Subject: Re: [pim] PIM-SM RFC4601 Encoding questions

From: "Prashant Jhingran (pjhingra)" <[email-masked]>
Date: Tue, 1 Jul 2008 17:19:26 +0530

Hi James,

Indeed the mask length for the source address is always set to full.
 
IMO...  

*,G joins are basically used to discover possible sources via RPT.
Destination DR (DDR) would ideally switch to SPT the moment it receives
(i.e. discovers) traffic for a "S",G (in which DDR is interested) out of
*,G and would consequently send periodic SG RPT prunes along with *,G
join (once SPT is formed) towards RPF(RP). 

Thus mask length other than full might not be of much use and may also
lead to more processing on upstream RPF(RP)router(s) in terms of
decision making i.e. which all subnets to fwd and which to deny.

Regards,
Prashant Jhingran
www.cisco.com 
Phone:   +91-80-442 61800
 
-----Original Message-----
From: [email-masked] [mailto:[email-masked]] On Behalf Of
James Courtier-Dutton
Sent: Monday, June 30, 2008 5:22 PM
To: [email-masked]
Subject: [pim] PIM-SM RFC4601 Encoding questions

In Section 4.9.1
For: Encoded-Group Address:

Mask Len
        The Mask length field is 8 bits.  The value is the number of
        contiguous one bits that are left justified and used as a mask;
        when combined with the group address, it describes a range of
        groups.  It is less than or equal to the address length in bits
        for the given Address Family and Encoding Type.  If the message
        is sent for a single group, then the Mask length must equal the
        address length in bits for the given Address Family and Encoding
        Type (e.g., 32 for IPv4 native encoding, 128 for IPv6 native
        encoding).

For: Encoded-Source Address

Mask Len
        The mask length field is 8 bits.  The value is the number of
        contiguous one bits left justified used as a mask which,
        combined with the Source Address, describes a source subnet.
        The mask length MUST be equal to the mask length in bits for the
        given Address Family and Encoding Type (32 for IPv4 native and
        128 for IPv6 native).  A router SHOULD ignore any messages
        received with any other mask length.

So, for the Source address, Is the mask essentially not used for masking
at all?

I would have thought that this would have been a useful feature, if one
wanted to join any source on a subnet for a particular group.
Why is it specifically rejected?

James
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---

From: "Prashant Jhingran (pjhingra)" <[email-masked]>
Date: Tue, 1 Jul 2008 17:46:16 +0530

Hi James,

Kindly ignore my previous mail, I misinterpreted your question. 

Regards,
Prashant Jhingran
www.cisco.com 
Phone:   +91-80-442 61800
 
-----Original Message-----
From: [email-masked] [mailto:[email-masked]] On Behalf Of
Prashant Jhingran (pjhingra)
Sent: Tuesday, July 01, 2008 5:19 PM
To: James Courtier-Dutton
Cc: [email-masked]
Subject: Re: [pim] PIM-SM RFC4601 Encoding questions

Hi James,

IMO...  

Regards,
Prashant Jhingran
www.cisco.com 
Phone:   +91-80-442 61800
 
-----Original Message-----

In Section 4.9.1

Mask Len

Mask Len

James