Catalyst 2-Layer Exchange 3-layer communication profile

This article discusses the issue of the second IP communication between the core switch and the converged switch interface.

When the core switch is configured with a second IP, the converged switch is connected to the core switch via trunk, and the configured interface IP and the second IP network segment can communicate normally when the pooled switch does not enable the 3-tier routing function, but when the converged switch enables the 3-tier routing function, The core switch does not access the converged switch.

To verify the phenomenon, two routing simulators were used, in the same way as iOS. found that the simulation of the convergence of routers, using IP default-gateway instead of IP route 0.0.0.0 0.0.0.0, the simulation of the core of the router can not ping the convergence, the use of the specified source ping, or the convergence can ping through the core, If you use IP route 0.0.0.0 0.0.0.0 you can. By grasping the bag found that the core router ping over the package, is some, but no answer packet, turn on debug IP ICMP, found that the convergence router is answered, but the interface does not send the packet, replaced by IP route 0.0.0.0 0.0.0.0 sent out. Seems to disagree with forum posts. IP route 0.0.0.0 0.0.0.0 is enabled routing, IP Default-gateway is not enabled, but after all, routers and switches from the mechanism is still different. In accordance with the requirements of the 3560G and 2960S, of course, the 2-tier 2,960 can only be equipped with IP Default-gateway, it is true that you can fully communicate, without any problems, it seems that the switch and router mechanism is really different. The communication of the switch is the cam table, not the routing table. Open 2960 ip arp, found just and switch communication is not and switch IP a network segment address, also unexpectedly all impressively in the column, really embodies the 2 layer exchange, communication is not by IP route, the direct IP address is the MAC address, not a network segment is also the case, So the 2-layer switch can be in the 2-layer state, to 2-layer MAC address to communicate, and the IP routing after the introduction, according to the 3-tier routing rules, but not.

The point of view of the problem should be that the convergence switch has routing enabled and may not use the IP route 0.0.0.0 0.0.0.0 command.

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