Since I didn't know where to post this question I'm psoting it here under Security:
In my effort to verify the integrity of binary data as stored on Cisco devices or stored on file servers, I ran across some checksums, which I'm unable to find information about.
1.) router checksum
When downloading an IOS image with a CCO account the following information is given:
BSD Checksum -
Router Checksum 0x415c
Date Published: 25-JUL-2007
I do understand MD5 checksums and how to use them, however I have no clue what the router checksum is and how to use or to verify it. Any ideas where to find this checksum to verify it against? Or any idea on the algorithm used to compute this checksum?
BTW why is the BSD checksum not computed here? What would be the algorithm for the BSD checksum?
2.) CCO checksum
At each Cisco device the 'verify' command can be used to generate checsums:
In the new UDP header, the checksum value is always assigned to zero. This value prevents an intermediate device from validating the checksum against the packet checksum, thereby, resolving the TCP UDP checksum issue because NAT changes the IP source and destination addresses
Table of ContentsIntroductionVersion HistoryPossible Future
UpdatesDocuments PurposeNAT Operation in ASA 8.3+ SectionsRule Types
Network Object NATTwice NAT / Manual NATRule Types used per SectionNAT
Types used with Twice NAT / Manual NAT and Network Obje...
Table of Contents Introduction:This document describes details on how
NAT-T works. Background: ESP encrypts all critical information,
encapsulating the entire inner TCP/UDP datagram within an ESP header.
ESP is an IP protocol in the same sense that TCP an...