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BT FTTC using AAISP

BT FTTC (Fiber To The Cabinet) is supplied as a VDSL2 service along with a BT branded Huawei VDSL2 modem which presents the service using PPPoE. These are notes about configuring a Mikrotik router to work with the FTTC service from AAISP.

The AAISP Knowledge Base and AAISP Wiki are essential resources and should be checked before doing any configuration changes.

Change Log
09/01/2011	Added notes about native IPv6 and 1500 MTU.

Native IPv6 over PPPoE

Native IPv6 over PPPoE requires RouterOS v5.0 to work. It is currently a release candidate but it has been running without issues here for months now.

AAISP IPv6 KB article should be read for general configuration notes.

The only required configuration is to set the prefix up on your LAN interface or bridge.


      /ipv6 address

      add address=2001:8B0:XXX:1::/64 advertise=yes disabled=no eui-64=yes interface=LAN_Bridge

Replace XXX with your assigned prefix.

Change Log
v1.0	Initial version.

1500 MTU over PPPoE using baby jumbo frames

PPPoE requires an 8 byte header to be added to each packet. This causes the payload to be restricted to a 1492 MTU if the underlying medium is regular Ethernet. The BT VDSL2 modem supports using baby jumbo frames of 1508 bytes so the PPP payload is now 1500 bytes which is the same as regular Ethernet.

A 1500 MTU is important because there are many networks and hosts out on the internet which are poorly configured and block all ICMP packets in an attempt to gain extra security but inadvertently breaking Path MTU Discovery.

Assuming the first Ethernet interface is used for PPPoE:


    /interface ethernet

    set 0 arp=enabled auto-negotiation=yes bandwidth=unlimited/unlimited comment="BT VDSL2 Modem Interface" disabled=no full-duplex=yes l2mtu=1524 \

    mac-address=00:0C:42:59:XX:XX master-port=none mtu=1508 name=WAN speed=100Mbps

    /interface pppoe-client

    add ac-name="" add-default-route=yes allow=chap comment="A&A FTTC" dial-on-demand=no disabled=no interface=WAN max-mru=1500 \

    max-mtu=1500 mrru=disabled name=PPPoE password=xxx profile=pppoe-client-default service-name="" use-peer-dns=no user=xxx@xxx

The LCPFix option needs to be enabled for this FTTC line on the Clueless configuration pages. RouterOS doesn't support RFC4638 so needs this option enabled.

Once all these changes are made and the LCPFix option is enabled, the router should be restarted.

Change Log
v1.0	Initial version.