In that case, I need to find out if the remote router is attached, up and running. If not, the IP communication principially cannot work, so I do not even try using IP-based troubleshooting tools. Usually, when I cannot ping the other end router, I at least have a look into the ARP table whether the remote router's MAC address has been discovered via ARP. To populate an ARP table, you absolutely need to have an ARP conversation with the other router, and if the other router does not respond to ARP, there is no way of you learning its IP/MAC mapping automatically. Neither the routing table nor the ARP table is populated based solely on an IP packet received from the other end. On a routed interface, your options are extremely limited.
#Cisco mac address table 消去 how to
How to troubleshoot in Layer 2 perspective if the Remote end router is not reachable? That is the impulse for your router to send the packet out gi0/1, populating the ARP table in the process. That is because when you ping the other end, you ping a host that is in the same IP network as your gi0/1 interface. The same process would happen if the destination was reachable via an IP next hop address that belongs to the IP subnet of gi0/1 - that next hop address would be looked up in the ARP table, and if it is not there, the router would need to send an ARP request.īut I am able to ping the Remote end Router connected to GE0/1, though there is no MAC address entry in the MAC address table (of course the MAC address of the remote router is in the ARP table) If it isn't, it will broadcast an ARP request and wait for the reply. When your router needs to send a packet to someone else in the same subnet, it will first do a lookup in the ARP table to see if the IP/MAC mapping is already there. Keep in mind that our gi0/1 interface is assigned an IP address in some IP subnet. If the routing table does not point out the gi0/1 interface, no packets are going to be sent out that interface.
Then, and only then, the router will try to forward the packet out the gi0/1 interface. The routing table is the key answer here - it is exactly the routing table that will say: "With this packet, you need to send it out the gi0/1 interface". That means that whatever is going to be sent out that interface is primarily determined by routing, not by switching.
The gi0/1 interface on your router is a routed interface. I thought the router will learn the MAC Address of the remote end router and populate that in the MAC address table. With that said, if I have a Metro Ethernet Link connected to one of the GE Routed Port (GE0/1), how does the router reaches the other end peer router. On a router without a switching module, this command displays nothing. If there was a switching module installed into the router, the show mac address-table would show you the MAC addresses learned on individual ports of the switching module.
This command would display a non-empty output if your router had a switching module installed, such as HWIC-4ESW or similar, because in that case, the router also has a switching hardware and behaves both as a router and as a switch. On a router, you may find that the show mac address-table command is supported. Note that MAC address table and ARP table have nothing in common, and you do not need to maintain one to populate the other. ARP table maps IP addresses of directly attached neighbors to their MAC addresses. MAC address table maps MAC addresses to switchports where the owners of individual MAC addresses are attached. Please do not confuse MAC address table and an ARP table. Routers do not normally maintain MAC address tables.
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