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  • 1.  Layer 3 routing and trunking between two juniper EX3400 switches

    Posted 02-21-2022 05:44

    I have two Juniper EX3400 switches that support layer 3 routing as well. I want to create a layer 3 routing on one switch and want to use a second switch as an access switch. Both switches are connected via fiber link, on both switches uplink ports are set in trunk mode with the blue vlan allowed.

    On switch 1, if I add any port in access mode and allow the blue vlan it will automatically assign IP address to the connected devices (such as 10.0.0.6). But on the second switch (SW2) is not directly getting the IP address from the first switch although three-ports is set in access mode and theoretically it should be getting IP addresses 10.0.0.2, 10.0.0.3, 10.0.0.4 respectively. 

    Here are the configuration details. Please tell me is there anything else that needed to be on switch two to make things work. Is layer 3 trunking is different from layer 2 trunking as I can only see tutorials of layer 2 trunking on the internet?

    Switch 1:

    set vlans blue vlan-id 100

    set vlans blue l3-interface vlan.100

    set interfaces irb unit 100 family inet address 10.0.0.1/24

    set interfaces ge-0/0/0 unit 0 family ethernet-switching vlan members blue

    Set Switch 1 fiber link to trunk mode and allow the Blue VLAN

    set interfaces xe-0/2/0 unit 0 family ethernet-switching interface-mode trunk

    set interfaces xe-0/2/0 unit 0 family ethernet-switching vlan members blue

    Switch 2:

    set vlans blue vlan-id 100

    set vlans blue l3-interface vlan.100

    set interfaces ge-0/0/0 unit 0 family ethernet-switching interface-mode access

    set interfaces ge-0/0/0 unit 0 family ethernet-switching vlan members blue

    set interfaces ge-0/0/1 unit 0 family ethernet-switching interface-mode access

    set interfaces ge-0/0/1 unit 0 family ethernet-switching vlan members blue

    set interfaces ge-0/0/2 unit 0 family ethernet-switching interface-mode access

    set interfaces ge-0/0/2 unit 0 family ethernet-switching vlan members blue

    Set Switch 2 fiber link to trunk mode and allow the Blue VLAN

    set interfaces xe-0/2/0 unit 0 family ethernet-switching interface-mode trunk

    set interfaces xe-0/2/0 unit 0 family ethernet-switching vlan members blue





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    Abdul Qurashi
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  • 2.  RE: Layer 3 routing and trunking between two juniper EX3400 switches

    Posted 02-25-2022 12:25
    VLAN trunking is always L2. If you simply want to extend the VLAN you don't need to setup L3 on the second switch (ie no "set vlans blue l3-interface vlan.100" is needed on switch 2). Based on your stated intention you want an L2 config with the L3 gateway on switch 1.

    I'd try taking the l3 interface off of switch 2. Then see if DHCP works. If not try manually setting an IP on the device connected to switch 2 and ping the GW. If that works then it's a DHCP issue, if not then you'll need to debug your trunk further.


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    Allyn Crowe
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