VoIP-X technical specification

The VoIP-X network is set up according to regulation ILR/T17/9, option 2.2, Layer 2 interconnection, with the exception that a single VLAN is made available to all participants, and that any SIP traffic between participants resides in this same VLAN.

LU-CIX makes available a transparent Layer 2 interconnect between participants, making available a certain number of QoS traffic classes with corresponding treatment, and bears no responsibility for the exchange of SIP messages and RTP media traffic, or the compatibility between participant’s systems.


Ports, IPv4 and IPv6

All ports on the LU-CIX VoIP-X infrastructure are Ethernet and are available at the following speeds:

  • 10 Gbps (10GE) - 10GBASE-LR
  • 100 Gbps (100GE) – 100GBASE-LR4 (100GBASE-LR1 on special request)

Additionally, LU-CIX is able to aggregate 10GE ports to provide higher bandwidth trunks.

VoIP-X ports can be shared with other services, or can be dedicated. In both cases, the VoIP-X service is made available on a dedicated VLAN, i.e. ports must be configured as trunk ports.

Each participant must respect the security requirements of ILR/T17/9 chapter 2.4. LU-CIX assigns 1 public IPv4 and 1 public IPv6 address per port per participant. The IP addresses must not be announced to the Internet by any participant, and will not be anounced by LU-CIX. Participants are limited to a single MAC address per port, which is enforced by the LU-CIX network.

Participants would typically announce a minimal set of prefixes via BGP such that the IP range of their SIP endpoints is reachable by the other participants. BGP sessions must be established individually with each participant with whom SIP traffic is to be exchanged.

A participant could also run SIP services on his assigned VoIP-X IP address. In this case, additional setup is required by this participant in order to establish connectivity to participants who locate the SIP endpoints within their network.


MAC Layer

Ethernet framing

The LU-CIX VoIP-X infrastructure is based on the Ethernet II (or “DIX Ethernet”) standard. This means that LLC/SNAP encapsulation (802.2) is not permitted.


Frames forwarded to VoIP-X ports must have one of the following Ether types:

  • 0x0800 - IPv4
  • 0x0806 - ARP
  • 0x86dd - IPv6

One MAC address per port

Frames forwarded to an individual LU-CIX port must all have the same source MAC address. LU-CIX enforces the single MAC address per port by using Port Security and MAC filtering. For security reasons, reception of a frame with any other source MAC address will trigger an automatic port shutdown.

Hardware changes also introduce a change of the source MAC address. To guarantee a smooth migration please contact LU-CIX support (support@lu-cix.lu) a few business days ahead of your change. During a short period of time we can accept two different source MAC addresses on a port.


Network layer

No proxy ARP

Use of proxy ARP on the router's interface to the Exchange is not allowed.

Unicast only

Frames forwarded to LU-CIX ports must not be addressed to a multicast or broadcast MAC destination address except as follows:

  • Broadcast ARP packets.
  • Multicast ICMPv6 Neighbour Discovery packets. This DOES NOT include Router Discovery packets.

No link-local traffic

Traffic for link-local protocols shall not be forwarded to LU-CIX ports.
Link-local protocols include, but are not limited to, the following list:

  • IRDP
  • ICMP redirects
  • IEEE 802 Spanning Tree
  • Vendor proprietary protocols. These include, but are not limited to:
    • Discovery protocols: CDP, EDP
    • VLAN/trunking protocols: VTP, DTP
    • Interior routing protocol broadcasts (e.g. OSPF, ISIS, IGRP, EIGRP)
  • PIM-SM
  • PIM-DM
  • ICMPv6 ND-RA
  • UDLD
  • L2 Keepalives

The following link-local protocols are exceptions and are allowed:

  • ARP
  • IPv6 ND

No directed broadcast

IP packets addressed to the VoIP-X directed broadcast address must be blocked by the member.

Only SIP-related traffic allowed

Other than the protocols required for network operations, the only traffic allowed on the VoIP-X network is SIP and RTP. If participants want to exchange other types of Internet related IP traffic, they must use the LU-CIX Peering network.

Quality of Servcice (QoS)

QoS is a required element of a network forwarding voice traffic. LU-CIX aligns the QoS configuration on regulation ILR/T17/9, chapter 2.5 and makes available the following traffic classes:

Traffic typeTraffic classDSCPIP Precedence
Voice and SigVoiceExpedited Forwarding (EF)465
Network controlClass Selector 6 (CS6)486
Best EffortDefault Forwarding (DF)00


Participants MUST mark their traffic according to above DSCP and/or IP Precedence. Traffic not marked by the participant is automatically assigned to the Best Effort class.

Any QoS marking applied by participants is transported unaltered over VoIP-X.

BFD (Bidirectional Forwarding Detection)

In case a participant is connected in a redundant fashion to the VoIP-X network, we recommend setting up BFD in parallel to BGP, in order to have a fast failure detection and to minimise the impact on voice services.