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Re: Multicast TTL Scoping posted 06/24/2004
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Tom,

YUP!  Admin scoping refers to applying multicast border filters.  The idea
behind RFC 2365 is that the parts of the 239/8 space are reserved for local,
site, organization and global reach.  This attempts to standardize addresses
that should be permitted/denied at various boundaries.



Bob Sinclair
CCIE #10427, CISSP, MCSE
www.netmasterclass.net

  ----- Original Message -----
  From: Tom Rogers
  To: Bob Sinclair ; ccielab@xxxxxxxxxxxxxx
  Sent: Thursday, June 24, 2004 3:43 PM
  Subject: Re: Multicast TTL Scoping


  Bob,
  Thanks.

  When you referred to adminstrative scoping, you meant making a boundary?
  ie deny what you dont want and permit rest by using ip multicast boundary
acl command?

  Tom

  Bob Sinclair <bsinclair@xxxxxxxxxxxxxxxxxx> wrote:
    Tom,

    I believe I can confirm your understanding of TTL scoping. The router
    compares the ttl in the packet to the configured interface ttl threshold.
    The ttl in the packet must exceed the threshold value in order for the
    packet to exit the interface.

    By combining starting ttl values with interface threshold values, you can
    limit the extent of some multicasts while allowing other multicasts (with
    higher starting ttls) to transit.

    Another method of achieving a similar result is "administrative scoping",
    documented in rfc 2365. Rather than relying on ttl, you reserve address
    spaces for different scopes and filter the addresses on the border
    interfaces.

    HTH,

    Bob Sinclair
    CCIE #10427, CISSP, MCSE
    www.netmasterclass.net


    ----- Original Message -----
    From: "Tom Rogers"
    To:
    Sent: Thursday, June 24, 2004 1:48 PM
    Subject: Multicast TTL Scoping


    > Hi group,
    > As far I understand if the inteface is configured for very high ttl on
the
    interface, it will not forward multicast traffic.
    >
    > I have R1----R2----R3 E0--Rest of the network
    >
    > I have RP R1 as ip pim send-rp-discovery + announce with scope 16
    > If I put ip multicast ttl-threhold as 255 on R3 E0, the multicast
traffic
    will not be forwarded to the rest of the network,
    >
    > Am I right here?
    >
    http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122cgcr/f
iprmc_r/mult/1rfmult2.htm#wp1078617
    >
    > Thanx
    > Tom
    >
    >
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