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Forum Replies

  1. Hi Thomas,

    1. Sending a RA when using DHCPv6 might sound redundant. You have to keep in mind that the RA is not only used for autoconfiguration. IPv4 uses the subnet mask to check if a destination is inside or outside the subnet. When the destination is outside of the subnet, we'll use the default gateway. In IPv6 we can use the RA to advertise which prefixes are "on link" or "off link". The no-autoconfig flag informs the host to use DHCP instead of autoconfiguration for its IPv6 address.

    2. The hosts will use EUI-64 to configure the 64 bits of address. This should be fine, you can always use DNS registration so that you can reach your hosts with hostnames instead of the IPv6 addresses.

    3. There's a lot of stuff, let's see what the ND/RA options are:

    R1(config-if)#ipv6 nd prefix 2001:1111:1111:1111::/64 14400 14400 ?
    no-autoconfig Do not use prefix for autoconfiguration
    no-onlink Do not use prefix for onlink determination
    no-rtr-address Do not send full router address in prefix advert
    off-link Prefix is offlink

    R1(config-if)#ipv6 nd ?
    advertisement-interval Send an advertisement interval option in RA's
    autoconfig Automatic Configuration
    cache Cache entry
    dad Duplicate Address Detection
    managed-config-flag Hosts should use DHCP for address config
    ns-interval Set advertised NS retransmission interval
    nud Neighbor Unreachability Detection
    other-config-flag Hosts should use DHCP for non-address config
    prefix Configure IPv6 Routing Prefix Advertisement
    ra Router Advertisement control
    reachable-time Set advertised reachability time
    router-preference Set default router preference value
    secured Configure SEND

    no-onlink / off-link: this tells the host if a prefix is on-link or off-link. I'll have to think of some examples when and why we want to use this...something for another tutorial.

    no-rtr-address: this removes the router address so the hosts don't have a default gateway, useful if hosts have to remain in their own subnet.

    managed-config-flag: we've seen this one, it's for DHCPv6.

    other-config-flag: this is for stateless DHCPv6.

    nud: neighbor unreachability detection...no idea how it works, need to lab it up :slight_smile:

    router-preference: useful when you have multiple routers, you can use it to tell hosts what default gateway to prefer.

    secured: haven't tried this before but it's a secure version of NDP (Neighbor Discovery).


  2. I managed to get this lab to work correctly with GNS3 1.5.2 and below IOS´s

    BOOTLDR: 7200 Software (C7200-ADVIPSERVICESK9-M), Version 15.2(4)S5, RELEASE SOFTWARE (fc1)

    BOOTLDR: 7200 Software (C7200-ADVENTERPRISEK9-M), Version 12.4(24)T5, RELEASE SOFTWARE (fc3)

    BOOTLDR: 7200 Software (C7200-ADVIPSERVICESK9-M), Version 15.2(4)S5, RELEASE SOFTWARE (fc1)

  3. Thank you Very Much Rene for your lessons.

    One small configuration problem which I am facing in the IOU with ios 15.0 is as below, while trying to configure the stateful dhcp.

    Router(config)#ipv6 dhcp pool STF
    IPv6 DHCP configuration commands:
      default                              Set a command to its defaults
      dns-server                       DNS servers
      domain-name                Domain name to complete unqualified host names
      exit                                     Exit from DHCPv6 configuration mode
      no                                       Negate a command or set its defaults
      prefix-delegation          IPv6 prefix delegation
      sip                                      SIP Servers options

    The option of configuring "address prefix" after configuring "ipv6 dhcp pool STF" do not appear. Is this a problem with IOU or am I missing some other configurations, which may be done prior to this. I am facing similar problem while trying to configure some of the other features also. May you be able to help me....

  4. Hello Abey.

    Others have had similar problems. It all depends on the version of IOS you're using and the platform. Take a look at this post which includes some IOS versions and platforms on which it has been successfully implemented.

    However, using your version it is possible to implement the same thing using the prefix-delegation command. If you're interested, you can find out more information about that here.

    I hope this has been helpful!


  5. Thank you Laz. Your reply is most appreciated. Have a Great Day !!

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