Routing

Expand all | Collapse all

Multiple IP subnets on the same interface

  • 1.  Multiple IP subnets on the same interface

     
    Posted 01-31-2021 08:39
    Hi everyone.

    Is there a use case for having more than one IP address (of different subnets) on the same L3 interface as shown below:
    set interfaces ge-0/0/0 unit 0 family inet address 10.10.1.0/24
    set interfaces ge-0/0/0 unit 0 family inet address 10.10.2.0/24

    Regards,
    Deepak


  • 2.  RE: Multiple IP subnets on the same interface

     
    Posted 01-31-2021 11:23
    You could do things like this (either with the same subnets (like in the diagram) or different subnets (like your example):
      

    Maybe the device in the middle does not support vlans (yeap, what are the changes of that? but you never know).

    Regards, 

    ------------------------------
    Yasmin Lara
    Juniper Ambassador
    JNCIE-SP, JNCIE-ENT, JNCIE-DC, JNCIE-SEC
    JNCDS-DC, JNCIA-DevOps, JNCIP-CLOUD, CCNP-ENT
    ------------------------------



  • 3.  RE: Multiple IP subnets on the same interface

     
    Posted 01-31-2021 12:09
    Thanks Lara.

    So the use case is to route using a single interface instead of two, correct?

    Thanks,
    Deepak.


  • 4.  RE: Multiple IP subnets on the same interface

     
    Posted 01-31-2021 22:05
    Yes, it is a way to go around certain situations so that you can route traffic a certain way.  Basically, you are creating two different networks over the same interfaces.  

    Going back to my example, you want to force the traffic through the SRX, but the two routers and the SRX are on the same VLAN. 

    Ideally,  you would just create a couple of vlans like this: 


    Which logically can be represented like this:


    But sometimes you are not under ideal circumstances,  for either technical or non technical reason.  One time, we had to do something like this in our office, because we didn't have the password to access the switch.... ;-)

    So, you just go around the limitation by doing this: 


    Also, having multiple IP addresses in the loopback interface is pretty common practice. The different addresses can be used for different applications/services, like BGP/L3VPNs, multicast,  tunnels, and so on, and the addresses can be selectively advertised in say ISIS/LDP/BGP... 


    Regards, 

    ------------------------------
    Yasmin Lara
    Juniper Ambassador
    JNCIE-SP, JNCIE-ENT, JNCIE-DC, JNCIE-SEC
    JNCDS-DC, JNCIA-DevOps, JNCIP-CLOUD, CCNP-ENT
    ------------------------------



  • 5.  RE: Multiple IP subnets on the same interface

     
    Posted 02-02-2021 01:04
    Thanks Lara!