nanog mailing list archives
Re: Stupid Question maybe?
From: William Herrin <bill () herrin us>
Date: Wed, 19 Dec 2018 12:28:36 -0800
On Wed, Dec 19, 2018 at 12:12 PM Thomas Bellman <bellman () nsc liu se> wrote:
On 2018-12-19 20:47 MET, valdis.kletnieks () vt edu wrote:There was indeed a fairly long stretch of time (until the CIDR RFC came out and specifically said it wasn't at all canon) where we didn't have an RFC that specifically said that netmask bits had to be contiguous.How did routers select the best (most specific) route for an address? If the routing table held both (e.g.) 10.20.30.0/255.255.255.64 and 10.20.30.0/255.255.255.32, then 10.20.30.97 would match both, and have the same number of matching bits.
Easy: .97 matches neither one because 64 & 97 !=0 and 32 & 97 != 0. That's a 0 that has to match at the end of the 10.20.30. The problem is 10.20.30.1 matches both, so which one takes precedence? Can't have a most-specific match when two matching routes have the same specificity. I'm guessing the answer was: the routing protocols didn't accept netmasks in the first place and you were a fool to intentionally create overlapping static routes. Regards, Bill -- William Herrin ................ herrin () dirtside com bill () herrin us Dirtside Systems ......... Web: <http://www.dirtside.com/>
Current thread:
- Re: Stupid Question maybe?, (continued)
- Re: Stupid Question maybe? Saku Ytti (Dec 20)
- Re: Stupid Question maybe? Grant Taylor via NANOG (Dec 20)
- Re: Stupid Question maybe? Saku Ytti (Dec 20)
- RE: Stupid Question maybe? Naslund, Steve (Dec 19)
- Re: Stupid Question maybe? Patrick W. Gilmore (Dec 19)
- RE: Stupid Question maybe? Naslund, Steve (Dec 19)
- Re: Stupid Question maybe? Adam Atkinson (Dec 20)
- Re: Stupid Question maybe? Smoot Carl-Mitchell (Dec 20)
- Re: Stupid Question maybe? valdis . kletnieks (Dec 19)
- Re: Stupid Question maybe? Thomas Bellman (Dec 19)
- Re: Stupid Question maybe? William Herrin (Dec 19)
- Re: Stupid Question maybe? Thomas Bellman (Dec 19)
- Re: Stupid Question maybe? Owen DeLong (Dec 19)
- RE: Stupid Question maybe? David Edelman (Dec 19)
- Re: Stupid Question maybe? Baldur Norddahl (Dec 19)
- Re: Stupid Question maybe? Joe (Dec 19)
- Re: Stupid Question maybe? valdis . kletnieks (Dec 19)
- Re: Stupid Question maybe? William Allen Simpson (Dec 20)
- Re: Stupid Question maybe? Saku Ytti (Dec 20)
- Re: Stupid Question maybe? Joel Halpern (Dec 20)
- Re: Stupid Question maybe? Tony Finch (Dec 24)