JNCIS-SP: Bridge domain Enterprise style.

MX-series routers are excellent switches and configuration-wise, though different from EX-switches, not that cumbersome.
To demonstrate some basic configuration of the MX, I will use the following setup;



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I started out with the EX4500’s port configuration, which I kept as basic as it gets. I configured a trunk for all vlans and a vlan with a layer 3 interface;



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Let’s enable the same configuration on the MX router:



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Since I had already activated ‘encapsulation flexible-ethernet-services’ and ‘vlan-tagging’, this basic configuration enabled connectivity between the two devices;



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This configuration provides for a bridge domain with all the default values. A lot of these default values can be changed on the global, switch, bridge-domain or interface level. Let’s look at ways to change the default values. I’ll change the:

    • global mac-limit from 393215 to 300000. This applies to all bridge domains.
    • bridge-domain mac limit from 5120 to 6000, with a packet action of drop (default is to forward the frame and simply not learn the mac-address).
    • interface mac limit to from 5120 to 3000



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Besides changing the properties of the mac-table size, there are more options you can change. You can, for example, alter the mac aging-time (or disable mac-learning all together).
In case you want to alter the values for a routing-instance of the type virtual-switch, simply configure the [ edit switch-options].

The MX-series routers also support stp, rstp, mstp and vstp. Contrary to the EX4500, none of these protocols are activated by default, nor are they activated upon the creation of a bridge-domain. This can be seen on the EX4500;



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Since the EX4500 is running vstp, lets activate this on the MX80 and activate some basic options as well. The MX80 will;
    • have a priority of 4k
    • associate a cost of 20000 with the xe-0/0/0 interface
    • not allow for the port to become a root-poort



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The EX4500 will start listing the MX80 as root:



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The MX-side can be examined with the following commands:



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Let’s observe what happens when we trigger the ‘no-root-port’ by configuring ‘set protocols vstp vlan 90 bridge-priority 0’ on the EX4500:



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As soon as the MX80 stops receiving superior BPDUs on that interface, the port will transition to forwarding again.
This was the Enterprise style configruation of briding on the MX series routers. For the Service prodivider tyle, check here.

30-8-2014