native vlan

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Joined: 12 Jun 2017 03:21

native vlan

Post by capitanGiaco » 21 Dec 2017 12:31


what are the contraindications to use different native vlan ids on the 802.1q trunk ports ?
For example I set the vlan untagged on the 10K port, and left the default (1) vlan on all the ports of the remote switch (6250):

show vlan members port 1/1
vlan type status
10 default forwarding
25 qtagged forwarding
60 qtagged forwarding

show ip interface:
vlan10 UP YES vlan 10

Remote (6250)
show vlan port 1/1
vlan type status
1 default forwarding
25 qtagged forwarding
60 qtagged forwarding

show vlan 1 port
port type status
1/1 default forwarding
1/2 default inactive
1/3 default forwarding
1/4 default forwarding
1/5 default forwarding

the vlan 10 works in every ports of the 6250 (and also the other vlans, where the device use tagging).

What are the pros and cons of using this kind of configuration instead of just use the tag on the trunk ports and the default vlan in all remote switch ports ?

PS: the same config worked also in 7800 and 9800 (my precedent central l3 switches)



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Re: native vlan

Post by devnull » 27 Dec 2017 03:40

What do you try to achive?
What you do is you couple traffic in vlan 10 (OS10k) with vlan 1 (6250) this works because traffic without tags is assigned the native vlan.

Same would work if you use vlan 10 native on all port of the 6250 - or native vlan 1 on the OS10k. I would prefer a setting like that, this makes it more visible what vlans contain the same traffic

Posts: 6
Joined: 01 Dec 2017 04:56

Re: native vlan

Post by David_Klancar » 12 Jan 2018 11:40

Hi Giacomo,

I totally agree with devnull, it's better to keep vlan numbers consistent between switches. You might see strange things as LLDP remote-system information, because the vlan can be sent in the TLV, therefore you'll see both neighbors talking to each other but on different vlan:

Remote LLDP nearest-bridge Agents on Local Port 1/1/28:

Chassis e8:e7:32:d7:99:55, Port 1020:
Remote ID = 64,
Chassis Subtype = 4 (MAC Address),
Port Subtype = 7 (Locally assigned),
Port Description = Alcatel-Lucent OS6900 XNI 1/1/20,
System Name = SWITCH
System Description = Alcatel-Lucent OS6900-X20 GA, August 24, 2015.,
Capabilities Supported = Bridge Router,
Capabilities Enabled = Bridge Router,
Management IP Address =,
Remote port default vlan = 1,
Vlan ID = 1,
Vlan Name = VLAN 1,
Protocol vlan Id = 0 (Flags = 0),
Protocol Identity = 88cc,
Remote port MAC/PHY AutoNeg = Supported Disabled Capability 0x0000,
Mau Type =10GigBaseSR - R fiber over 850 nm optics

Remark: because of same behavior with Cisco swiches using CDP (instead of LLDP), you'll get 'Native VLAN mismatch' error logs...

Besr regards


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