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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VPN FRR on Huawei routers

Last time IP FRR on Huawei routers was introduced. Let’s go on with VPN FRR today.

VPN FRR topology

  1. Configure IP addresses based on the topology (omitted)
  2. Configure ISIS on PE1, PE2 and PE3.
  3. Configure MPLS function on all PE routers and enable MPLS LDP to set up an LSP.
  4. Configure VPN instance on all PE devices.
  5. Configure MP-IBGP between PE routers.
  6. Configure EBGP between CE and PE2/PE3 routers.
  7. Configure VPN FRR policy on PE1.
  8. Configure BFD session between PE1 and PE2.

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L2TP LAC-auto-initiated tunnel mode

 Layer 2 tunneling protocol (L2TP) connection can be established in the following tree modes:

  • NAS-initializated
  • Client-initializated
  • LAC-auto-initializated.

This is not my job to tell you about the theory. You can find plenty of information about L2TP on the internet. Let’s focus today on the third mode.

In most cases, an L2TP user directly dials up to a LAC, and only connection is established between the user and LAC. Unlike NAS and Client-initializated modes, in LAC-auto-initializated mode users can connect to the LAC by sending IP packets. At the same time LAC needs to have a PPP user created and a tunnel with the LNS established. The two ends of an L2TP tunnel reside on LAC and LNS respectively. As you can see from the topology below, in LAC-auto-initiated mode, LAN can be directly connected to LAC.

L2TP topology

Let’s look how to configure L2TP on Huawei routers.

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