Juniper EX2300 QinQ questions

juniperjuniper-exqinq

I am trying to set up a Q in Q environment with EX2300(ELS). Unfortunately, I receive the error message down below when I enter commit check

[edit interfaces ge-0/0/0]
  'unit 0'
     VLAN-ID must be specified on tagged ethernet interfaces
error: configuration check-out failed

The Q in Q config which I followed right here:
https://www.juniper.net/documentation/en_US/junos/topics/task/configuration/qinq-tunneling-qfx-series-els.html

Also post my config of interfaces ge-0/0/0

flexible-vlan-tagging;
native-vlan-id 150;
encapsulation extended-vlan-bridge;
unit 0 {
    family ethernet-switching {
        storm-control default;
    }
}
unit 3251 {
    vlan-id 3251;
    input-vlan-map swap;
    output-vlan-map swap;
}

Do I miss something about QinQ or anything else?

Best Answer

The issue is flexible-vlan-tagging is enabled on the port so each logical interface expects a VLAN ID. In your case unit 0 is created without a VLAN specified for that logical unit.

The logical interface on which untagged packets are to be received must be configured with the same native VLAN ID as that configured on the physical interface. To configure the logical interface, include the vlan-id statement (matching the native-vlan-id statement on the physical interface) at the [edit interfaces interface-name unit logical-unit-number] hierarchy level.

https://www.juniper.net/documentation/en_US/junos/topics/task/configuration/interfaces-enabling-vlan-tagging.html

Regarding Path MTU Discovery

Ideally i would be relying on Path MTU discovery. But since the ethernet packets being generated are too large for any other machine to receive, there is no opportunity for IP Packet too big fragmentation messages to be returned

Based on your diagram, I agree that PMTUD cannot function between two different PCs in the same LAN segment; PCs do not generate ICMP Error messages required by PMTUD.

Jumbo frames

Some vendors (such as Cisco) have switch models which support ethernet payloads larger than 1500 bytes. Officially IEEE does not endorse this configuration, but the industry has valid needs to judiciously deviate from the original 1500 byte MTU. I have storage LAN / backup networks which leverage jumbo frame for good reason; however, I made sure that all MTUs matched inside the same vlan when I deployed jumbo frames.

Mismatched MTUs within a broadcast domain

The bottom line is that you should never have mismatched ethernet MTUs inside the same ethernet broadcast domain; if you do, it's a bug or configuration error. Regardless of bug or error, you have to solve these problems, sometimes manually.

All that discussion leads to the next question...

Why is there a spec that intentionally creates invalid ethernet frames?

I'm not sure that I agree... I don't see how the IEEE 802.3 series, or RFC 894 create invalid frames. Host implementations or host misconfigurations create invalid frames. To understand whether your implementation is following the spec, we need a lot more evidence...

This diagram is at least prima facie evidence that your MTUs are mismatched inside a broadcast domain...

+------------------+      +----------------+     +------------------+
| Realtek PCIe GBe |      | NetGear 10/100 |     | Realtek 10/100   |
|       (on-board) |      |     Switch     |     |     (on-board)   |
|                  |      +----------------+     |                  |
| Windows 7        |           ^    ^            |                  |
|                  |           |    |            |                  |
| 192.168.1.98/24  |-----------+    +------------| 192.168.1.10/24  |
| MTU = 1504 bytes |                             | MTU = 1500 bytes |
+------------------+                             +------------------+

How should an 802.3-compliant implementation respond to MTU mismatches?

What was it they [the writers of 'the spec'] expected people to do with devices that generate these too large packets?

MTU 1504 and MTU 1500 within the same broadcast domain is simply a misconfiguration; it should never be expected to work any more than mismatched IP netmasks, or mismatched IP subnets can be expected to work. Your company will have to knuckle-down and fix the root-cause of the MTU mismatches... at this time it's hard to say whether the root cause is user error, an implementation bug, or some combination of the above.

If the affected Windows machines are successfully logging into to an Active Directory Domain, one could write Windows login scripts to automatically fix MTU issues based on some well-constructed tests inside the domain login scripts (assuming the Domain Controller isn't part of the MTU issues).

If the machines are not logging into a domain, manual labor is another option.

Other possibilities to contain the damage

Use a layer3 switch^{Note 1} to build a custom vlan for anything that has broken MTUs and set the layer3 switch's ethernet MTU to match the broken machines; this relies on PMTUD to resolve MTU issues at the IP layer. Layer3 switches generate the ICMP errors required by PMTUD.

This option works best if you can re-address the broken machines with DHCP; and you can identify the broken machines by mac-address.

... why did they bump it up to 1504 bytes, and create invalid packets, in the first place?

Hard to say at this point

802.1ad vs 802.1q

How is IEEE 802.1ad (aka VLAN Tagging, QinQ) valid, when the packets are too large?

I haven't seen evidence so far that you're using QinQ; from the limited evidence I have seen so far, you're using simple 802.1q encapsulation, which should work correctly in Windows, assuming the NIC driver supports 802.1q encap.

End Notes:

^{Note 1}_{Any layer 3 switch should do... Cisco, Juniper, and Brocades all could perform this kind of function.}

Juniper Router – How to Bridge Two QinQ Interfaces

One way you could do this:

Given the following two interfaces:

interfaces {
    ge-1/0/1 {
        flexible-vlan-tagging;
        encapsulation flexible-ethernet-services;
        unit 1 {
            encapsulation vlan-bridge;
            vlan-tags outer 1 inner 600;
        }
    }
    ge-1/0/2 {
        flexible-vlan-tagging;
        encapsulation flexible-ethernet-services;
        unit 1 {
            encapsulation vlan-bridge;
            vlan-tags outer 336 inner 600;
        }
    }

Then normalise at your bridge-domain by specifying vlan-id "none":

bridge-domains {
    QT {
        vlan-id none;
        interface ge-1/0/1.1;
        interface ge-1/0/2.1;
    }
}

You'll then see when you look at your interfaces that the MX will pop both tags on ingress, and then push two new ones to match the egress interface eg:

Logical interface ge-1/0/1.1 (Index 345) (SNMP ifIndex 538)
 Flags: Device-Down SNMP-Traps 0x0
 VLAN-Tag [ 0x8100.1 0x8100.600 ] In(pop-pop) Out(push-push 0x8100.1 0x8100.600) <--
 Encapsulation: VLAN-Bridge
 Input packets : 0
 Output packets: 0
 Protocol bridge, MTU: 1522
  Flags: Is-Primary

Logical interface ge-1/0/2.1 (Index 346) (SNMP ifIndex 542)
  Flags: Device-Down SNMP-Traps 0x0
  VLAN-Tag [ 0x8100.336 0x8100.600 ] In(pop-pop) Out(push-push 0x8100.336 0x8100.600) <--
  Encapsulation: VLAN-Bridge
  Input packets : 0 
  Output packets: 0
  Protocol bridge, MTU: 1522