Difference between revisions of "Cisco IOS Wildcard mask"
m (Created page with "Terry Slattery CCIE#1026 (The fist one to pass a CCIE exam)<ref>http://bigevilsciscoworld.wordpress.com/2011/04/16/wildcard-mask-how-and-why/</ref>: "I had to jump in on the wild...") |
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| − | Terry Slattery CCIE#1026 (The fist one to pass a CCIE exam)<ref>http://bigevilsciscoworld.wordpress.com/2011/04/16/wildcard-mask-how-and-why/</ref>: | + | Terry Slattery CCIE#1026 (The fist one to pass a CCIE exam)<ref>http://bigevilsciscoworld.wordpress.com/2011/04/16/wildcard-mask-how-and-why/</ref>:<br/> |
"I had to jump in on the wildcard mask topic, because the idea of inverting the subnet mask has been around since the early days of Cisco training. I asked Kirk Lougheed, one of Cisco’s founders and the principal software developer at the begining, about why the wildcard mask uses the bits it does (i.e. 1 = don’t care). He told me that it was just a decision he made one day and that it could have gone either way." | "I had to jump in on the wildcard mask topic, because the idea of inverting the subnet mask has been around since the early days of Cisco training. I asked Kirk Lougheed, one of Cisco’s founders and the principal software developer at the begining, about why the wildcard mask uses the bits it does (i.e. 1 = don’t care). He told me that it was just a decision he made one day and that it could have gone either way." | ||
| − | + | <br/><br/> | |
| + | Scott Morris<ref>https://learningnetwork.cisco.com/thread/3194</ref>:<br/> | ||
| + | Access Lists actually came before subnet masks. Remember way back when we lived in an evil classful world. So back in like 1985, when access-lists came about it was actually easier to code in assembler to do a NAND operation instead of an AND. Thus the wildcarding. | ||
| + | <br/><br/> | ||
| + | Francois Labreque<ref>http://www.velocityreviews.com/forums/t297267-why-does-ospf-use-wildcard-mask-bit.html</ref>:<br/> | ||
| + | Access-lists and ospf areas use wildcard masks because back in the days of the AGSes, every CPU cycle counted and using a wilcard mask makes the logic of deciding if a packet matches a couple of cpu cycles faster. | ||
==References== | ==References== | ||
<references/> | <references/> | ||
Latest revision as of 15:13, 5 September 2012
Terry Slattery CCIE#1026 (The fist one to pass a CCIE exam)[1]:
"I had to jump in on the wildcard mask topic, because the idea of inverting the subnet mask has been around since the early days of Cisco training. I asked Kirk Lougheed, one of Cisco’s founders and the principal software developer at the begining, about why the wildcard mask uses the bits it does (i.e. 1 = don’t care). He told me that it was just a decision he made one day and that it could have gone either way."
Scott Morris[2]:
Access Lists actually came before subnet masks. Remember way back when we lived in an evil classful world. So back in like 1985, when access-lists came about it was actually easier to code in assembler to do a NAND operation instead of an AND. Thus the wildcarding.
Francois Labreque[3]:
Access-lists and ospf areas use wildcard masks because back in the days of the AGSes, every CPU cycle counted and using a wilcard mask makes the logic of deciding if a packet matches a couple of cpu cycles faster.