SVI and Routing HELP

[aleksandarsofranic]

When a vlan is forwarded to its default gatway(SVI) must that chassie have a routing table if it wants to route outside the lan? How does this process work? Lets say a member from vlan 10 wants to communicate to google, its not going to use inter-vlan routing with other SVI it must find a route outside right? How does this work? 

[Charles Hill]

AS long as your switch is a layer 3 switch,
-> create your svi's with an ip address and a ip helper address
-> Add a default route on your layer 3 switch, ip route 0.0.0.0 0.0.0.0 10.1.1.1
-> Pc's will send their internet traffic to the svi/their default gateway.
-> SVI/switch receives the request and forwards the traffic to the default route, 10.1.1.1
-> A routing protocol is not needed, only a default route.

If there is a problem with my logic, please correct me.  I'm learning something new every day.

[aleksandarsofranic]

With default route it should seem ok, but i am talking about bigger network solution with BGP-IGP routes, I presume that the L3 switch must have all routes localy of the network to route correctly..

Ip helper address is used when you must relay you dhcp messages/ broadcasts to the DHCP-server on a different subnet. This is not mandatory for routing

Please correct me if i am wrong i am learning too... thanks for the quick reply :D

[Adam White]

Hi, 

I am not really sure I understand your question. 

Your switch can have as many or little routes as required. 

When traffic arrives in a Vlan destined to the SVI on the switch for that vlan the switch will then look at its global routing table and find the best match. whether the routing table is 2 routes or 500, the process will be the same. 

The important part here is the traffic is DESTINED to the SVI of the switch. Otherwise it will just switch the packets and traffic remains in the VLAN. 

Does this answer your question.