[nsp] Re(2): Native VLAN?

From: Angelo De Guzman (a.deguzman@wesolv.com.ph)
Date: Fri Feb 08 2002 - 02:40:00 EST


Thanks for the reply! 8-)

    I have a follow up question regarding these native
VLAN.I have a client who has two 6509 and the connection
in between the two is through a trunk port. What keeps
me wondering is that each VLAN 1 one on both switch has
a different ip network.

Set-up:

                 Cisco_ 3640
                 / \
               / \
             / \
           / \
         / \
      7206_Old 7206_New
         | 192.168.21.2 |
         | |
         | |
      Catalyst6509A --(trunk)-------Catalyst6509B

Sample Config:

Catalyst6509A

interface Vlan 21
  ip address 192.168.21.1 255.255.255.0

Catalyst6509B

interface Vlan 21
  ip address 197.77.77.1 255.255.255.0

  Why dont I get errors on these? Like conflict vlan
id or something weird..(just guessing). I also notice
that when I try to ping from Catalyst6509A the ip
address 197.77.77.1 it goes around the network first.
Meaning the next hop is from another router.
(I assumed that it would be one hop away because
of the trunk connection!!!)
  Now this is the tricky part, I wanted to implement
HSRP. Since 192.168.21.2 is the default gateway it
would be the virtual ip address for the HSRP. Is this
possible? Especially with VLAN 21 of Catalyst 6509
belongs to a different network. (i'm thinking of
assigning 197.77.77.0 to a different vlan and re-assigning
Vlan 21 0f Cat__B to 192.168.1.x). What is important for
me to achieve right now, is for users in the Catalyst 6509A
would be able to access the 3640 router even if 7206_Old is down.
TIA,
Angelo
Nash Darukhanawalla (2/8/02 9:58 AM):
>Angelo,
>
>A trunk port configured with 802.1Q tagging can receive both tagged and
>untagged traffic. By default, the switch forwards untagged traffic with the
>native VLAN configured for the port. The native VLAN is VLAN 1 by default
>or is the vlan that the port was a member of before it was configured as a
>trunk.
>
>If a packet has a VLAN ID the same as the outgoing port native VLAN ID, the
>packet is transmitted untagged; otherwise, the switch transmits the packet
>with a dot1q tag.
>
>"encapsulation isl 1 native" essentially configures VLAN 1 that is sending
>and receiving untagged traffic on the trunk port.
>
>We do not care about the native vlan when encapsulation is isl because all
>packets are tagged. But that's not the case with dot1q encap and so native
>vlan should match at both the ends of the link.
>
>-- Nash
>
>
>At 09:24 AM 2/8/2002 +0800, Angelo De Guzman wrote:
>>Hi To All,
>> I'm using 2948G-L3.
>> interface port-channel 1.1
>> encapsulation isl 1 native
>> What does it mean when the native command is added? Please enlighten me on
>>this matter!
>>TIA,
>>Angelo
>



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