I am confused in routing
I have 5 6500 switches (4 are core devices and 5th is used for WAN).It is collapsed core design.
Each core switch has a common 2 common vlans which are access ports (vlan31 and 25). ospf is used as RP with area 0 only
I have a 3750 (layer 2) switch hanging off core swich 4. A trunk connection is running between the two.
core switch 4 does not have vlan 20. it only has a route 192.168.20.1 (vlan20 ) thru switch 5 as vlan 20 sits on switch 5.
My question is if i create vlan 20 on 3750 switch and include in the trunk to core 4 (no vlan 20 on core 4) , will vlan 20 be routable thru switch core 4. core 4 only has a route to vlan 20 thru connected switch 5.
How can this be achieved.
I am sorry i couldnt understand the last sentence of your reply
It's just a simple routing concept as whenever a traffic comes for vlan 10 subnet to core 4 switch it needs to point towards the devices which has vlan 10 ip subnet that will SVI vlan 10 ip address of switch 3750.
Appreciate your help
What i means is switch 3750 having vlan 10 subnet connected hosts, so whenever a traffic hits in core 4 for vlan 10 subnet it needs to route the traffic to wards 3750 vlan 10 SVI ip address to have a complete routing connectivity for vlan 10 to others.
Hope to help !!
Why would i need an SVI on Core 4 or trunk to SWI 5 in order to perform intervlan routing as Core 4 already has a route to 220.127.116.11 network in its routing table
Okay, let me try and explain it a bit differently. I'm making the following assumptions -
1) that the 3750 that your host is connected to does not have an SVI for vlan 20 ?
2) that the 3750 is connected to core 4 via a trunk but is not connected to SW5
3) that you have created vlan 20 on core 4 (not an SVI) just the vlan
If that is correct the key to understanding this is that core 4 has a route to 192.168.20.0. So for core 4 to send any packets to that subnet it must route them ie. it cannot switch them at L2 it has to route them at L3.
So a host in vlan 20 sends a packet from the 3750. It is sent across the trunk to core 4. Now core 4 receives a packet in vlan 20. If the packet is already in vlan 20 then it can route the packet because by definition routing is moving packets between networks. So the fact that core 4 has a route to vlan 20 pointing to sw5 is useless in this case ie. you can't route within the same subnet.
So you can do one of the 3 things -
1) create an SVI for vlan 20 on core 4. Note that you then wouldn't need the route pointing to sw5 but you would need either
i) a connection between core 4 and SW5 that is in vlan 20
ii) a trunk link between core 4 and SW5 that allows vlan 20
2) create a trunk link from core 4 to SW5 which is the simplest way to get it to work.You also wouldn't need the route on core 4
3) create a new vlan eg. vlan 21, put the host on the 3750 into that, create the SVI for that new vlan on core 4 and leave the route in.
If you do 2 then the packet arrives at core 4 in vlan 20, is then forwarded onto the trunk link to SW5 still in vlan 20 and arrives at SW5.
If you do 3 then the packet arrives at core 4 in vlan 21 and can then be routed to SW5 using the route you have on core 4.
Thanks for the reply
4 core switches are connected thru 2 access ports on each switch ( vlan 31 and vlan 25)
SWI4 ------> SWI3 ------> SWI2 ------->SWI1
Basically the answer in my last post still stands ie. you will need vlan 20 on core 4 and in addition you either need to route vlan 20 core 4 or have a trunk link to switch 5.