Re: Tagged and Untagged ports
- From: sowmyatv@xxxxxxxxx
- Date: Tue, 8 Jan 2008 11:38:42 -0800 (PST)
On Jan 8, 11:55 am, Sam Wilson <Sam.Wil...@xxxxxxxx> wrote:
In article
<67936995-f6c9-4627-b247-b895d29ad...@xxxxxxxxxxxxxxxxxxxxxxxxxxx>,
sowmy...@xxxxxxxxx wrote:
Hi,
I have the following setup - Cisco 2950 switch, 4 of its ports
(fa20, 21, 22, 23) are bundled as a port-channel (po1). The po1 is a
trunk that carries multiple VLANs 3,4,5,6 and is connected to another
non-cisco switch's port-channel. Another port (fa17) on cisco is an
access port whose default VLAN is 3. This is the uplink port that goes
out to the internet.
Problem : Does not work. Looks like the access port does not know how
to send the traffic to the po1 and vice versa. Note: If I change the
port fa17 to be a trunk port and tag it with 3 and pump tagged
traffic, it works. If I untag both po1 and fa17 and make 3 to be
default, it works. The problem is only when I have tagging on one side
and default vlan untagged on the other. Am I missing something here?
The configuration looks OK for what you describe, though I'd be more
confident if I knew the LACP was connecting properly, but I'm wondering
if the non-Cisco switch is doing what you think it is. Here's my guess:
The fact that the setup works when both ports are untagged means that
the traffic is arriving *untagged* from the non-Cisco. That means it's
not arriving as tagged on VLAN 3, it's arriving on the default (native)
VLAN, VLAN 1 unless you specify otherwise, and you haven't. It works
when both ports are tagged, but that will be because both ports are
carrying VLAN 1 untagged.
I think you need to check the setup of the non-Cisco switch and see what
VLANs are tagged and untagged on its connection.
Sam
Hi Sam,
Thanks a lot for the reply. I am trying to isolate the problem. I
removed the Port-channel from the Cisco, removed the other non-cisco
switch too.
I made 1 port on Cisco to be access port and another port to be trunk
port.
For eg. fa0/17 - access port - access vlan 101
fa0/18 - trunk port - allowed vlan 101, dot1q encapsulated,
trunk mode
Connect 17 to Host 1 (mimics uplink here)
Connect 18 to Host 2 (mimics the portchannel in the previous scenario)
Host 2 has an interface thats tagged on 101 and has an IP say
192.168.101.100
Host 1 has an untagged interface that has an IP say 192.168.101.101
Now I ping from 192.168.101.101 to 192.168.101.100 and vice versa.
My configuration is
interface FastEthernet0/17
switchport access vlan 101
switchport mode access
!
interface FastEthernet0/18
switchport trunk encapsulation dot1q
switchport trunk allowed vlan 101
switchport mode trunk
!
Anything wrong with this config? Why is my ping not working.
Note: it works if both 17 and 18 are tagged(trunk), or ports 17 and 18
are untagged(access with default VLAN 101). But not if one tagged and
one untagged.
My understanding was that when 17 receives untagged packets from Host
1, since its default vlan is 101, its supposed to tag it when it sends
to 18 which is tagged.
Correct me if wrong. I appreciate ur help.
thanks
Sowmya
.
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