update-packets
Content 5.3 Common IGP Routing Protocol Issues, Causes, and Solutions 5.3.7 Passive interface The passive-interface command works differently with the different IP routing protocols that support it. RIP/IGRP – With RIP and IGRP, routing updates are received, but are not sent. EIGRP – With EIGRP, the router stops sending hello packets on passive interfaces. When this happens, EIGRP cannot form neighbor adjacencies on the interface, and routing updates can neither be sent nor received. OSPF – With OSPF, routing information is neither sent nor received on a passive interface.The network address of the passive interface appears as a stub network in the OSPF domain. This example shows two routers running IGRP between each other. When an interface is defined as passive under IGRP, IGRP will receive updates on that interface but will not send any updates. The passive-interface command is used to avoid sending unnecessary updates to a neighbor that does not need to receive any IGRP updates, such as a small router at the edge. A simple default route is enough information for that router to talk to the outside world. It is important to use the passive-interface command only where needed. If not, undesired results might occur. Debugs and Verification
Figure shows the output of the show ip protocols command, which shows the outgoing interface is defined as passive. Figure shows the configuration of router R1, which shows that the outgoing interface is defined as passive. Solution
Figures and confirm that the interface Ethernet 0 is defined as passive, so router R1 is not sending any updates on Ethernet 0. Sometimes, it is desirable for some networks to be advertised and others to be filtered. In this situation, a distribute-list out would be a better solution. In this example, the assumption is that the passive-interface was configured by mistake, and this command needs to be removed to solve this problem. Figure shows the new configuration to solve this problem. Figure shows the routing table entry on router R2 after fixing the problem. Commands used in this example and some of the commands that can be used for other routing protocols include:
Content 5.4 Troubleshooting RIP 5.4.1 Incompatible RIP version types When RIP is configured on a router, by default, the software receives RIP Version 1 (RIP v1) and RIP Version 2 (RIP v2) packets, but sends only RIP v1 packets. To send and receive only RIP v1 packets, the router must be configured with the command version 1 under router rip. To send and receive only RIP v2 packets, the router must be configured with the command version 2 under router rip. When the version command is used, by default, updates from other routers sending other than the specified version are ignored. This example shows two routers running RIP between each other. Debugs and Verification
Figure shows the configuration of router R2. In this configuration, RIP is configured to send and receive only Version 1 packets. The default RIP configuration, without the version 1 command, will allow the router to receive both Version 1 and 2 packets. Figure shows the output of the debug ip rip command. This command reveals that router R2 is receiving a RIP packet from router R1, which is configured to send Version 2 updates. Figure shows the output of the show ip protocols command, which indicates that the Ethernet 0 interface is sending and receiving RIP v1 packets. This means that if a Version 2 packet is received on Ethernet 0 of R2, it will be ignored because the interface can send and receive only Version 1 packets. Figure shows the configuration of router R1. This shows that the sender R1 is configured to only send and receive Version 2 packets. Figure shows the output of the show ip protocols command, which shows that sender R1 is sending and receiving only Version 2 packets. This is because of the version 2 command that is configured under router RIP. Solution
An obvious solution is to configure all routers to run RIP v2. However, there may be times when this is not possible, and some routers can only run RIP v1. Therefore, another solution is to configure the appropriate interfaces to send and receive the appropriate RIP v1 or RIP v2 packets. If the receiver, R2, is configured to receive only RIP v1 packets, it will ignore the RIP v2 updates. Router R1 must be configured on the sender side so that it will send both Version 1 and Version 2 packets. When R2 receives the Version 1 packet, it will install the routes in the routing table. R2 will ignore RIP v2 packets because it is configured for RIP v1. Figure shows the new configuration for R1. In this configuration the sender, the R1 Ethernet 0 interface, is configured to send and receive both RIP v1 and RIP v2 packets. Figure shows the output of show ip protocols, which indicates that the Ethernet 0 interface is sending and receiving Version 1 and Version 2 packets. The advantage to sending both Version 1 and Version 2 updates is that, if any devices on this Ethernet segment are running Version 1 only or Version 2 only, those devices will be capable of communicating with router R1 on this Ethernet segment. Figure shows router R2 routing table after the configuration change.
Content 5.4 Troubleshooting RIP 5.4.2 Mismatched authentication key One of the options in RIP v2 is that RIP v2 updates can be authenticated for increased security. When authentication is used, a password must be configured on both sides. This password is called the authentication key. If this key does not match the key on the other side, the RIP v2 updates will be ignored on both sides. This example shows two routers running RIP between each other. Debugs and Verification
Figure shows the configurations of routers R1 and R2. In this configuration, a different RIP authentication key is configured on R1 and R2. The R2 Ethernet interface is configured with the key cisco1, whereas R1 is configured with the key cisco. These two keys do not match, so they ignore each other’s updates, and the routes will not be installed in the routing table. Figure shows the output from the debug ip rip command on router R2 that indicates that R2 is receiving a RIP packet that has invalid authentication. This means that the authentication key between sender and receiver does not match. Solution
When using authentication in RIP, make sure that the sender and receiver are configured with the same authentication key. Sometimes, adding a space at the end of the key can cause the invalid authentication problems because a space will be taken as a literal key entry. As a result, this causes a problem that cannot be corrected just by looking at the configurations. Debugs will show that there is a problem with the authentication key. To solve this problem, configure the same keys on both sender and receiver, or retype the authentication key, making sure that no space is being added at the end. Figure shows the new configuration to correct this problem. The authentication key is reconfigured on router R2 to match the key on router R1. Figure shows the routing table of R2 after the configuration change.
Content 5.4 Troubleshooting RIP 5.4.3 Reaches RIP hop count limit The RIP metric maximum is 15 hops. If a network has more than 15 hops, RIP is not a suitable protocol. Figure shows a network that produces a RIP hop-count limit problem. Router R2 is receiving an update for a RIP route, which is more than 15 hops away. R2 does not install that route in the routing table, as demonstrated in the