Routing in switch

Posted on 2014-04-02
Medium Priority
Last Modified: 2014-04-10
I have server vlans in a switch and ip routing is enabled
when i do sh ip route it gives me one specific route is going from 1 vlan
but that Vlan has many interface , who can i find which interface the traffic is going from ?
specifically when we have many trunk links in that vlan.

Nitin Mohan
Question by:mohannitin
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LVL 57

Expert Comment

ID: 39972038
Do you understand how routing works?

Each IP host has a default route.  They may also have other routes for specific IP subnets.  Typically all hosts within the same subnet have the same routeing table.

Each IP host will look at its route table to see what router to forward traffic to.

Author Comment

ID: 39985556
if i am correct , the traffic from switch vlan would be forwarded from root port of that vlan.
as soon as it reaches the root switch will forward the traffic to specific subnet using routing table
LVL 57

Accepted Solution

giltjr earned 2000 total points
ID: 39986125
Not really.  When you are talking VLAN's and root port, that is layer 2, switching, not layer 3 routing.

For routing the sending host looks at its routing table to find out what IP route to take to send to the target host.

If the sending and target are on the same subnet, the sending host issues a ARP to find the target host's MAC address and then sends the packet within a layer 2 frame.  That is where the VLAN/layer 2 path comes into play.  You only have a "root path" if  you have multiple layer 2 connections between layer 2 devices and you are using spanning tree to prevent loops.

If the sending host and the target host are not in the same subnet, the sending host finds the IP address of the next hop, that is the router it should use to forward the packet to the target host.  The router and the sending host will be on the same subnet, so the sending host will send a ARP to the router to get its MAC address.  It then sends the packet to the MAC address of the router.  The router will then look at the target host's IP address and look at its routing table to see how to get to the target host.

Author Closing Comment

ID: 39991433
awesome answer , thanks for the clarification

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