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Jon_Macy's avatar
Jon_Macy
Icon for Altostratus rankAltostratus
Feb 08, 2018

Another Binary Scan Question - Parsing Binary Flag Fields

Hi All On an LTM only license (so no DNS:: objects which would be much easier I agree, but $$$) I'm trying to parse flag field values out of a DNS UDP Message packet. The packet layout and what I've...
application delivery
LTM
Stanislas_Piro2's avatar
Stanislas_Piro2
Icon for Cumulonimbus rankCumulonimbus
Feb 08, 2018

you can find this irule which decode dns question and encode answer.

First extract flags to bits string

binary scan [UDP::payload] SB16SSSSH* ID REQUEST_FLAGS QDCOUNT ANCOUNT NSCOUNT ARCOUNT RESOURCES

then extract bits from flags

set bit7 [string index $REQUEST_FLAGS 7]

I had the same question and it seems that b option in binary scan read the last bit of the whole byte.