Chapter 4 troubleshooting of TCP/IP Routing Protocol

1. Default Gateway
If the destination address of the package is not in the router routing table, if the router is configured with the default gateway, it will be forwarded to the default gateway; otherwise, it will be discarded.
Show IP route; view the default gateway of a Cisco Router

Ii. Static and Dynamic Routing

Iii. Handling k_protocal/04937.htm" target = "_ blank"> rip faults
Rip is the distance vector routing protocol, and the measured value is the number of hops. The maximum number of RIP hops is 15. If the number of hops to the target exceeds 15, it is not reachable.
Rip V1 is a classless routing protocol. Rip V2 is a non-classless routing protocol that supports CIDR, route induction, and vlsm. It uses multicast (224.0.0.9) to send route updates.
The show commands related to rip:
Show IP Route rip; only display rip route table
Show IP route; show all IP Route tables
Show IP interface; display IP interface configuration
Show running-config
Debug IP rip events;
Common rip faults: Rip versions are inconsistent, and rip uses UDP broadcast updates.

Iv. Handling IGRP faults
IGRP is a Cisco dedicated routing protocol, distance vector protocol. The IGRP metric value can be based on five factors: bandwidth, latency, load, reliability, MTU. By default, only bandwidth and latency are used.
Show commands related to IGRP:
Show IP Route IGRP; displays the IGRP route table
Debug ip igrp events;
Debug ip igrp transactions;
Common IGRP faults: access list, incorrect configuration, line down to the adjacent Router

V. Handling of VPN faults
It is a hybrid Link Status Protocol and distance vector protocol, and is a Cisco dedicated routing protocol. VPC uses the multicast address 224.0.0.10 to send route updates. The dual algorithm is used to calculate routes. The measured value of the network-VPN protocol is based on bandwidth, latency, load, reliability, and MTU. By default, only the bandwidth and latency are used.
VPC uses three types of databases: Route database, topology database, and adjacent router database.
Show commands related to the MongoDB:
Show running-config
Show IP Route
Show IP Route VPN; show only the OSPF route entries.
Show IP subnet interface; displays peer information of this interface
Show ip vpn nodes: displays all the nodes in the network and their information.
Show ip vpn topology; displays the content of the VPN topology table.
Show ip ospf traffic; displays the summary of the OSPF route statistics.
Show IP glasevents; displays the latest event records of the VPN protocol.
Debug commands related to the MongoDB:
Debug IP ()
Debug IP: fig
Debug IP subnet configurations
Debug IP: VPN gateway
Debug IP subnet
Common VPN faults: loss of neighboring relationships, default gateways, routes of old IOS versions, and stuck in active.
When dealing with a VPN failure, first view all the adjacent routers with show IP subnet gigrp, then use show IP Route gigrp to view the route table of the router, and then use show IP subnet topology to view the topology of the router, you can also view whether route updates are sent by the show IP address (OSPF) traffic.
6. Handling OSPF faults
OSPF is a link status protocol that maintains three databases: adjacent databases, topology databases, and route tables.
Show commands related to OSPF:
Show running-config
Show IP Route
Show IP Route OSPF; only display OSPF routes
Show ip ospf process-ID; displays information related to a specific process ID
Show ip ospf; displays OSPF Information
Show ip ospf border-routers; display VBR
Show ip ospf database; display OSPF inductive Database
Show ip ospf interface; displays OSPF information on the specified Interface
Show ip ospf neighbor; displays OSPF adjacent Information
Show ip ospf request-list; display the link status request list
Show ip ospf Summary-address; displays the republishing information of the inductive route.
Show ip ospf Virtual-links; displays virtual link information
Show IP interface; display the IP settings of the interface
Debug commands related to OSPF:
Debug ip ospf;
Debug ip ospf events
Debug ip ospf flood
Debug ip ospf lsa-generation
Debug ip ospf Packet
Debug ip ospf retransmission
Debug IP OSPF SPF
Debug ip ospf tree
Common OSPF faults: Each OSPF area cannot exceed 100 routers, and the entire network cannot exceed 700 routers. The wildcard mask is improperly configured;

VII. Handling BGP faults
The key configuration of BGP (including ibgp and ebgp) is the neighbor relationship, and BGP uses TCP to establish the adjacent relationship.
Show commands related to BGP:
Show ip bgp; displays the Routes learned by BGP
Show ip bgp network; displays the BGP information of a specific network
Show IP neighbors; displays BGP neighbor Information
Show ip bgp peer-group; displays BGP peer group information
Show ip bgp summary; displays the summary of all BGP connections
Show IP Route BGP; displays the BGP Route table
BGP-related debug commands:
Debug ip bgp 192.1.1.1 updates
Debug ip bgp dampening
Debug ip bgp events
Debug ip bgp keepalives
Debug ip bgp updates
Typical BGP faults:
8. re-release the Routing Protocol

IX. TCP/IP symptoms and causes
Symptom cause
The local host cannot communicate with the remote host. 1) DNS is not working properly. 2) No route to the remote host. 3) the default gateway is missing. 4) Management rejection (ACL)
An application cannot work normally. 1) management deny (ACL) 2) the network is not configured properly to process the application.
Startup failed 1) BOOTP server no MAC address entity 2) IP helper-address3 missing) acl4) Modify Nic or MAC address 5) Duplicate IP address 6) abnormal IP configuration
Remote Host cannot be pinged. 1) acl2) No route to the remote host. 3) No Default Gateway is set. 4) remote host down.
Route 1 missing) route protocol not correctly configured 2) Release List 3) passive interface 4) Route neighbor not advertised 5) Route Protocol version inconsistent 6) No neighbor relationship established
No adjacent relationship is established. 1) Incorrect Routing Protocol configuration. 2) Incorrect IP configuration. 3) No network or neighbor statement is configured. 4) the hello interval is inconsistent. 5) Inconsistent area ID.
High CPU utilization 1) unstable route updates 2) debug3 is not disabled) the process is too heavy
Active routing mode 1) Inconsistent intervals 2) Hardware problems 3) unstable links

10. TCP/IP symptoms and Action Plan
Problem Action Plan
DNS is not working properly. 1) configure the DNS host and the DNS server. You can use NSLookup to verify the DNS server.
No route to the remote host. 1) Use ipconfig/all to check the default gateway. 2) use show IP route to check whether the route is correct. 3) If no route is available, use show IP route to check whether there is a default gateway. 4) if a gateway exists, check the next hop of the target. If no gateway exists, correct the problem.
The issue of ACL separation is related to ACL. You must analyze the ACL, or override the ACL and apply it.
The network is not configured to process the application and view the router configuration
Booting failed 1) Check DHCP or BOOTP server, and check whether there is a Mac entity of the faulty machine 2) use debug ip udp to verify packets received from the host 3) Verify that helper-address is correctly configured 4) check whether the ACL has disabled the package.
Routing is missing. 1) Use show IP route on 1st routers to view the learned routes. 2) Verify the neighboring routers. 3) use the correct routing network and neighbor statement. 4) Use OSPF, verify the wildcard mask 5) Check the distribute list6 applied to the interface) Verify the IP Address Configuration of the neighbor. 7) if the route is published again, verify the measurement value. 8) Verify that the route is released normally.
No adjacent relationship is formed. 1) Use the show IP protocol neighbors list to view the adjacent relationship. 2) view the Protocol configuration that does not constitute the adjacent relationship. 3) Check the Network Statement in the route configuration. 4) use show IP protocol/interface to view specific interface information, such as Hello interval # Network Technology