difference between svi and vlan

[ilyas001]

hi guys i don't get the difference between this two concepts at all , i understand that i use svi to give a ip address to the switch n case i need to connect via ssh and also i understand that i need a vlan to make virtual lans all over my network , but still i feel very confused because a svi is the configuration of vlan1 then why even have svi in the first place  . also can anyone here tell me if i can use the same vlan in two different lans ?

[U.Ho]

vlan = virtual local area network

svi = switch virtual interface

 

Simply but not too accurately put: vlan is the network, svi is an interface in that network. As it is a virtual network, the interface is also virtual.

 

If you could elaborate a bit. What switch are you trying to configure? Cisco?

[U.Ho]

Oh, and what do you mean by same vlan in two different lans?

 

If you look at the question in a global scale, I'm sure there are vlan10 for example used in thousands and thousands of networks. 

[ilyas001]

1 minute ago, U.Ho said:

vlan = virtual local area network

svi = switch virtual interface

 

Simply but not too accurately put: vlan is the network, svi is an interface in that network. As it is a virtual network, the interface is also virtual.

 

If you could elaborate a bit. What switch are you trying to configure? Cisco?

i use packet tracer so it's only cisco stuff right now i try to understand svi and vlans in depth ,so if i get you just told me i use vlan 1 because by default it have all the interfaces of the switch in it so if i need a remote  control of the switch  i will be able to use ssh from all possible interfaces right ? for example if i sue a vlan 2 that only have fast 0/1 and 0/2 with a ip address so if i try to ssh the switch with that ip address from fast 0/3 i would not be possible , because fast 0/3 isn't a vlan's 2 svi ?  

[ilyas001]

4 minutes ago, U.Ho said:

Oh, and what do you mean by same vlan in two different lans?

 

If you look at the question in a global scale, I'm sure there are vlan10 for example used in thousands and thousands of networks. 

well for that i mean i watched a video that said that i could use vlans to make a virtual lan in two different subnets for exemple i have a 192.168.1.0 subnets and a 192.168.2.0 subnets i can use vlan to take 3 interfaces from 192.168.2.0 and add them to 192.168.1.0 i can give you a link to the video if you want 

[U.Ho]

7 minutes ago, ilyas001 said:

i use packet tracer so it's only cisco stuff right now i try to understand svi and vlans in depth ,so if i get you just told me i use vlan 1 because by default it have all the interfaces of the switch in it so if i need a remote  control of the switch  i will be able to use ssh from all possible interfaces right ? for example if i sue a vlan 2 that only have fast 0/1 and 0/2 with a ip address so if i try to ssh the switch with that ip address from fast 0/3 i would not be possible , because fast 0/3 isn't a vlan's 2 svi ?  

Ok I think you almost got it.

If you make an "interface vlan1" and give it an IP address you can ping the ip address from ports that are access ports for vlan 1 but not ports that are access ports for anything other than vlan1.

 

Now, a physical interface is not svi. When you issue the command "interface vlan1" you enter svi configuration mode for the vlan1 svi.

 

I think a better analogue for understanding svi is two switches connected with a trunk link that only allows let's say vlan 10. Then you have a svi for vlan2 on the other end and svi for vlan10 on the other end. Now, you should be able to see the vlan10 svi from the other switch but not the vlan2 svi from the other switch respectively.

 

Using vlan1 with trunks is risky if you're not yet familiar with the concept of native vlan. That's why vlans 2 and 10.

 

Let me try and tl;dr it: svi is the vlan interface, not to be confused with the physical interface.

 

14 minutes ago, ilyas001 said:

well for that i mean i watched a video that said that i could use vlans to make a virtual lan in two different subnets for exemple i have a 192.168.1.0 subnets and a 192.168.2.0 subnets i can use vlan to take 3 interfaces from 192.168.2.0 and add them to 192.168.1.0 i can give you a link to the video if you want 

Yea I'm not sure what you're trying to accomplish with this. Why not use a bigger subnet mask if you need more hosts than a given subnet can accommodate?

[ilyas001]

15 minutes ago, U.Ho said:

Ok I think you almost got it.

If you make an "interface vlan1" and give it an IP address you can ping the ip address from ports that are access ports for vlan 1 but not ports that are access ports for anything other than vlan1.

 

Now, a physical interface is not svi. When you issue the command "interface vlan1" you enter svi configuration mode for the vlan1 svi.

 

I think a better analogue for understanding svi is two switches connected with a trunk link that only allows let's say vlan 10. Then you have a svi for vlan2 on the other end and svi for vlan10 on the other end. Now, you should be able to see the vlan10 svi from the other switch but not the vlan2 svi from the other switch respectively.

 

Using vlan1 with trunks is risky if you're not yet familiar with the concept of native vlan. That's why vlans 2 and 10.

 

Let me try and tl;dr it: svi is the vlan interface, not to be confused with the physical interface.

 

Yea I'm not sure what you're trying to accomplish with this. Why not use a bigger subnet mask if you need more hosts than a given subnet can accommodate?

ok i get it , so in a vlan you will make a groupe of interfaces that you can use for remote control using a svi  that is the ip address of the vlan if i got it right this time . so svi is a part of vlan functionalities is there any other functionality i should know before ? also here is the video that i saw  maybe it will help you get my problem 

 

[U.Ho]

4 minutes ago, ilyas001 said:

ok i get it , so in a vlan you will make a groupe of interfaces that you can use for remote control using a svi  that is the ip address of the vlan if i got it right this time . so svi is a part of vlan functionalities is there any other functionality i should know before ? also here is the video that i saw  maybe it will help you get my problem 

 

Ok. I think I get it.

 

The video doesn't really mention SVIs at all nor is one needed to make things happen like in the video.

 

Notice there's a router that has connection to all the VLANs. That's the routing point and it does the routing via IP routing, not VLANs. In fact a router is not really conscious about vlans at all, but rather just subnets in this case.

 

Say the blue network is 192.168.1.0, red is 192.168.2.0 and green is 192.168.3.0, all with a subnet mask of 24 bits or 255.255.255.0. The networks can't switch packets as long as the router is not connected. When you connect the router and configure the blue, red and green interfaces with proper gateway addresses (interface IPs for the router), you can then route the traffic through the router.

 

If you do have a svi lets say in the blue network,  you can then with the router in place reach the svi from red and green networks as long as they're routed properly.

 

This is really more of routing than switches and vlans though.

[U.Ho]

Here's a video that explains this in more detail.

 

 

[ilyas001]

thanks bro i'm giving this a shot if i will let you know if i have any further question also i want to understand why od i need to have a default gateway address configured with my switch