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Therefore, at this point, the ARP and IP routing tables appear to be correct on Router 2.

In Example 4-8, the router is indeed reachable through ICMP.Įxample 4-8 proved that the next hop is reachable from both Router 2 and the host, 10.1.1.100. Therefore, you should understand your network policies when troubleshooting or installing systems. Some network routers' security policies can also prevent the routers from responding to very high rates of ICMP packets. These reasons include encoding errors in WAN circuits, fragmentation configuration issues, hardware issues, Virtual Private Network (VPN) misconfiguration, software features such as encryption and compression, and so on. You must verify various packet sizes because defaultsized packets of ICMP echoes can be routed and switched correctly in the network, whereas larger packets can be dropped for a multitude of reasons. The next step is to verify IP connectivity to the next-hop router, Router 1, from both the host, 10.1.1.100, and Router 2, as shown in Example 4-8.Įxample 4-8 Verifying IP Connectivity to the Next Hop from Router 2 and the Host, 10.1.1.100Įxample 4-8 also issued an ICMP ping of a larger packet size for continued verification of accessibility of the next-hop router. Therefore, at this point in troubleshooting, both the routing entry and ARP entry for the next-hop router are correct. The next-hop router's (Router 1's) MAC address is indeed 7c.

Example 4-7 illustrates obtaining Router 1's MAC address for the interface configured with the IP address 172.18.114.1.Įxample 4-7 Verifying the MAC Address of an Interface in Cisco IOS This step verifies that the correct ARP entry exists for the next-hop router. This is the gateway of last resort.Įxample 4-6 Verifying IP Routing Table and Next-Hop InformationĪlthough the ping from the router was successful, the next step is to verify the MAC (Hardware Addr) of the next-hop router.

The host entry, 10.18.118.184, is known through a static route with a metric of 0 according to the show ip route command. Example 4-6 also confirms the route to the host, 10.18.118.184, and verifies the ARP entry for the next hop for 10.18.118.184, which is 10.18.114.1. The first step in troubleshooting is to access the first-hop router, Router 2, and verify IP connectivity to the SFTP server, 10.18.118.184. Figure 4-3 Troubleshooting IP Connectivity and Verifying the IP Routing TableĮxample 4-5 IP Connectivity Issue from the Host, 10.1.1.100, to the Target, 172.18.118.184, Based on Figure 4-3