Wednesday , April 25 2018
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QinQ termination on subinterfaces to support DHCP Relay

So far you have learned basic and selective QinQ on Huawei swiches. They seem like a simple Layer 2 VPN solution, which we can use to connect 2 or more offices. And of course, it is truth.

But, sometimes, we want to have an access to external services or just to the Internet, instead of connecting 2 branch offices. And, still we can use QinQ technology, why not?

The only thing we should do is to terminate QinQ VLAN Tag on a router. Just create L3 subinterface and let the router to use IP routing table to forward packets.

In our LAB, I am going to show you how to terminate QinQ to use DHCP server, located outside our network. In this case DHCP Relay feature must be used.

So let’s get to the point!

QinQ termination on subinterfaces to support DHCP Relay on Huawei

Topology of QinQ to support DHCP Relay

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selective QinQ on Huawei switches

Let’s go ahead with QinQ technology. In the last post you had the opportunity to know basic QinQ tunneling on Huawei switches. The QinQ tunnel attaches the same outer tag to all the frames entering the Layer 2 QinQ interface.

In this lab I would like to attach different outer tags, to the frames entering the Layer 2 QinQ interface, according to different inner tags. It is useful when packets are going to be differentiated in a provider’s network. Why? Because of service type, user’s application etc.

In this case we have 1 enterprise network with branch office located in another city. Customer network is divided into 2 VLANs to differentiate existing services. Our task is to transparently transmit packets, through ISP network, paying attantion to not allowing traffic between VLAN10 and VLAN20.

Selective QinQ topology

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basic QinQ configuration on Huawei switches

In traditional 802.1Q protocol, service provider should assign different VLAN IDs to users of different VLANs. The numer of VLANs is limited to 4094 IDs. In addition, different users cannot use the same VLAN ID.

A simple method to solve this is to implement QinQ. The QinQ technology improves the utilization of VLANs by adding another 802.1Q tag to a packet with an 802.1Q tag. In this manner, services from the private VLAN can be transparently transmitted through the public network. The ISP network only provides one VLAN ID for different VLANs from the same user network. This saves VLAN IDs of an ISP. Meanwhile, the QinQ provides a simple Layer 2 VPN solution to a small MAN or a local area networks.

QinQ tunneling on Huawei switches

Let’s assume that we have two enteprise networks. Each enterprise has two branch offices, located in different cities. As an ISP, we cannot force these enterprises to use different VLAN planning. In our case, both use VLAN 10 and our task is to transparently transmitt traffic, through ISP network, between remote offices.

What we want to achieve is to ensure communication between remote offices of each enterprise and to block communication between Enterprise_1 and Enterprise_2. We can use basic QinQ tunneling in this case. It adds the same outer VLAN tag to all the frames entering a Layer 2 port.

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port security on Huawei switches

How to prevent unauthorized users from connecting their PCs to an enterprise network? How to prevent employees from connecting unauthorized devices to a LAN or moving their computers without permission?

Port Security is a Layer 2 feature, which can be enabled on an interface, to prevent devices with untrusted MAC address, from accessing a switch interface. When enabled, MAC address of the device connected to the port, is dynamically learned by the switch and stored in a memory (by default it is not aged out). Only this MAC address is then allowed to forward traffic over switch port (only one trusted MAC is allowed by default). Every different MAC address will cause the port to go into one of the following states:

  • Protect – packets coming from untrusted MAC address will be dropped,
  • Restrict – packets coming from untrusted MAC address will be dropped and SNMP trap message will be generated (default behavior),
  • Shutdown – port will be put into shutdown state.

Let’s configure  port security feature on a switch port and see, how it works.

<labnarioSW1>sys
Enter system view, return user view with Ctrl+Z.
[labnarioSW1]interface gi0/0/1
[labnarioSW1-GigabitEthernet0/0/1]port link-type access
[labnarioSW1-GigabitEthernet0/0/1]port-security enable

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Link Flapping Protection on Huawei switches

I have come across link flapping protection feature recently. It is available on S5700 switches. It looks like it is a new feature on Huawei switches. I had not met it in older hardware versions. That’s why I decided to write a few words about it. Unfortunatelly, although this command is available in Huawei network simulator eNSP, it does not work properly. But maybe you will have possibility check it on your real devices.

Port flapping (port going UP and DOWN continually) can be caused by a faulty cable, link failure, active/standby switchover, port hardware failure, etc. Frequent status changes on an interface can lead to:

  • STP topology recalculation and changes,
  • ARP entries updates,
  • dynamic routing instability and convergence problems.

All these issues can negatively affect switch performance and should be avoided.

Link Flapping Protection is a feature that can be implemented on an interface to solve problems caused by the flapping port or link. It checks the interface flapping frequency and link flapping detection interval. If the number of interface flapping times reaches the limit, in a specified period, the interface is shut down.

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