 Severely Err Secs, 19 Unavail Secs
...  diana#debug ppp negotiation
 PPP protocol negotiation debugging is on  diana#debug ppp authentication
PPP authentication debugging is on  diana#debug ppp multilink events
Multilink events debugging is on
Here, the E1 controller 3/0 on the Cisco 7206 is enabled again

diana#
*Nov 23 12:53:40.167: %CONTROLLER-5-UPDOWN: Controller E1 1/0/0, changed state to up
*Nov 23 12:53:42.071: Se1/0/0:0 LCP: I CONFREQ [Closed] id 34 len 26
*Nov 23 12:53:42.071: Se1/0/0:0 LCP:    AuthProto CHAP (0x0305C22305)
*Nov 23 12:53:42.071: Se1/0/0:0 LCP:    MagicNumber 0x10193C10 (0x050610193C10)
*Nov 23 12:53:42.071: Se1/0/0:0 LCP:    MRRU 1524 (0x110405F4)
*Nov 23 12:53:42.071: Se1/0/0:0 LCP:    EndpointDisc 1 Local (0x130701646F6469)
*Nov 23 12:53:42.071: Se1/0/0:0 LCP: Lower layer not up, Fast Starting
*Nov 23 12:53:42.071: Se1/0/0:0 PPP: Treating connection as a dedicated line
*Nov 23 12:53:42.071: Se1/0/0:0 PPP: Phase is ESTABLISHING, Active Open
*Nov 23 12:53:42.071: Se1/0/0:0 LCP: O CONFREQ [Closed] id 2 len 27
*Nov 23 12:53:42.071: Se1/0/0:0 LCP:    AuthProto CHAP (0x0305C22305)
*Nov 23 12:53:42.071: Se1/0/0:0 LCP:    MagicNumber 0x80248196 (0x050680248196)
*Nov 23 12:53:42.071: Se1/0/0:0 LCP:    MRRU 1524 (0x110405F4)
*Nov 23 12:53:42.071: Se1/0/0:0 LCP:    EndpointDisc 1 Local (0x1308016469616E61)
*Nov 23 12:53:42.071: Se1/0/0:0 LCP: O CONFACK [REQsent] id 34 len 26
*Nov 23 12:53:42.075: Se1/0/0:0 LCP:    AuthProto CHAP (0x0305C22305)
*Nov 23 12:53:42.075: Se1/0/0:0 LCP:    MagicNumber 0x10193C10 (0x050610193C10)
*Nov 23 12:53:42.075: Se1/0/0:0 LCP:    MRRU 1524 (0x110405F4)
*Nov 23 12:53:42.075: Se1/0/0:0 LCP:    EndpointDisc 1 Local (0x130701646F6469)
*Nov 23 12:53:42.075: Se1/0/0:0 LCP: I CONFACK [ACKsent] id 2 len 27
*Nov 23 12:53:42.075: Se1/0/0:0 LCP:    AuthProto CHAP (0x0305C22305)
*Nov 23 12:53:42.075: Se1/0/0:0 LCP:    MagicNumber 0x80248196 (0x050680248196)
*Nov 23 12:53:42.075: Se1/0/0:0 LCP:    MRRU 1524 (0x110405F4)
*Nov 23 12:53:42.075: Se1/0/0:0 LCP:    EndpointDisc 1 Local (0x1308016469616E61)
*Nov 23 12:53:42.075: Se1/0/0:0 LCP: State is Open
*Nov 23 12:53:42.079: Se1/0/0:0 PPP: Phase is AUTHENTICATING, by both
*Nov 23 12:53:42.079: Se1/0/0:0 CHAP: O CHALLENGE id 2 len 26 from "diana"
*Nov 23 12:53:42.079: Se1/0/0:0 CHAP: I CHALLENGE id 4 len 25 from "bob"
*Nov 23 12:53:42.079: Se1/0/0:0 CHAP: O RESPONSE id 4 len 26 from "diana"
*Nov 23 12:53:42.079: %LINK-3-UPDOWN: Interface Serial1/0/0:0, changed state to up
*Nov 23 12:53:42.083: Se1/0/0:0 CHAP: I RESPONSE id 2 len 25 from "bob"
*Nov 23 12:53:42.083: Se1/0/0:0 CHAP: I SUCCESS id 4 len 4
*Nov 23 12:53:42.083: Se1/0/0:0 CHAP: O SUCCESS id 2 len 4
*Nov 23 12:53:42.087: Se1/0/0:0 MLP: Request add link to bundle
*Nov 23 12:53:42.087: Se1/0/0:0 PPP: Phase is VIRTUALIZED
*Nov 23 12:53:42.087: Se1/0/0:0 MLP: Adding link to bundle
*Nov 23 12:53:42.087: Mu1 MLP: Added link Se1/0/0:0 to bundle bob
*Nov 23 12:53:43.087: %LINEPROTO-5-UPDOWN:
Line protocol on Interface Serial1/0/0:0, changed state to up  diana#show ppp multilink
Multilink1, bundle name is bob
  Bundle up for 00:07:46
