The 7th chapter deals with serial line and Frame Relay connection failures
I. Handling serial LINE faults
1. HDLC Encapsulation
High-level Data Link Control (HDLC) is a encapsulation method for a serial link, and HDLC is the default encapsulation method for the Cisco router serial interface.
The first step in dealing with a serial link failure is to look at both ends of the link to use the same package type.
Show interface serial 1; viewing interface information
Clear counters serial number; Reset interface counter to 0
Normally, both the interface and the line are up.
Cable failure, carrier failure, and hardware failure can all lead to an interface down, verifying the cable connection, replacing the hardware (including the cable), and checking the carrier signaling location problem.
Interface Up,line DOWN:CSU/DSU fault, router interface problem, CSU/DSU or carrier time inconsistency, no keepalive signaling, carrier problem received from the remote router. The configuration of the local interface and the remote interface should be verified.
Reason for interface restart:
? Packets queued within a few seconds are not sent;
? Hardware problems (Router interface, cable, CSU/DSU);
? Inconsistent clock signaling
? Loop interface
? Interface off
? Line protocol down and the interface is periodically restarted
Show controllers serial 0; show interface status, whether wired cable, clock rate
Show buffers; View system buffer pool, interface buffer settings
Debug serial interface; display HDLC or Frame Relay communication information
2. CSU/DSU Loop Test
There are four types of loop tests:
? Test the local loop on the local CSU/DSU;
? Test the local loop on the remote CSU/DSU;
? Test the remote loop from the local NIU to the remote CSU/DSU;
? The remote loop is tested from the remote NIU to the local CSU/DSU;
PPP uses the negotiated magic number to detect the loopback network with a PPP-encapsulated serial link.
3, the Serial line summary:
1) Symptoms and problems:
Symptoms or situation problems
Interface is administratively down;line protocol are down 1) the interface is closed from the command line 2) does not allow duplicate IP addresses, two interfaces using the same IP address will be down
Interface is Down;line protocol was down 1) unqualified cable 2) No local provider signaling 3) hardware failure (interface or CSU/DSU, cable) 4) clock
Interface is Up;line protocol was down 1) Not configured interface: local or remote 2) local provider Issue 3) keepalive serial number did not increase 4) hardware failure (local or remote interface, CSU/DSU) 5) line murmur 6) clock inconsistency 7) 2nd tier (e.g. LMI)
Interface is Up;line protocol was up (looped) link in a loop somewhere
Incrementing carrier transition counter 1) signal instability from the local provider 2) cable failure 3) hardware failure
Incrementing interface resets 1) cable failure, resulting in loss of CD signal 2) hardware failure 3) line congestion
Input Drops,errors,crc,and Framing Errors 1) line rate exceeds interface capacity 2) local provider problem 3) line murmur 4) cable failure 5) Unqualified cable 6) hardware failure
Output drops interface transmission capability exceeds line rate
2) Questions and actions
Problem-Solving Action programme
Local provider Issue 1) Check the CSU/DSU CD signal and other signals to see if the link is sending and receiving information 2) if there is no CD signal or other problems, contact your local provider to handle the failure
Defective or faulty cable 1) Use the cable that meets the requirements of the equipment 2) to switch the fault cable by using the breakout box Check 3)
Not configured interface 1) Use the show Running-config Check Interface configuration 2) Verify that the same package type is used on both ends of the link
KeepAlive Issue 1) Verify KeepAlive was sent 2) configured keepalive send, Debug keepalive3) Verify serial number increases 4) If serial number does not increase, run Loop Test 5) CSU/DSU loop, serial number is still not increased, then hardware failure
Hardware failure 1) hardware replacement
interface in loop mode 1) Check the interface configuration 2) if the interface is configured with a loop, remove 3) If the interface configuration is cleared, clear CSU/DSU loop mode 4) as CSU/DSU is not in loop mode, may be a provider ring
Interface administratively down 1) Check for duplicate IP address 2) for interface configuration mode, perform no shutdown
Line rate greater than interface capacity 1) use Hold-queue to reduce incoming queue size 2) increase the output queue size
Interface rate greater than line rate 1) reduce broadcast traffic 2) increase the output of queue 3) if necessary, use the queue algorithm
Second, handle the frame relay fault
DLCI is used to identify virtual links in frame Relay, DLCI is only local signaling, DLCI maps to 3rd IP addresses.
Steps to handle Frame relay:
1) Check the physical layer, cable or interface problems;
2) Check the interface encapsulation;
3) Check the type of LMI;
4) Check the mapping of DLCI to IP;
5) Verify the PVC of frame delay;
6) Verify the LMI of frame delay;
7) Check frame delay mapping;
8) check loop test;
1. Show command for Frame Relay
Show interface
Show Frame-relay LMI; display LMI-related information (LMI type, update, status)
Show Frame-relay PVC, output PVC information, LMI status for each DLCI 、... ）
Show Frame-relay map; provides DLCI information and encapsulation of all FR interfaces
2. Debug command for Frame Relay
Debug Frame-relay lmi; show LMI exchange information
Debug Frame-relay events; Show protocols and applications use DLCI details
3, Frame Relay total NA
1) Symptoms and problems
Symptoms or situation-related issues
Frame realy link is down 1) cable failure 2) hardware failure 3) Local Service provider problem 4) LMI type inconsistency 5) KeepAlive not sent 6) package type inconsistency 7) DLCI inconsistent
From frame delay network cannot ping remote host 1) DLCI specified wrong interface 2) package type inconsistency 3) ACL problem 4) interface configuration error
2) Questions and actions
Problem-Solving Action programme
Cable fault 1) Check the cable and test the Connector 2) Replace the cable
Hardware failure 1) perform loop test to detach hardware 2) connect the cable to another interface of the same configuration as the router, such as OK, you need to replace the hardware
Local Service provider issue 1) such as loop test makes LMI state up, but cannot connect to the remote site, contact local carrier 2) contains carrier problems as if FR misconfiguration, such as DLCI inconsistency or encapsulation inconsistency.
LMI type inconsistency 1) Verify that the router's LMI type is consistent with each device on the PVC 2) If you use a public provider network, you cannot access LMI, contact the provider
KeepAlive question 1) Use show interface to see if keepalive is disabled, or verify that KeepAlive is configured correctly 2) if the keepalive is set incorrectly, enter configuration mode and specify the KeepAlive interval on the interface
Package Type 1) Verify that both routers are packaged in the same way, and if there are non-Cisco routers, the IETF must be used. Display package information with the show Frame-relay Command 2) Replace the package with the encapsulation Frame-relay IETF, and set the encapsulation of a PVC with the available Frame-relay map.
DLCI inconsistent 1) show running-config and show Frame-relay PVC display assigned to an interface DLCI number 2) If the DLCI number is configured properly, contact the vendor to verify that the FR switch is the same DLCI
ACL problem 1) parses ACLs using show IP interface display applied to ACL2 on the interface, deleting or modifying it if necessary
From for notes (Wiz)
The 7th chapter deals with serial line and Frame Relay connection failures
