Juniper trunking with two links (not using LAG)

Question

Some reason I'm drawing a blank on this. Let's say I have two EX switches connected together with 2 links to each other (xe-0/1/0 and xe-0/1/1 on both switches).

I can easily setup a trunk on one of those links using a simple configuration like the following:

test@SW1# show interfaces xe-0/1/0                                 
unit 0 {
description "Trunk to SW2 to port xe-0/1/0";
family ethernet-switching {
    port-mode trunk;
    vlan {
        members [ vlan-10 vlan-20 ];
    }
    native-vlan-id 1;
}
}

Now my question is how would I make the second link be a backup for this trunk? Would I configure port xe-0/1/1 the same as above and let STP block it? What's the proper procedure for this?

From what I can tell there are 3 options (redundant trunk group, link aggregation, two links using STP) I'm just having an issue telling if I need to configure both ports identically or if there is something else I should do.

Thanks!

Answer 1

One thing to keep in mind with trunk redundancy is that STP fails over slowly, even with Rapid STP. If you set up the two links as an aggregated channel, the link failover is much faster. STP failover is the slowest, routing protocol failover is an order of magnitude faster, and the aggregation channel failover is another order of magnitude faster still.

Answer 2

RSTP - configure both links the same. Ensure that RSTP is enabled on both sides of the link via 'set protocols rstp interface xe-blah' or just ensure 'set protocol rstp interface all' is configured.

RTG - Must explicitly disable RSTP. RTG and RSTP are mutually exclusive. Once RSTP is disabled configure both links the same but also provide the RTG group configuration under ethernet-switching options - (http://www.juniper.net/documentation/en_US/junos13.2/topics/example/cfm-ex-series-redundant-trunk-groups.html)

Link aggregation - Create aggregated ethernet interface, the trunk configuration goes under the aggregated ethernet interface while the physical members will just be configured to be members of the AgEth bundle.

Example:

set chassis aggregated-device ethernet device-count 1
!
test@SW1# show interfaces ae0                               
unit 0 {
description "Trunk to SW2:ae0";
aggregated-ether-options {
lacp {
active;
}
}
family ethernet-switching {
    port-mode trunk;
    vlan {
        members [ vlan-10 vlan-20 ];
    }
    native-vlan-id 1;
}
}

set interfaces xe-0/1/0 gigether-options 802.3ad ae0
set interfaces xe-0/1/1 gigether-options 802.3ad ae0

Link aggregation would be preferred as RSTP and RTG are an active/standby configuration by default. Whereas with link aggregation you could make use of both paths and have automatic failover with no STP like delay should a link fail.

HTH