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I plan to replace a Juniper EX4200 that was configured a vlan default gateway, for less downtime, I will setup a new EX4200, copy configuration and transfer network cables from the old switch.

But if the new switch online, it will be two duplicate gateway ip exist on the network, the routing will be failed, how can I fixed this problem? Thanks

  • Did any answer help you? if so, you should accept the answer so that the question doesn't keep popping up forever, looking for an answer. Alternatively, you could provide and accept your own answer. – Ron Maupin Aug 11 '17 at 3:26
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To be clear, there are two sub-issues worth identifying--the gateway and the ports. Moving the ports is relatively easy if you connect the two switches together via an ethernet-switching port (I personally use trunks between all switches), copy the remaining port configurations over, then move cables one-at-a-time. This lets you control which ports (and potentially users/services) go down at what time.

The best answer for the gateway is to setup VRRP for that gateway, but it still will require 2 short down times, and has enough configuration gotchas that it may not be worth the time invested. I suggest trunking the two switches together, then simply remove the vlan from one and add it to the other. Using Juniper for both switches, you get the advantage of the commit button. Load your command set on each, the just commit on the first, wait until it completes, then commit on the second. Failback is just as easy: rollback on new, wait, rollback on old.

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As others have said, you'll want to utilize VRRP to get one ready for the transition. Since you're using the vlan subinterface as the gateway for your vlan, you'll want a configuration similar to below.

Here are sample configurations for the master that I stood up.

rj@MHN00528CAN01# show interfaces vlan.1
family inet {
    address 10.1.1.2/24 {
        vrrp-group 1 {
            virtual-address 10.1.1.1;
            priority 254;
            fast-interval 100;
            preempt;
            accept-data;
            advertisements-threshold 10;
        }
    }
}

And an example of the backup.

rj@MHN00528AN02# show interfaces vlan.1
family inet {
    address 10.1.1.3/24 {
        vrrp-group 1 {
            virtual-address 10.1.1.1;
            priority 126;
            fast-interval 100;
            preempt;
            accept-data;
            advertisements-threshold 10;
        }
    }
}

Take note of the priorities as the higher, the more preferable a master it will be. One thing that always screwed with me was the accept-data configuration statement. A VRRP speaker will not accept data on a virtual address unless it has that explicitly configured, or if the virtual address is the same as the interface address.

Now verify that the master is talking.

rj@MHN00528CAN01> show vrrp brief
Interface     State       Group   VR state VR Mode   Timer    Type   Address
vlan.1        up              1   master   Active      A  0.043 lcl    10.1.1.2
                                                                vip    10.1.1.1

Then ensure the backup sees the master advertising.

rj@MHN00528AN02> show vrrp brief
Interface     State       Group   VR state VR Mode   Timer    Type   Address
vlan.1        up              1   backup   Active      D  0.994 lcl    10.1.1.3
                                                                vip    10.1.1.1
                                                                mas    10.1.1.2

From the configuration statements above (taking into account the fast-interval and advertisements-threshold values) you would achieve a 1 second failover time. Depending on your environment and how critical this vlan is, you may want less or more.

  • Thanks. I think this is the best way in my case. It just some seconds downtime when I commit vrrp. And thanks you guys for a great help. – TmT TMi Feb 7 '15 at 16:55
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...and transfer network cables from the old switch.

If you move the cabling from the currently active switch to the new switch, the new switch will become the only available gateway on the network since the old switch no longer has any cables connected.

I suggest configuring the new EX4200 without cables connected(except console) and when you are done, shut the old one down, remove all cables from the old switch and plug them into the new. To minimize downtime keep the new switch running before you shut the old one down.

However you approach this you will not be able to make the swap without network down-time.

If this does not answer your question, please try to describe in more detail what issue you are facing.

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