L2/3 switch intervlan behaviour

[Halil.Zakaria]

hello what happens in case of a L3 Switch that is capable of routing packets(in presence of a route entry)from an access-port(blongs to Vlan40) to a trunkport(allowed vlan 90).are we allowed to route this packet, if yes, will it keep its vlan tag 40?

[Ganesh Hariharan · Accepted solution]

i love your explanation, but with all that said, In distant site, is all my routed trafic into vlan 99 going to change its vlan tagging to vlan 99 ?

Hello Halil,

Ok ..Now got that what is your query is ..:)

Let me try to explain. Taking your example of Access Port VLAN 40 and trunk vlan 99 between switches.

PC1 ---(Vlan 40 Access VLAN)-- SWA -----(Trunk 99) --- SWB --- (VLAN 99) --Access Port of Firewall.

When packet leaves from PC NIC it lands on SWA ( Access Port over VLAN 40 ) which is untagged and you know that switch maintains Forwarding DataBase which comprised of tuples of three elements: (MAC, port, VLAN).

So it has full detail of vlan 40 PC1 mac address and port it is connected with vlan id in FDB of SW1.

So , In order to reach subnet behind vlan 99 traffic lands on VLAN 40 gateway which would SVI configured on SW1 and there happens inter vlan routing to VLAN 99 for destination subnet as per routing configured.

Once it lands on trunk port which encapusalted with 802.1q trunk which means vlan tagging is happening with VLAN 99 and packet reaches at SW B with destination and src ip.

Once Frame lands on SWB over the trunk with tagged , SW B checks FDB based on MAC which is been identify on packet destination ip. Which would be firewall interface on access port vlan 99 and packet goes to firewall interface untagged.

I Hope the above explanation would be helpful.

-GI

[Halil.Zakaria]

You cleared my doubts, Thnak you for helping