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Problems with QoS between 2950 and 3550 with use of Native VLAN

Hi!

I try to set up QoS between a C2950 and a C3550, I have provided a drawing that might help understanding the setup.

As I understand it, since I only have the SMI image on the C2950 I have to run a 802.1Q trunk over the leased 2Mb line to get QoS to work. And I DO get it to work, or at least it seems so to me.

What I'm trying to setup QoS on is between a Nortel Succession Media Server and a Nortel i2004 IP Phone.

And when I sniff the port that the Succession Media Server is connected to, I get this output:

*BEGIN*

*** TO IP Phone ***

IP version: 0x04 (4)

Header length: 0x05 (5) - 20 bytes

Type of service: 0xB8 (184)

Precedence: 101 - CRITIC/ECP

Delay: 1 - Low delay

Throughput: 1 - High throughput

Reliability: 0 - Normal reliability

Total length: 0x00C8 (200)

ID: 0x5FE1 (24545)

Flags

Don't fragment bit: 0 - May fragment

More fragments bit: 0 - Last fragment

Fragment offset: 0x0000 (0)

Time to live: 0x40 (64)

Protocol: 0x11 (17) - UDP

Checksum: 0x69EC (27116) - correct

Source IP: 10.40.2.10

Destination IP: 10.10.153.100

IP Options: None

UDP

Source port: 5216

Destination port: 5200

Length: 0x00B4 (180)

Checksum: 0x5C02 (23554) - correct

*** FROM IP Phone ***

IP version: 0x04 (4)

Header length: 0x05 (5) - 20 bytes

Type of service: 0xB8 (184)

Precedence: 101 - CRITIC/ECP

Delay: 1 - Low delay

Throughput: 1 - High throughput

Reliability: 0 - Normal reliability

Total length: 0x00C8 (200)

ID: 0x8285 (33413)

Flags

Don't fragment bit: 0 - May fragment

More fragments bit: 0 - Last fragment

Fragment offset: 0x0000 (0)

Time to live: 0x7F (127)

Protocol: 0x11 (17) - UDP

Checksum: 0x0848 (2120) - correct

Source IP: 10.10.153.100

Destination IP: 10.40.2.10

IP Options: None

UDP

Source port: 5200

Destination port: 5216

Length: 0x00B4 (180)

Checksum: 0x5631 (22065) - correct

*END*

But, then to the problem:

Since the modems I use have ip adresses in them I want to monitor them and be able to change settings in them.

But to connect to units within the trunk, I have to set the native vlan to VLAN 144, which provides the ip adresses I use for the modems, in both ends of the trunk.

But if I do that the tagging of the packets from the IP Phone disappears!

Here's an output after native VLAN is applied:

*BEGIN*

*** TO IP Phone ***

IP version: 0x04 (4)

Header length: 0x05 (5) - 20 bytes

Type of service: 0xB8 (184)

Precedence: 101 - CRITIC/ECP

Delay: 1 - Low delay

Throughput: 1 - High throughput

Reliability: 0 - Normal reliability

Total length: 0x00C8 (200)

ID: 0xDEF8 (57080)

Flags

Don't fragment bit: 0 - May fragment

More fragments bit: 0 - Last fragment

Fragment offset: 0x0000 (0)

Time to live: 0x40 (64)

Protocol: 0x11 (17) - UDP

Checksum: 0xEAD4 (60116) - correct

Source IP: 10.40.2.10

Destination IP: 10.10.153.100

IP Options: None

UDP

Source port: 5240

Destination port: 5200

Length: 0x00B4 (180)

*** FROM IP Phone ***

IP version: 0x04 (4)

Header length: 0x05 (5) - 20 bytes

Type of service: 0x00 (0)

Precedence: 000 - Routine

Delay: 0 - Normal delay

Throughput: 0 - Normal throughput

Reliability: 0 - Normal reliability

Total length: 0x00C8 (200)

ID: 0x89E4 (35300)

Flags

Don't fragment bit: 0 - May fragment

More fragments bit: 0 - Last fragment

Fragment offset: 0x0000 (0)

Time to live: 0x7F (127)

Protocol: 0x11 (17) - UDP

Checksum: 0x01A1 (417) - correct

Source IP: 10.10.153.100

Destination IP: 10.40.2.10

IP Options: None

UDP

Source port: 5200

Destination port: 5240

Length: 0x00B4 (180)

Checksum: 0x31CA (12746) - correct

*END*

See, there is noe QoS tagging from the IP Phone anymore.

If I set no switchport trunk native vlan 144 in both ends the tagging is back.

Any ideas? Is this a bug, or just some command I don't know about?

Please take a look at the picture to get a more understandable view of the setup.

Thanks!

1 REPLY 1
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Beginner

Re: Problems with QoS between 2950 and 3550 with use of Native V

Well, native VLANs are by definition untagged so there´s nothing wrong with that as far as you are getting the expected results. By the other way I think you should include VLAN 402 on your allowed vlan range on Catalyst 3550's FastEth0/45 trunk port, otherwise this VLAN will be completly isolated from the rest of the network.

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