5

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!

3

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.

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  • The issue I'm having is actually with using (r)STP or RTG configuration wise. Would I configure both ports to be trunked like in my example (identical)? I believe I tried that with no luck however it could have been a mistake on my end. – WinkyWolly Oct 15 '15 at 21:57
  • Sorry, I'm not a Juniper guy. In the Cisco world, you can configure them identically, and STP would take care of it. – Ron Maupin Oct 15 '15 at 22:04
  • That's what I thought too - I'll give that a whirl again. Perhaps it was an silly issue on my end. – WinkyWolly Oct 15 '15 at 22:11
3

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

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  • To build on an already great answer - you should run spanning-tree even if you opt for the aggregated ethernet method. This ensures that if the two switches are later connected together on another pair of ports that you will not experience a loop and broadcast storm – Benjamin Dale Mar 18 '18 at 21:40

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