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VLAN Tagging on Cisco 2924 Switch

Posted on 2011-03-06
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Last Modified: 2012-05-11
I am trying to troubleshoot a device connectivity issue which consists of a CPE which tags traffic on it's WAN interface with VLAN 35. I can see the tag in a Wireshark capture. According to the vendor, I need to configure the switch to tag the traffic on VLAN 35 for the WAN interconnect & then strip the VLAN tag on the interface that will send traffic outbound from the switch. So, basically, CPE WAN port connects to tagged port on the 2924 (port 1) and then traffic leaving the switch on port 13 will strip the tag. I've been trying to get this working but just having a whale of a time.

If I do a packet capture I see the DHCP requests with an 802.1Q section with the ID of 35.

Any ideas? The switch is running older code - 12.0(5.4).

The engineer for the device followed up with this:

"Cisco2924 should work for this.

Setup one port on 2924 as 802.1Q Trunking port and connect it to R1000H WAN Ethernet.

Setup one port on 2924 with ingress VLAN tag 35 (egress traffic shouldn’t have any VLAN) and connect it to HDM."

I can setup the 802.1Q trunking port - what exactly is the configuration for the other ingress port?

Thanks,

-Samson
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Question by:smartinez1984
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Accepted Solution

by:
lrmoore earned 500 total points
ID: 35050133
Is it a layer 3 connection with an IP address?
I have a similar setup:

vlan 35
interface vlan 35
 ip address 1.2.3.1 255.255.255.0
!
interface fast 0/2
 switch trunk encap dot1
 switch mode trunk
 switch trunk allow vlan 35

There is no additional port configuration needed for other ports, only the one connected to the R1000H
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LVL 79

Assisted Solution

by:lrmoore
lrmoore earned 500 total points
ID: 35050195
Never mind about the vlan interface. Not available on the 2924. Your L3 has be routed someplace else.
You can also add other ports to the same vlan 35, but as access ports.
interface fast 0/4
 switch access vlan 35

I guess this would be what they qualify as egress ports.
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Author Comment

by:smartinez1984
ID: 35051876
Well, no...

Basically, here is the situation. The CPE is broadcasting for a DHCP address. However, the device is also tagging the frames with VLAN 35 ID.

The vendor is saying we have to tag the inbound interface by using a DOT1Q trunk. However, the outbound interface, while configured as an access port on VLAN 35, has to strip the tag.

That's where i'm having difficulty. I've tried creating the outbound interface with the native VLAN assigned as 35 but packet captures upstream still show the tag applied. Which apparently causes problems.

So, in a nutshell, I need to have the port that connects to the CPE as a DOT1q trunk and the outbound interface on the same switch has to strip the tag.

-Samson
0
 

Author Comment

by:smartinez1984
ID: 35057655
Got it working. Configured the CPE interconnect as a trunk:

switchport trunk encapsulation dot1q
switchport mode trunk
spanning-tree portfast

Then configured the outbound interface (connecting to upstream switch) as follows:

switchport access vlan 35

So, yea, right track... :)
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