08-15-2014 04:25 AM - edited 03-07-2019 08:24 PM
I have a question on how packets move between machines in the following scenario:
Switch A has IP routing enabled and has two vlans defined with an ip address assigned to each. Lets say those vlans are 10
and 20.
Switch B is trunked to switch A. On switch B I have two servers: one on vlan 10, one on vlan 20. Their gateway is
set to the IP address of their vlan on Switch A.
What I want to know is when I transfer stuff between the two servers on switch B, do all packets have to travel
through switch A? Do the packets stay within switch B? Do only the first few packets go to switch A to get routed
and then the rest stay within switch B?
If in case it matters, we're talking about TCP and UDP packets, maybe even some multicast traffic.
Thanks
08-15-2014 04:45 AM
Since you are transfering between 2 servers that are connected to switch B and the 2 servers are in the same vlan, the traffic never gets to switch A.
It is all local to switch B.
HTH
08-15-2014 05:10 AM
The two servers are not in the same vlan. One is on vlan 10, the other on vlan 20. Their gateway is the IP address set on their respectively vlans on switch A.
Thanks
08-15-2014 05:54 AM
In that case, the copmunication betweem the vlans will always go through their default gateways which is switch A.
HTH
08-15-2014 09:47 AM
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Posting
Normally, it's as Reza describes in his 2nd post. However, back in days of yore, the Catalyst 5000/5500 series supported multilayer switching with an external router. When active, the first packet would go to the router, and it would route it between the subnets/VLANs, but the switch would then note what it did, and for subsequent packets of the same flow, L3 switch locally between the VLANs.
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