  Bundle is Distributed
  0 lost fragments, 0 reordered, 0 unassigned
  0 discarded, 0 lost received, 7/255 load
  0x35BF received sequence, 0x35BE sent sequence
  Member links: 8 active, 0 inactive (max not set, min not set)
    Serial1/0/1:0, since 00:07:46, no frags rcvd
    Serial1/0/2:0, since 00:07:46, no frags rcvd
    Serial1/0/3:0, since 00:07:46, no frags rcvd
    Serial1/0/4:0, since 00:07:46, no frags rcvd
    Serial1/0/5:0, since 00:07:46, no frags rcvd
    Serial1/0/6:0, since 00:07:46, no frags rcvd
    Serial1/0/7:0, since 00:07:46, no frags rcvd
    Serial1/0/0:0, since 00:00:13, no frags rcvd  diana#show interface multilink 1
Multilink1 is up, line protocol is up
  Hardware is multilink group interface
  Internet address is 10.10.10.1/24
  MTU 1500 bytes, BW 15872 Kbit, DLY 100000 usec,
     reliability 255/255, txload 7/255, rxload 7/255
  Encapsulation PPP, loopback not set
  Keepalive set (10 sec)
  DTR is pulsed for 2 seconds on reset
  LCP Open, multilink Open
  Open: IPCP
  Last input 00:00:00, output never, output hang never
  Last clearing of "show interface" counters 00:08:32
  Input queue: 1/75/0/0 (size/max/drops/flushes); Total output drops: 0
  Queueing strategy: fifo
  Output queue :0/40 (size/max)
  5 minute input rate 443000 bits/sec, 49 packets/sec
  5 minute output rate 443000 bits/sec, 49 packets/sec
     14098 packets input, 21200412 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
     14099 packets output, 21170758 bytes, 0 underruns
     0 output errors, 0 collisions, 0 interface resets
     0 output buffer failures, 0 output buffers swapped out
     0 carrier transitions  diana#show interface serial 1/0/0:0
Serial1/0/0:0 is up, line protocol is up
  Hardware is Multichannel E1
  MTU 1500 bytes, BW 1984 Kbit, DLY 20000 usec,
     reliability 255/255, txload 32/255, rxload 32/255
  Encapsulation PPP, crc 16, Data non-inverted
  Keepalive set (10 sec)
  LCP Open, multilink Open
  Last input 00:00:02, output 00:00:02, output hang never
  Last clearing of "show interface" counters 00:08:39
  Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0
  Queueing strategy: fifo
  Output queue :0/40 (size/max)
  5 minute input rate 253000 bits/sec, 24 packets/sec
  5 minute output rate 254000 bits/sec, 24 packets/sec
     9821 packets input, 14623552 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
     9819 packets output, 14680370 bytes, 0 underruns
     0 output errors, 0 collisions, 1 interface resets
     0 output buffer failures, 0 output buffers swapped out
     3 carrier transitions no alarm present
  Timeslot(s) Used:1-31, subrate: 64Kb/s, transmit delay is 0 flags
  Transmit queue length 26  diana#show controller e1
E1 1/0/0 is up.
  Applique type is Channelized E1 - balanced
  No alarms detected.
  Framing is CRC4, Line Code is HDB3, Clock Source is Line.
  International Bit: 1, National Bits: 11111
  Data in current interval (519 seconds elapsed):
     1 Line Code Violations, 1 Path Code Violations
     0 Slip Secs, 0 Fr Loss Secs, 1 Line Err Secs, 0 Degraded Mins
     0 Errored Secs, 0 Bursty Err Secs, 0 Severely Err Secs, 37 Unavail Secs