Simple bridging on MX

29 10 2014

I’m doing some studying using Junosphere at the moment, but unfortunately Junosphere can’t emulate a LAN at the moment.  Basically the same problem that GNS3 has and (as far as I know) Cisco’s VIRL/CML has as well.  So you’ve got to bodge it with Integrated Routing and Bridging (IRB).   What I needed topology-wise was this:

LAN segment between S1, R1 and R2

LAN segment between S1, R1 and R2

I find Junos a bit counter-intuitive when creating bridge domains.  Here I need something quite simple – two ports in a bridge group (no VLANs or anything), but I need to give a VLAN tag value to identify the bridge domain.

Anyway, the process for doing this is as follows:

1. Give the physical interfaces the right encapsulation type – ethernet-bridge

2. Create a bridge domain which has a VLAN-ID and references these two interfaces

3. Create an IRB interface (irb.10) with family inet and an IP address on it

4. In the bridge domain, use “routing-interface irb.10” to tie the bridge domain and the IP interfaces together.

The result is this:

IRB solution for LAN

IRB solution for LAN

The configuration I used was this:

root@S1# show interfaces
ge-0/0/0 {
    description "to R1 0/0/1";
    encapsulation ethernet-bridge;
    unit 0;
ge-0/0/1 {
    description "to R2 0/0/3";
    encapsulation ethernet-bridge;
    unit 0;
irb {
    description "to R1 and R2";
    unit 10 {
        family inet {

root@S1# show bridge-domains
    domain-type bridge;
    vlan-id 10;
    interface ge-0/0/0.0;
    interface ge-0/0/1.0;
    routing-interface irb.10;



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