[Xorp-hackers] doubt abt packet format(PIM)

[Ashish Karpe]

hello,
We want to implement packet header for DF -election messages.The format is
as under:

All DF election BIDIR-PIM control messages share the common header
   below:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |PIM Ver| Type  |Subtype| Rsvd  |           Checksum            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |               RP Address (Encoded-Unicast format)           ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                   Sender Metric Preference                    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Sender Metric                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

The Sub-type field  is to be implemented.But
In pim.h

Struct  pim {
.
.
.
uint8_t   pim_reserved
uint16_t pim_checksum
.
.
.}

we want to add the sub type....how do we add it without disturbing the
already existing code.
Is it possible to add that subtype in this structure or do we have to define
another structure which will be only used for DF election messages.
Also can we use the already defined flag
#define PIM_ALL_DF_ELECTION
in file pim.h. How can we use this flag for bidir DF election messages.

Thanking you in anticipation
ashish karpe
chintamani wandhre
shamita pisal
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