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Snap Internet IPv6 DSL Information

IMPORTANT: This document is being less actively edited as IPv6 support is slowly enhanced by Snap. Although the service has been announced I feel it is more in a 'ready for test' phase for the kind of things I would expect for an IPv6 network.


Snap has announced their IPv6 support for DSL customers. In theory this should 'just work' for all customers, in that snap have enabled IPv6 support for all customers iff their equipment supported ipv6 and is configured in the 'correct' way.  Each customer gets a full /48 prefix.

Address configuration is not working and prefix delegation is performed with dhcp.


  1. Does the DSL hop have a global ipv6 address (it doesn't)
    1. Should an IPv6 address be obtained by auto-configuration? The remote end has an addresses of 2406:e000:98:1::1 (or 2406:e000:97:1::1).
  2. Is the dhcp prefix 'static':
    1. It doesn't appear to be
    2. seems to be for one day
    3. new radius server should address this limitation in the near future
  3. Is reverse DNS supported [no]
    1. Is delegation of the DNS for the ipv6 prefix supported [no]
    2. Does snap provide reverse DNS services [no]
    3. How will reverse dns of the Point-to-point link be handled [unknown]
    4. reverse dns of the snap prefix 2406:e000 is very limited (no routers appear by name in traceroutes)


    The following configuration is required:

    Setting Value
    Encapsulation PPPoA
    The modem must be configuraed for PPoA. A PPPoE configuration doesn't appear to work. The support desk doesn't seem to understand PPPoE at this point in time. The PPPoA support also supports a MTU of 1500, whereas the PPPoE configuration is limited to 1492 (even when  using 'pppoe-client ppp-max-payload 1500')
    VPI/VCI 0/100
     This is the standard setting for BUBA DSL
    IPv6 address
    The interface has a link local address but no global unicast IPv6 address is assigned to the PPP dialer interface.

    : Determine if SLAAC or DHCP is used
    IPv6 prefix
    An IPv6 /48 prefix is provided by DHCP.

    Note: As of August 2011, the prefix is for 1 day (86400 seconds) and changes with each DHCP request.
    DNS Servers

    Manually configured.

    Note: The servers 2406:e000::100, 2406:e000::200, 2406:e000::300 are authoritative servers **AND** recursive caching servers.
    Full size frames (but not jumbo frames). This confirmed in the router advertisement message from Snap.



    The firewall must allow outgoing DHCP requests from the router, and the return traffic from the DHCP server. It is important to note that:

    • the DHCP request is sent to the multicast address FF02::1:2 UDP port 547
    • the DHCP response comes from a link local address on UDP port 547 to port 546



    DHCP v6

    Aug 27 20:36:55.345: IPv6 DHCP: Sending SOLICIT to FF02::1:2 on Dialer0
    Aug 27 20:36:55.373: IPv6 DHCP: Received ADVERTISE from FE80::90:1A00:D7A3:450E on Dialer0
    Aug 27 20:36:55.373: IPv6 DHCP: Adding server FE80::90:1A00:D7A3:450E
    Aug 27 20:36:55.373: IPv6 DHCP: Option RECONF-ACCEPT(20) is not processed
    Aug 27 20:36:55.373: IPv6 DHCP: Sending REQUEST to FF02::1:2 on Dialer0
    Aug 27 20:36:55.377: IPv6 DHCP: DHCPv6 changes state from SOLICIT to REQUEST (ADVERTISE_RECEIVED) on Dialer0
    Aug 27 20:36:55.389: IPv6 DHCP: Received REPLY from FE80::90:1A00:D7A3:450E on Dialer0
    Aug 27 20:36:55.389: IPv6 DHCP: Option RECONF-ACCEPT(20) is not processed
    Aug 27 20:36:55.389: IPv6 DHCP: Processing options
    Aug 27 20:36:55.389: IPv6 DHCP: Adding prefix 2406:E000:6164::/48 to snap
    Aug 27 20:36:55.389: IPv6 DHCP: T1 set to expire in 43200 seconds
    Aug 27 20:36:55.389: IPv6 DHCP: T2 set to expire in 69120 seconds
    Aug 27 20:36:55.389: IPv6 DHCP: DHCPv6 changes state from REQUEST to OPEN (REPLY_RECEIVED) on Dialer0

    IPv6 DHCP lease

    # show ipv6 dhcp in dial 0
    Dialer0 is in client mode
      Prefix State is OPEN
      Renew will be sent in 11:59:50
      Address State is SOLICIT (4)
      Retransmission timer expires in 00:00:04
      List of known servers:
        Reachable via address: FE80::90:1A00:D7A3:450E
        DUID: 000200000A4C453132302F373435414333334558322FD7
        Preference: 0
        Configuration parameters:
          IA PD: IA ID 0x000B0001, T1 43200, T2 69120
            Prefix: 2406:E000:616A::/48
                    preferred lifetime 86400, valid lifetime 86400
                    expires at Aug 28 2011 10:51 PM (86391 seconds)
          Information refresh time: 0
      Prefix name: snap
      Prefix Rapid-Commit: disabled
      Address Rapid-Commit: enabled

    ipv6 routers

    The router advertisement from the Snap router doesn't include an onlink autoconfig prefix.

    # show ipv6 routers
    Router FE80::90:1A00:D7A3:450E on Dialer0, last update 0 min
      Hops 0, Lifetime 1800 sec, AddrFlag=0, OtherFlag=0, MTU=1500
      HomeAgentFlag=0, Preference=Medium
      Reachable time 0 (unspecified), Retransmit time 0 (unspecified)

    dialer interface

    #show ipv6 interface dialer 0
    Dialer0 is up, line protocol is up
      IPv6 is enabled, link-local address is FE80::222:90FF:FE98:E85B
      No Virtual link-local address(es):
      Description: PPPoA to ISP
      Stateless address autoconfig enabled
      No global unicast address is configured
      Joined group address(es):
      MTU is 1500 bytes
      ICMP error messages limited to one every 100 milliseconds
      ICMP redirects are enabled
      ICMP unreachables are sent
      Output features: CCE Classification Zone based Firewall QoS classify QoS actions
      Post_Encap features: QoS Actions
      Service-policy output: QosQueuingPolicy
      ND DAD is enabled, number of DAD attempts: 1
      ND reachable time is 30000 milliseconds (using 30000)
      ND RAs are suppressed (periodic)
      Hosts use stateless autoconfig for addresses.

    Snap name servers

    The snap domain has three authoritative DNS servers. It looks like they are on the same network. It is unclear whether they are recursive caching servers.

    # dig @2406:e000::100 ns
    ; <<>> DiG 9.8.0-P4-RedHat-9.8.0-9.P4.fc15 <<>> @2406:e000::100 ns
    ;; global options: +cmd
    ;; Got answer:
    ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 9051
    ;; flags: qr aa rd; QUERY: 1, ANSWER: 3, AUTHORITY: 0, ADDITIONAL: 6
    ;; WARNING: recursion requested but not available
    ;                   IN      NS
    ;; ANSWER SECTION:            86400   IN      NS            86400   IN      NS            86400   IN      NS
    ;; ADDITIONAL SECTION:        86400   IN      A        86400   IN      AAAA    2406:e000::100        86400   IN      A        300     IN      AAAA    2406:e000::200        86400   IN      A        300     IN      AAAA    2406:e000::300
    ;; Query time: 40 msec
    ;; SERVER: 2406:e000::100#53(2406:e000::100)
    ;; WHEN: Sun Sep 11 18:57:54 2011
    ;; MSG SIZE  rcvd: 215
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