Troubleshooting Inter-VLAN Routing

This topic is to discuss the following lesson:

Nice. you are awesome Rene. God bless you.
because of you, i have cleared my first round of interview. Interviewer asked me one question to which i haven’t answered well.
What are steps you will take to troubleshoot a network running ospf protocol?

Could you please help with this?

Hi Rohit,

Sorry for the late reply. In case anyone else reads this, I have two good documents of how to troubleshoot OSPF:

nice units so far. Only three more units to go until finish my first round of studying for Tshoot. I love learning and studying but sometimes when your really hard at it for a few days some of the fun is lost and it becomes work.

1 Like

Hi Renee thabnks very helpful

Hi Laz,

Is this possible to assign ip addresses of different n/w to vlans b/c here ports are switchport not routed. this dragged me in confusion regarding assignment of the ip addresses to the VLAN, kindly clarify.

Hello Pradyumna

You cannot assign IP addresses to switchports because they are Layer 2 ports, but you can assign VLANs to switchports. Each VLAN on a switch can have one or more switchports assigned to it. In addition, each VLAN must have a configured SVI in order for hosts on that VLAN to be able to access other networks. The SVI is configured with an IP address and acts as the default gateway for that subnet.

For this reason, IP addressing must correspond to the VLANs that exist on a switch. What this means is that a single VLAN will typically correspond to a single IP subnet, with a single SVI acting as the gateway for that subnet.

Within a single multipoint switch, you can only have a single SVI per VLAN, and thus only a single IP address for the default gateway. Now if you have two switches connected via a trunk, then you can have multiple SVIs with IP addresses. In this case, if you do use multiple SVIs on multiple switches for the same VLANs, you must be careful how you configure them. They should be on the same subnet, but you may run into some interesting behaviours such as unicast flooding and asymmetric routing. Take a look at this lesson for more information:

I hope this has been helpful!


Thanks for clarification Laz.I have one more doubt that is What is the SVI and why we need this, is SVI also used to put switch in VLAN as we want ?

Hello Pradyumna

An SVI is the same thing as a VLAN interface. It functions as a (virtual) routed port within the VLAN and acts as the default gateway for all hosts within that specific VLAN, when configured on an L3 switch. On an L2 switch, an SVI is simply an IP address you can use to connect to the switch itself using CLI with protocols such as SSH and telnet.

I hope this has been helpful!