Junos OS

Hi All,

This question has puzzled me for quite a while now, and I hope one of you can help me.

On Junos, to do inter vlan routing, it seems there are at least two ways of doing it.

1. using RVI - routed vlan interfaces.

http://kb.juniper.net/InfoCenter/index?page=content&id=KB11000

2. using sub-interfaces:

http://kb.juniper.net/InfoCenter/index?page=content&id=KB19477&actp=search&viewlocale=en_US&searchid=1422621966460

What's the difference between them, i.e. what's the benefit or limitations using one against another?

Thanks,

There are no differences in terms of actual of routing.  They both move packets from ingress interface A to egress interface B.

RVI must be used if you want multiple ports to be in the same VLAN and share the same layer 3 gateway (the same broadcast domain).  Sub-interfaces can be used when the layer 3 configuration is significant only to that specific port.  For instance, if you have 10 users on 10 separate ports and you want their IP default gateway to be 192.168.1.1, you need to configure an RVI.  If you have a single device attached to a port, such as an upstream router, a point-to-point circuit, or even a VM host with a VLAN trunk, you can use sub-interfaces (or just a single logical unit) if you want.

The other difference is that VLANs have local significance on sub-interfaces, and VLANs configured in the 'vlans' hierarchy have global significance.  This means you can have, for example, VLAN ID 100 configured as sub-interfaces on all 24 ports of an EX or QFX switch and they would all be separate, individual broadcast domains.  VLANs configured within the 'vlans' hierarchy have global significance, which means that 'vlan vlan100' is a single broadcast domain switch-wide.  You 'can' configure VLAN 100 as a global VLAN and VLAN 100 as a port VLAN, but they would be separate broadcast domains.

Make sense?

Thank you very much evt - yes it does make sense.

Hi,

They are few things are diffrent between RVI 's & Sub-Interfaces.

As I know in Routed Vlan Interfaces configuration we can add multiple layer2 interfaces to single RVI interface. And atleast  one physical interface should be up. iple l2 interfaces we can bind to 

Multiple L2 interfaces we can add to RVI's. But we can give only single IP address to subinterface.

And also single gateway for many host in RVI But subinterface is divinding the single physical interface into multiple L3 logical interfaces good for between two L3 devices.

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@M Suresh Reddy wrote:

Multiple L2 interfaces we can add to RVI's. But we can give only single IP address to subinterface.

 

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Perhaps this is not what you meant, but it is possible to add more than a single IP address to a sub-interface.

Hi evt,

Yes you are right!.

And here i am going to tell is the  IP you given to RVI as work as a gateway for many interfaces in downstream l2 interfaces. But subinterfaces is diffrent. 

As u told we can create multiple subinterface with many vlan_ID tags but logically its a L3 interface between two devices using single physical interface.

Yes, that is exactly what I said:

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@evt wrote:

If you have a single device attached to a port, such as an upstream router, a point-to-point circuit, or even a VM host with a VLAN trunk, you can use sub-interfaces

 

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