Thanks for reading the articles - it's great to hear that my efforts are helping
others. I'm doing a blog at Infoblox.com, which acquired Netcordia last year:
http://www.netcordia.com/community/blogs/
I try to do a post three times a month, based on the consulting work that we're
doing at Netcraftsmen, where I'm now working. There are some other great blogs
and technical articles on the Netcraftsmen web site (http://netcraftsmen.net,
under Resources), including Pete Welcher (network design), Carole Warner Reece
(variety of topics), Bill Bell (Unified Communications), and others on the
Netcraftsmen team.
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.
Take care!
-tcs
On 4/12/11 9:36 PM, marc abel wrote:
Hey Terry, great to have you posting here. I'm a big fan of a some of
your articles I have come across. Are you writing anywhere regularly?
-Marc
On Tue, Apr 12, 2011 at 8:03 PM, Terry Slattery<[email protected]> wrote:
Steve,
That matches the 10.20.4.0 subnet and 10.30.4.0 subnet, but it won't match
any hosts on either subnet, because the last octet is 0 and the wild-card
bits are zero (must match).
I was looking for a wildcard mask of 0.10.0.255 to match all hosts on either
subnet.
If you went further, you could have also come up with 0.255.0.255, to match
10.x.4.x.
-tcs
On 4/12/11 12:15 AM, Di Bias, Steve wrote:
Terry is right, I may have jumped the gun with the inverse mask statement
(although it's mentioned this way in many documents). For Terry's experiment
let's assume we want to match the voice vlan for buildings 20 and 30
(10.20.4.0 and 10.30.4.0). By breaking this down into binary and using
AND/OR logic we can easily come up with our answer
00001010.00010100.00000100.0000000
00001010.00011110.00000100.0000000
----------------------------------
00001010.00010100.00000100.0000000 = 10.20.4.0
00001010.00010100.00000100.0000000
00001010.00011110.00000100.0000000
----------------------------------
00000000.00001010.00000000.0000000 = 0.10.0.0
So the "wildcard" mask to match both buildings would be 0.10.0.0
Cheers!
Thank you.
Steve Di Bias
Network Engineer - Information Systems
Valley Health System - Las Vegas
Office - 702- 369-7594
Cell - 702-241-1801
[email protected]
-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of Terry Slattery
Sent: Monday, April 11, 2011 6:58 PM
To: Jay Taylor
Cc:<[email protected]>
Subject: Re: [OSL | CCIE_RS] offset-list and wild card mask
Good answer, Jay. For everyone who thinks that the wild-card mask is the
opposite of the subnet mask...
I have a set of subnets that I need to match. The first octet is 10. The
second octet is a building number. The third octet identifies the subnet in
each building, and is "4" for the voice subnet, which is what I want to
match.
Build a wild-card mask that matches
10.x.4.x
Is it the inverse of the subnet mask?
-tcs
On 7/22/64 2:59 PM, Jay Taylor wrote:
Offset list is used to increment the metric of certain routes.
In a wildcard mask a binary 0 means the bit must match and a binary 1
means it does not have to match. This is reverse logic compared to a
normal subnet mask. Also, unlike a subnet mask the 1's and 0's do not
need to be contiguous.
On Mon, Apr 11, 2011 at 11:04 AM, Uli<[email protected]> wrote:
Hi Expert,
Does anyone can explain to me about offset-list as I kind of confused
with it. also, in my opinion that wild card mask is reverse of subnet
mask, but someone told me it isn't ?
Regards
_______________________________________________
For more information regarding industry leading CCIE Lab training,
please visit www.ipexpert.com
--
Terry Slattery CCIE# 1026
_______________________________________________
For more information regarding industry leading CCIE Lab training, please
visit www.ipexpert.com
--
Terry Slattery CCIE# 1026
_______________________________________________
For more information regarding industry leading CCIE Lab training, please visit
www.ipexpert.com
