enter image description here I was reading about how a packet is send from one host to another. I am confused about entries that will be made in layer-3 switch routing table. Does it contain the entries for layer two switches or does it contain the entries for all the hosts (A,B,C,D ... etc).


A routing table will have entries for the directly connected networks, any static routes you have configured, and any routes learned through routing protocols that you may be running to exchange routes with other routers.

The routing table entries for each network will include the interface to which traffic destined for that network should be sent.

Based on you drawing: You could have three routes for the directly connected networks. You probably have a statically configured default route for the Internet, or you may be running BGP with the ISP router to which your layer-3 switch connects, in which case, you may have other routes learned from the ISP router.

  • Thanks, for the reply. But i'm still confused about Layer-3 switch routing table. Layer-3 switch routing has details (Network id, netmask, next hop, Interface) for an entry. But layer two switch has no IP address. And Host A,B,C are in one subnet and hosts D,E,F,G are in other subnet. So i'm also confused about who is managing networks layer-2 switch or layer-3 switch.
    – Patt
    Nov 9 '16 at 18:36
  • Layer-2 switches are only concerned with layer-2, and they know nothing about layer-3 networks. A layer-3 switch is a layer-2 switch, but it has a routing module. Layer-3 and layer-2 really know nothing about the other. There are many layer-2 protocols which can each carry a variety of layer-3 protocols. The layer-2 protocol doesn't really care what layer-3 protocol it encapsulates, nor does the layer-3 protocol care in which layer-2 protocol it is carried. Layer-2 simply knows nothing about routes, it delivers frames based on the layer-2 address on a flat layer-2 network.
    – Ron Maupin
    Nov 9 '16 at 18:43

Layer2 won't understand ip address , layer2 switch will only forward traffic on basis of mac-addres table

Let have example

Packet forwarding to host A from layer3 switch

Once the packet reaches layer3 switch as host A as destination , layer3 devices process this packet by varyfying routing table , in routing table it found that this network was directly connected networks .hence packet is forwarded on interfàce where network is connected so in this case packet is forwarded to access-switch layer2 Switch1 from this switch frame is forwarded to correct destionation based on mac -address table present in Switch1.

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