Traffic flow in Flat layer 2 Network

[mahesh18]

Hi everyone,

Need to understand in flat layer network where we have core switch which is vtp server.

Then we have access switches they are also layer 2 and status is VTP client.

Then we have distribution switch which are also layer 2 and are VTP client.

Here access and distribution switches have same ip default gateway.

This gateway is for management access to switches only.

When i check on access switch it has all the vlans as its learning all the info from Core which is VTP server.

Need to undertsand how user traffic is routed to the core switch? as defualy gateway is only for management purposes?

Thanks

MAhesh

[Reza Sharifi · Accepted solution]

Hi Mahesh,

Need to undertsand how user traffic is routed to the core switch? as defualy gateway is only for management purposes?

From you description, user traffic is not routed to the core. it is switched using vlans with trunks between access, distro and core.

The management IP address on layer-2 devices is just to manage the equipment via telnet or SSH, so you can get to them remotely.  So, the only traffic that is routed is the management network not the users.

HTH

Reza

[mahesh18]

Hi Reza,

Thanks for reply back.

Here are more questions

So if access layer switch  have say 10 vlans   and all the traffic is passing through trunk links to core right?

Also core switch routes traffic to the destination where ever it need to go?

When i ping from my PC  to say some IP which is in different subnet from my PC then that ping is successfull.

so this ping request from my pc goes upto the core switch and core switch then passes that ping traffic to the right subnet?

Thanks

MAhesh

[Reza Sharifi · Accepted solution]

Hi Mahesh,

All correct.  So, if you have 10 vlans on your core router/switch configured with 10 SVIs for your users, you will also have another vlan vlan/svi for your management. And as you said if your PC is in managment subnet the traffic will go from your PC to the management vlan/svi, from there,  the core router/switch will route the traffic to what ever the destination vlan is. If your PC is in one of user subnets, the switch sends an ARP request for the MAC address of the default gateway of that subnet on the core switch and in this case the router will router from that subnet to another one since all the svis are directly connected to the core switch/router

HTH

Reza

[mahesh18]

Hi Reza,

This question was in my mind for quite sometime.

Now doubt has been cleared thanks to you.

Regards

MAhesh

[mahesh18]

Hi Reza,

To add litte more into this --

Core switch is VTP server

Distribution and access are layer 2 only and they are VTP client.

Now User is connected to Access layer switch say vlan 10.

The SVI  vlan is not in core switch1.

Its in Core switch 2.

Say This SVI vlan is connected to some other core switch

--------Core2-----------Core1-------Distribution-----Access----user  PC  ---Vlan 10.

Core2  has SVI  Vlan 192.168.10.1

User PC  gateway IP is 192.168.10.1

Now when user access any web traffic  the request goes to its Default Gateway of PC  which is  IP of SVI Vlan 10 via Core Switch 1 Right?

Regards

MAhesh