A Symptoms
If it is determined that there is no problem with the physical layer and the data link layer after the failure, then the conclusion that the problem lies in the network layer or the high-level layer can be drawn:
. All components on the network layer of the problem link do not work properly;
. The network can run but the performance (speed, response or throughput) is lower than that in the baseline state;
. There is no connectivity above the link transport layer;
. The PING command will occasionally succeed;
The routing table is empty, inconsistent or incomplete;
. Routing behavior is not expected;
. The grouping is forwarded to the wrong place;
. Different console messages reported failures and problems;
. The system's log files reported failures and problems;
. The network management system alarm prompts problems and failures.
Optimization problems may occur when the network can run and run at a level below the baseline at intervals. In this case, users report that data transmission is slower than usual, intermittent or inconsistent. Common evidence of the network layer indicates that not all network layer problems will have the same evidence. These symptoms can display the wrong routing forwarding of console messages to packets from the system (connectivity issues). 2. Commands and programs of terminal systems that isolate network layer problems.
Under WIN
. ping
. arp -a
. ipconfig[/all]
. tracert
. winipcfg
Under unix
. ifconfig -a
. traceroute
. route -n
cisco IOS commands
Used to isolate address resolution
. show ip arp
. debug arp
Isolate BGP problems
. show ip bgp --Show content of the current BGP table
. show ip bgp summary --Show list and status of all BGP connections
. show ip bgp neighbors -- Show information about TCP and BGP connections to neighbors
. show ip bgp flap-statistics -- display information about BGP routing fluctuations
. debug ip bgp[dampening|events|keepalloves|updates] -- Display BGP process information, other isolated IP communication and access list problem commands
. show ip traffic -- displays statistics of all IP traffic, such as: format error, bad hop count, encapsulation failure, unknown routing and detection proxy requests
. debug ip icmp --Show ICMP information
debug ip packet -- Display regular IP debugging information and IP security options (IPSO) security transactions
. show ip access-list[access-list[number|access-list-name]
Isolation problem at the network layer
Follow:
. Clarify the problematic sending and receiving devices;
. Ping network equipment along the way;
. Jump-by-hop test connectivity;
. Perform failures in both directions of the IP path;
. Use network topology diagram.
Four: Correcting the problem
1. cisco IOS commands
(1) Interface
. [no]ip domain-lookup
. interface [interface-type number]
. ip address ip-address mask [secondary]
. [no] ip redirects
- Example: If the multipoint connection of frame relay is established on the same subnet, it may be necessary to turn off IP redirection on the central device.
. bandwidth kilobits
--Specifying bandwidth value is for the load and utilization of the computer interface. Some routing protocols such as OSPF and EIGRP use this value to computer routing metrics (passing the bandwidth value of the interface to the upper layer protocol)
[no]ip proxy-arp -PARP is missing to enable. The router will respond to ARP requests, not only to its own IP address, but as long as this address can be reached through other interfaces. If the router's IP interface is connected to a network segment of an IP host that responds to PARP requests, use this command, that is, the default configuration of the IP interface of the CISCO router, it is very critical for these IP hosts to communicate with external devices on the subnet.
. ip helper-address address
- Make the interface monitor UDP broadcasts (often DHCP, NTP, TACACS, etc.) and send this request to the specified address server in the form of IP unicast. Because the client request sends broadcasts, they cannot reach different network segments. The helper-address command ensures that the client request is sent to the specified address and that the server's response can be sent to the network segment where the client is located. When the router sends the client request to the server, it actually specifies the network address from which the request originates. Based on this information, the DHCP server knows which address segment to select the IP address lease and assigns it to the requesting client.
[no]ip mroute-cache -Enable IP multicast fast or distributed switching (no disable)
(2) Access list
. access-list {access-list-number}
. ip access-group {access-list-number | access-list} [in|out]
(3) IP routing
. ip route prefix mask address [distance]
. ip route 0.0.0.0 0.0.0.0 {ip-address | interface-type number}[distance]
. ip route-cache
. ip split-borizon
---Applied in the distance vector protocol (IGRP and RIP), this command may be used when the center point connects two or more edge sites through multi-point connections (such as frame relay).
[no]passive-interface {interface-type number} -No update message is sent on a specific interface
. network
2. Terminal system commands
. arp -d -Delete entry from the ARP table
. route add
. ipconfig
. winipcfg
. ifconfig
5. Steps to correct network layer problems
Step 1 Make sure to save the current configuration of the device before changing the configuration of the device
Step 2 Make initial configuration changes
Step 3: Evaluate and archive changes and results
Step 4: Confirm that the changes have just solved the problem without introducing new problems
Step 5: Continue to make changes until the problem is solved
Step 6 If necessary, please seek help from external resources
Step 7 After solving the problem, archive the solution. Article entry: csh Editor in charge: csh
If it is determined that there is no problem with the physical layer and the data link layer after the failure, then the conclusion that the problem lies in the network layer or the high-level layer can be drawn:
. All components on the network layer of the problem link do not work properly;
. The network can run but the performance (speed, response or throughput) is lower than that in the baseline state;
. There is no connectivity above the link transport layer;
. The PING command will occasionally succeed;
The routing table is empty, inconsistent or incomplete;
. Routing behavior is not expected;
. The grouping is forwarded to the wrong place;
. Different console messages reported failures and problems;
. The system's log files reported failures and problems;
. The network management system alarm prompts problems and failures.
