When implementing a PGM client server application we encountered a problem with the way our Cisco router (model 2651) interprets the Option field in the PGM header.
According to the PGM standard (RFC3208) the option field is defined as follows (section 8 page 32):
This field encodes binary indications of the presence and significance of any options. It also directly encodes some options.
bit 0 set => One or more Option Extensions are present
bit 1 set => One or more Options are network-significant
Bits are numbered here from left (0 = MSB) to right (7 = LSB).
To the best of our understanding it follows that to indicate an option is present the value of the option field in the PGM header should be 0x80 and if a network significant option is included the value should be 0xC0.
Our cisco router however expects the option field to be 0x01 for options presents and 0x03 for network significant. That is the router expects the bits to be in revers order.
Obviously when encoding packets with the option field as defined in the RFC standard the router does not process the options. The main problem is that the router does not process NAK lists and hence prevents the receivers from getting repair data. To solve the problem we had to change the bit order in the option field.
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