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Community Member

Native VLAN in InterVLAN routing

Hi Experts,

I am testing the InterVLAN routing using a router in stick mode doing VLAN routing between VLAN 2 & VLAN 3. These two VLANs are configured in a Layer 2 switch connecting this ROUTER-1 and Hosts

say HOST-2 and HOST-3

ROUTER-1 fa 0/0 is configured with subinterface fa0/0.3 & fa 0/0.2 and the configuration is

interface fa 0/0.2

ip add 192.168.2.1 255.255.255.0

encapsulation dot1Q 2

interface fa 0/0.3

ip add 192.168.3.1 255.255.255.0

encapsulation dot1Q 3

It is working perfectly in this configuration routing between VLAN 2 & VLAN 3

If I add keyword native to either "encapsulation dot1Q 2" or "encapsulation dot1Q 2", I am not able to reach from VLAN 2 to VLAN 3.

I learned that "The native VLAN is used for untagged traffic when the port is in 802.1Q trunking mode"

How it is conflicting in our scenario. I expected that whenever the packet comes without VLAN tag only those packets will be tagged with either VLAN 2 or VLAN 3.

Can you please take your valuable time in explaning this?

regards,

sairam

1 ACCEPTED SOLUTION

Accepted Solutions
Hall of Fame Super Silver

Re: Native VLAN in InterVLAN routing

Hello Sairam,

you have used a different account for this reason you cannot flag as solved the answer.

but don't worry about this.

>> So, I will presume that native keyword can be used only in one of the sub-interface and not in all.

correct

Hope to help

Giuseppe

9 REPLIES

Re: Native VLAN in InterVLAN routing

Hi,

VLAN1 is the native on your switch trunk port by default.

I.e., if you add native keyword in your router subinterface configuration, you are connecting the L3 subinterface to VLAN1 on the switch in fact.

And that's why you are losing your connectivity.

BR,

Milan

Hall of Fame Super Silver

Re: Native VLAN in InterVLAN routing

Hello Sairam,

the two sides of the trunk have to agree on the native vlan vlan#.

default settings is native vlan=1 on both routers and switches.

if you add the native option only on the router side the switch will treat the received frames as belonging to vlan1 not vlan2 or vlan3.

As a result you will have IP connectivity issues.

the native option is useful when connecting to a device with a non default native vlan.

Hope to help

Giuseppe

Community Member

Re: Native VLAN in InterVLAN routing

Hi Giuseppe,

Thanks for your reply. yes I tried configuring native VLAN 2 on the trunk port of the switch connecting to Router. It is working perfectly.

But If I do the same thing on Fa0/0.3 with command "encapsulation dot1q 3 native", it stopped working.

I realised the reason that I have option of configuring only one Native VLAN in one trunk port. Since I configured native VLAN as VLAN 2, VLAN 3 also as native VLAN

I may be little messing the concept.Pl. bare with me

I appreciate your valuable comments.

sairam

Hall of Fame Super Silver

Re: Native VLAN in InterVLAN routing

Hello Sairam,

>> I realised the reason that I have option of configuring only one Native VLAN in one trunk port

this is correct.

I think that if you later configure f0/0.3 native the native option is removed from f0/0.2 on router side and you have a native vlan mismatch with the switch port.

you can check this with

sh run int f0/0.2

before and after having added the native option to f0/0.3

Hope to help

Giuseppe

Community Member

Re: Native VLAN in InterVLAN routing

Hi Giuseppe,

Indeed I tried that even before. No info is shown as like Cisco switches. The output I am pastin here

R0#sh int fa 0/0.1

FastEthernet0/0.1 is up, line protocol is up

Hardware is AmdFE, address is cc00.0094.0000 (bia cc00.0094.0000)

Internet address is 192.168.1.1/24

MTU 1500 bytes, BW 100000 Kbit/sec, DLY 100 usec,

reliability 255/255, txload 1/255, rxload 1/255

Encapsulation 802.1Q Virtual LAN, Vlan ID 5.

ARP type: ARPA, ARP Timeout 04:00:00

Last clearing of "show interface" counters never

regards,

sairam

Hall of Fame Super Silver

Re: Native VLAN in InterVLAN routing

Hello Sairam,

on routers sh vlan or sh vlans can tell you this:

sh vlans

Virtual LAN ID: 1 (IEEE 802.1Q Encapsulation)

vLAN Trunk Interface: FastEthernet0/0

>> This is configured as native Vlan for the following interface(s) :

FastEthernet0/0

Protocols Configured: Address: Received: Transmitted:

Other 0 41275

18869 packets, 4488731 bytes input

41275 packets, 2931074 bytes output

Virtual LAN ID: 10 (IEEE 802.1Q Encapsulation)

vLAN Trunk Interface: FastEthernet0/0.10

Protocols Configured: Address: Received: Transmitted:

IP 10.99.78.1 12392643 15716578

Other 0 13243

Hope to help

Giuseppe

Community Member

Re: Native VLAN in InterVLAN routing

Hi Giuseppe,

Yes I am able to find this.

Thanks for your help. I am not able to see the menu to indicate that the issue is resolved. Thus,I am expressing my thanks here.

So, I will presume that native keyword can be used only in one of the sub-interface and not in all.

sairam

Hall of Fame Super Silver

Re: Native VLAN in InterVLAN routing

Hello Sairam,

you have used a different account for this reason you cannot flag as solved the answer.

but don't worry about this.

>> So, I will presume that native keyword can be used only in one of the sub-interface and not in all.

correct

Hope to help

Giuseppe

Community Member

Re: Native VLAN in InterVLAN routing

Native VLAN can be only one on a switch and when configuring on two different switches so both the Native VLAN must be same on both side.

Now in ur case when u using "encapsulation dot1q native" on router so make sure u define on switch also becoz vlan1 is native by default and when data recieve so it is for VLAN2 or 3 so mistmatch and u can not communicate.

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