Optimization problems may occur when the network can run and run at a level below the baseline at intervals. In this case, users report that data transmission is slower than usual, intermittent or inconsistent. Common evidence of the network layer indicates that not all network layer problems will have the same evidence. These symptoms can display the wrong routing forwarding of console messages to packets from the system (connectivity issues). 2. Commands and programs of terminal systems that isolate network layer problems.
Under WIN
. ping
. arp -a
. ipconfig[/all]
. tracert
. winipcfg
Under unix
. ifconfig -a
. traceroute
. route -n
cisco IOS commands
Used to isolate address resolution
. show ip arp
. debug arp
Isolate BGP problems
. show ip bgp --Show content of the current BGP table
. show ip bgp summary --Show list and status of all BGP connections
. show ip bgp neighbors -- Show information about TCP and BGP connections to neighbors
. show ip bgp flap-statistics -- display information about BGP routing fluctuations
. debug ip bgp[dampening|events|keepalloves|updates] -- Display BGP process information, other isolated IP communication and access list problem commands
. show ip traffic -- displays statistics of all IP traffic, such as: format error, bad hop count, encapsulation failure, unknown routing and detection proxy requests
. debug ip icmp --Show ICMP information
debug ip packet -- Display regular IP debugging information and IP security options (IPSO) security transactions
. show ip access-list[access-list[number|access-list-name]
Isolation problem at the network layer
Follow:
. Clarify the problematic sending and receiving devices;
. Ping network equipment along the way;
. Jump-by-hop test connectivity;
. Perform failures in both directions of the IP path;
. Use network topology diagram.
Four: Correcting the problem
1. cisco IOS commands
(1) Interface
. [no]ip domain-lookup
. interface [interface-type number]
. ip address ip-address mask [secondary]
. [no] ip redirects
- Example: If the multipoint connection of frame relay is established on the same subnet, it may be necessary to turn off IP redirection on the central device.
. bandwidth kilobits
--Specifying bandwidth value is for the load and utilization of the computer interface. Some routing protocols such as OSPF and EIGRP use this value to computer routing metrics (passing the bandwidth value of the interface to the upper layer protocol)
[no]ip proxy-arp -PARP is missing to enable. The router will respond to ARP requests, not only to its own IP address, but as long as this address can be reached through other interfaces. If the router's IP interface is connected to a network segment of an IP host that responds to PARP requests, use this command, that is, the default configuration of the IP interface of the CISCO router, it is very critical for these IP hosts to communicate with external devices on the subnet.
. ip helper-address address
- Make the interface monitor UDP broadcasts (often DHCP, NTP, TACACS, etc.) and send this request to the specified address server in the form of IP unicast. Because the client request sends broadcasts, they cannot reach different network segments. The helper-address command ensures that the client request is sent to the specified address and that the server's response can be sent to the network segment where the client is located. When the router sends the client request to the server, it actually specifies the network address from which the request originates. Based on this information, the DHCP server knows which address segment to select the IP address lease and assigns it to the requesting client.
[no]ip mroute-cache -Enable IP multicast fast or distributed switching (no disable)
(2) Access list
. access-list {access-list-number}
. ip access-group {access-list-number | access-list} [in|out]
(3) IP routing
. ip route prefix mask address [distance]
. ip route 0.0.0.0 0.0.0.0 {ip-address | interface-type number}[distance]
. ip route-cache
. ip split-borizon
---Applied in the distance vector protocol (IGRP and RIP), this command may be used when the center point connects two or more edge sites through multi-point connections (such as frame relay).
[no]passive-interface {interface-type number} -No update message is sent on a specific interface
. network
2. Terminal system commands
. arp -d -Delete entry from the ARP table
. route add
. ipconfig
. winipcfg
. ifconfig
5. Steps to correct network layer problems
Step 1 Make sure to save the current configuration of the device before changing the configuration of the device
Step 2 Make initial configuration changes
Step 3: Evaluate and archive changes and results
Step 4: Confirm that the changes have just solved the problem without introducing new problems
Step 5: Continue to make changes until the problem is solved
Step 6 If necessary, please seek help from external resources
Step 7 After solving the problem, archive the solution. Article entry: csh Editor in charge: csh