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Layer 2 broadcast domain over layer 3 routed links

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  • 1.  Layer 2 broadcast domain over layer 3 routed links

    Posted 08-15-2018 15:20

    Hello all...

     

    I've been tasked with getting some paging equipment working on our campus network. Appears I need to have these touch screen stations in the same broadcast domain as the controller device....but reside in different buildings\routers.

     

    Our network is very tradidtional. Each building is fiber cabled to the campus core witch via their building core, which handles the routed links. Access switches (L2) are trunked off the buidling cores.

     

    What's the best way to span a layer 2 broadcast domain over a layer 3 routed uplink?? GRE??.......I don't care about encrpytion....just want said devices to live in the same l2 vlan across the routers.

    Also, there's no way to make an existing routed interface a 802.1q trunk as well correct? And only pass say a single vlan tag?

     

     Appreciate any help!! Thanks...Dennis

     

    EX series switches - 3300 4300 4600

     

     


    #vlan
    #layer3
    #GRE
    #broadcast
    #trunk
    #Layer2
    #domain
    #routedlinks


  • 2.  RE: Layer 2 broadcast domain over layer 3 routed links

     
    Posted 08-15-2018 21:16

    On both your core and access switches you can reconfigure your layer 3 uplink as a trunk port, and move your IP address to a new RVI. Then assign this vlan as well as the vlan you need to span to this trunk port. 



  • 3.  RE: Layer 2 broadcast domain over layer 3 routed links

    Posted 08-17-2018 06:37

    Thanks for the response. Understood, I wanted to keep the existing vlans and routing in tact though.....making the network L2 for all vlans across the buildings would mean readdressing everthing...having far reaching consequences. I was hoping that somehow I can have my layer 3 in tact, routing the vlans as we do now, with routed lings to the core....but then seletivly trunk\L2\bridge over the one vlan that I need to span the routed links...if that makes sense. 



  • 4.  RE: Layer 2 broadcast domain over layer 3 routed links
    Best Answer

     
    Posted 08-17-2018 07:37

    @dtopojr wrote:

    I was hoping that somehow I can have my layer 3 in tact, routing the vlans as we do now, with routed lings to the core....but then seletivly trunk\L2\bridge over the one vlan that I need to span the routed links...if that makes sense. 


     

    That's exactly what I'm describing.

     

    Before:

    L3 uplinks to edge A and edge B.

    All edge A subnets route through core via 10.0.0.0/30.

    All edge B subnets route through core via 10.0.0.4/30.

     before.jpg

     

    After:

    L2 uplinks to edge A and edge B

    All edge A subnets continue to route through core via irb.998 10.0.0.0/30.

    All edge B subnets continue to route through core via irb.999 10.0.0.4/30

    Vlan 10 spans the core from edge A to edge B.

     after.jpg



  • 5.  RE: Layer 2 broadcast domain over layer 3 routed links

    Posted 08-20-2018 07:19

    Ok...got you!! That's perfect....I labbed this in GNS3 (cisco images) and does what I need it to. Thanks for putting me on the correct path here!

    Much appreciated...

     

    Dennis



  • 6.  RE: Layer 2 broadcast domain over layer 3 routed links

    Posted 08-21-2018 14:46

    Smiker..... one last question if I may. i just made the mods on one site tonight on my prod juniper network.

    As fate would have it ..... I lose my rip neighborships when I config the uplinks in that way. Making them L2 trunks as opposed to routed interfaces -create a vlan for the uplink network - in this case 10.1.1.16/30 - and attempt to route via the irbs\vlan interfaces (ex3300). Is there a limitation using rip in this way?

     

    I can ping between the 2 10.1.1.16/30 IRBs though ,,,so there is connectivity

     

    When I go to config my rip neighbors, I'm presented with my ae links as such:

    Below that is my rip config on the 4600  -the other side - 3300 is simlilar.

     

    I know fundementally this will work -- it does w Cisco .. I'm sure there's something "Junos" I'm missing !

     

    oot@Campus_Core# set protocols rip group ths neighbor ?
    Possible completions:
    <neighbor_name> Interface name
    ae0.0 Interface name
    ae1.0 Interface name
    ae2.0 Interface name
    ae3.0 Interface name
    ae4.0 Interface name
    ae5.0 Interface name
    ae6.0 Interface name
    ae8.0 Interface name

     

    rip {
    group ths {
    export rip_export;
    neighbor ae0.0;
    neighbor ae1.0;
    neighbor ae2.0;
    neighbor ae3.0;
    neighbor ae5.0;
    neighbor ae6.0;
    neighbor ae8.0;
    neighbor ae4.0;

     

    }
    policy-statement rip_export {
    term connected {
    from protocol direct;
    then accept;
    }
    term static {
    from protocol static;
    then accept;
    }
    term rip {
    from protocol rip;
    then accept;
    }
    term default {
    then reject;
    }

     



  • 7.  RE: Layer 2 broadcast domain over layer 3 routed links

    Posted 08-22-2018 17:26
    Disregard the last post. I realize now I need to specify the newly created vlan interface (vlan.xxx or irb.xxc) as my rip neighbor, not the ae interface which is now a trunk.

    Thanks all


  • 8.  RE: Layer 2 broadcast domain over layer 3 routed links

     
    Posted 08-22-2018 21:19
    Glad it’s working! If you are running spanning tree everywhere you should consider using mstp or vstp so that your irb-based uplinks don’t become collateral damage if a recalc on the spanned vlan decides to block one of the core uplinks.


  • 9.  RE: Layer 2 broadcast domain over layer 3 routed links

    Posted 08-16-2018 02:08

    Hello

    Assuming Your core switches are EX4300/4600, and access switches are 3300 (not the other way around) then You have 2 choices:

    1/ classic way : reconfigure core switches' interlinks to be mixed L2/L3 links, where L2 will be serving Your broadcast VLAN(s)

    2/ bleeding edge way : use EVPN-VXLAN on EX4300/4600 to forward Ethernet frames on L2 over routed core links

    https://www.juniper.net/documentation/en_US/junos/topics/concept/evpn-vxlan-data-plane-encapsulation.html  

    Make sure You understand the EVPN-VXLAN implementation limitations on EX4600:

    https://www.juniper.net/documentation/en_US/junos/topics/concept/vxlan-constraints-qfx-series.html 

    GRE on EX product has limited performance (think KPPS and not MPPS) but if Your broadcast domain does not need MPPS then You might get away with it.

    HTH

    Thx

    Alex



  • 10.  RE: Layer 2 broadcast domain over layer 3 routed links

    Posted 08-17-2018 06:47
      |   view attached

    Thanks for the response and info.... aarseniev

     

    When you say mix your links, you mean phyiscailly I assume?..... there's no way to do that logially is there? I suppose the tunneling is what I'm after. If I use GRE....would I be able to selctivily only bridge a single vlan from each site (vlan 505 in my case)?...and leave the other existing vlans as is....routing via the L3 links. ??

     

    I attached a pdf visio of what I'm looking at..... I really do appreciate your time if you an take a quick look.

    Thanks...Dennis

     

     

    Attachment(s)