Thanks Anthony!
I should have included that I would be looking at ACLs only, nothing
like modifying router interfaces or anything like. Using DHCP reserved
addresses, the clients in question would get the appropriate IP
address and be allowed through.
---
Lelio Fulgenzi, B.A.
Senior Analyst, Network Infrastructure
Computing and Communications Services (CCS)
University of Guelph
519‐824‐4120 Ext 56354
[email protected]
www.uoguelph.ca/ccs
Room 037, Animal Science and Nutrition Building
Guelph, Ontario, N1G 2W1
-------------------------
FROM: "Anthony Holloway" <[email protected]>
TO: "Lelio Fulgenzi" <[email protected]>, "Cisco-voip
([email protected])" <[email protected]>
SENT: Thursday, February 5, 2015 11:29:24 AM
SUBJECT: Re: [cisco-voip] OT: using subnet/wildcard mask for group
within a group, issues?
I'm no Route/Switch engineer, so I'm likely wrong here, but I'll give
my two cents anyway.
You didn't specifically state what you are doing though. E.g., ACLs,
Interfaces, Routes, etc.
Let's pretend for a moment you wanted to carve out a new network in
your environment for this range.
I don't think you'll be allowed to configure this as different
interfaces within a single router. It will tell you that the address
on the interface is overlapping with another interface, or something
like that. With that, what you could do, is redesign your subnets for
this range. You will need to go through the exercise of changing all
of the subnet masks for the hosts between .1 - .54. However, it's
likely not going to be that easy, as you can see below, the new
variable length subnet masks will chop up your existing network into
four new networks. The fourth and last one is your desired new
network, so really you end up with three networks for the 50 potential
hosts which exist in that lower range.
Current (host range) [count]:
192.168.45.0/26 [1] (.1 - .62) [62]
New (host range) [count]:
192.168.45.0/27 [6] (.1 - .30) [30] *
192.168.45.32/28 [7] (.33 - .46) [14] **
192.168.45.48/29 [8] (.49 - .54) [6] ***
192.168.45.56/29 [2] (.57 - .62) [6]
*Because of the new broadcast address of .31, you'd have to re-ip the
current .31 host
**Because of the new network address of .32, you'd have to re-ip the
current .32 host. Same for the broadcast address of .47, you'd have to
re-ip the current .47 host
***Because of the new network address of .48, you'd have to re-ip the
current .48 host. Same for the broadcast address of .55, you'd have to
re-ip the current .55 host
To see this visually:
If you did a router on a stick with sub interfaces for the four new
subnets, then the hosts communicating between subnets cannot talk at
layer 2 anymore, and would need to be routed. If you had them plugged
into a layer 3 switch that was doing routing, then I wouldn't suspect
much would change in terms of traffic patterns or network load. This
would be further reduced if you addressed common servers contiguously.
E.g., CUCM+CUC+CER+IM&P as .5, .6, .7, and .8.
Routes to this router would not have to change, which is nice, but
that's only if your routes were nicely summarized to begin with. I
suspect they are. E.g,, A route of 192.168.45.0/26 [1] going to this
router, which now has four sub interfaces, one for each new subnet,
would still work fine, and would not need to change. If I'm not
mistaken, some/all routing protocols would summarize these four
networks into 192.168.45.0/26 [1] anyway, for the purpose of
advertising to other routers. You may have to turn on route
summarization however.
Now, let's pretend you actually just wanted to create an ACL to permit
those last 6 hosts to access some other subnet, and keep your existing
network intact. Then, this is a whole lot less work and you simply
need to create an ACE for your ACL which permits the wild card match.
Let's assume that your protected voice subnet was 192.168.46.0/26 [9]
permit ip 192.168.45.56 0.0.0.7 192.168.46.0 0.0.0.63
Or if not using wild card masks
permit ip 192.168.45.56 255.255.255.248 192.168.46.0 255.255.255.192
I don't know if that helped or not, but it was fun using subnet
calculating again. Something I haven't done in quite a few years. I
think I did it right. ;)
On Thu Feb 05 2015 at 9:11:18 AM Lelio Fulgenzi <[email protected]>
wrote:
This group is full of it. Knowledge, that is. So who better to ask
these questions....
I've got a subnet, say 192.168.45.0/26 [1], of which I want to allow
only a small group of that subnet to access a particular host. I'm
able to reserve the top end, which falls into another subnet,
192.168.45.56/29 [2].
So, the first network, 192.168.45.0 has network id .0, first host
.1, last host .62, b/cast .63
And, the subgroup would be, network id .56, first host .57, last
host .62, b/cast .63
I'm thinking, as long as I don't use 56 and 63, I can do this.
The hosts I will be protecting will be voice gateways, and
collaboration servers, e.g. callmanager, connection, etc.
Would there be a time where the hosts being protected would
interpret the incorrect broadcast address? I don't see how. But I
could be missing something.
Lelio
---
Lelio Fulgenzi, B.A.
Senior Analyst, Network Infrastructure
Computing and Communications Services (CCS)
University of Guelph
519‐824‐4120 Ext 56354 [3]
[email protected]
www.uoguelph.ca/ccs [4]
Room 037, Animal Science and Nutrition Building
Guelph, Ontario, N1G 2W1
_______________________________________________
cisco-voip mailing list
[email protected]
https://puck.nether.net/mailman/listinfo/cisco-voip [5]
Links:
------
[1] http://192.168.45.0/26
[2] http://192.168.45.56/29
[3] tel:519%E2%80%90824%E2%80%904120%20Ext%2056354
[4] http://www.uoguelph.ca/ccs
[5] https://puck.nether.net/mailman/listinfo/cisco-voip
[6] http://192.168.45.0/27
[7] http://192.168.45.32/28
[8] http://192.168.45.48/29
[9] http://192.168.46.0/26
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