Subnetting and router ip addresses

Hello all
Can someone tell me if you can have a network of e.g 172.19.55.0 with a mask of 255.255.252.0
Also when subnetting what ip address would you put your router on and what mask, would it have to be in the range you applied and the same mask ?
thanks all

If you have a mask 252, then the corresponding octet must be a multiple of 4 to make a network address. For example 172.19.48.0, 172.19.52.0, 172.19.56.0 etc are all valid subnet addresses.
The address 172.19.55.0 would be seen as a host address within the 172.19.52.0/22 subnet. The subnet goes from 172.19.52.0 to 172.19.55.255, but the first address (172.19.52.0) is the address if the subnet itself, and the last (172.19.55.255) is the directed broadcast address. Anything between is valid as a host address. You can put your router on any of those valid host addresses, as long as you get the mask right.
Kevin Dorrell
Luxembourg

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VLAN subnets and routing

Hi,
A couple of years ago I had a vlan which was something like this 192.168.200.0/22. I'm looking to this again but I want to make it 192.168.0.0/16.
I've forgotten the original setup of this, so.... I'm connecting a router to a swtich. On the router interface I've assigned the IP address 192.168.1.250. If I were connecting a device that was on something like 192.168.100.1, would using 192.168.1.250 be fine as the next hop?
Thanks

I am not quite clear on what you are trying to achieve. But I do have this comment. The Cisco router should accept the configuration of 192.168.1.250 255.255.0.0. But depending on the OS of the connected hosts there may be problems where the OS considers an address in 192.168.x.x to be class C and will not accept a default gateway which it considers to be in a different network. If you were doing this in network 10.0.0.0 it would be safer than doing it in 192.168.
HTH
Rick

Have a 1st generation Apple TV, which is not showing as a device in iTunes. Had no problems with Apple TV until I changed from a Windows PC to an iMac. I have changed my IP address, sub mask address and router address in the Apple TV, Can anyone help?

I have a 1st generation apple TV, which was working perfectly until I changed from a Windows PC to a Imac. The Apple TV will not show in Itunes. I have changed the IP address, sub mask and Router IP address. Since changing I have switched everything of and on again. Can anyone help?

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"IP and router address not consistent with subnet mask"

Hi all,
i have one of the old Powermac G5's running os x 10.3.5 "Panther" with a dual 2.5ghz processor, 512mb or ram, 160 gig hd, and no wireless card. I've been trying to hook the computer up to my network via an Ethernet cable (I have a Linksys WRT54G series router).
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What I've found is that no matter if the computer is plugged in with a cable to the Ethernet port the message comes up which is very unusual.
Thanks in advance.

Have you verified that you indeed have the proper subnet entered?
Why don't you just let the Mac obtain its ip address from the router via DHCP?

On my home wireless network, the iphone 5 won't let me enter the IP address, subnet mask and router info. I was able to enter the DNS and Search Domains. How do I open up those fields?

On my home wireless network, the iphone 5 won't let me enter the IP address, subnet mask and router info. I was able to enter the DNS and Search Domains. How do I open up those fields?

Apparently the router is not sending the info to the iphone. How can I make that happen?

Server and router on different subnets

Hello
Scenario 1.
A Server with one NIC assings DHCP addresses within the 192.168.1.x/24 network.
The internet router is on the 192.168.0.x/24 network.
How can the DHCP clients can access the Internet?
If the scenario requires adding another NIC, no problem.
Thanks
Kostas B.

Please explain your network setup further.
If you really need two subnets you must route between them and that could be achieved with OS X and two network interfaces.
Also if not using NAT in the server you need a static route in the Internet router pointing back at the second router IP on the same subnet and using that as the gw IP for the second subnet.
If you want to use VPN later using other network numbers is better.

I have a WiFi home connection. It works on my laptop but has stopped working on my iPad, which I tried resetting but it didn't help. It recognises the SSID but then asks for IP Address, Subnet Mask, Router etc. Any ideas on what to do?.

I have a WiFi home connection. It works on my laptop but has stopped working on my iPad, which I tried resetting but it didn't help. It recognises the SSID but then asks for IP Address, Subnet Mask, Router etc. Any ideas on what to do?.

1. Turn router off for 30 seconds and on again
2. Settings>General>Reset>Reset Network Settings

How to use the private subnet between ASA and Router

Guys,
Here is the context:
I am connecting to 2 ISPs for load sharing traffic coming from my private network.
The 2 links from the ISPs terminate in the router which connects to an ASA via a private subnet, back to my private network.
I have configured PBR in the router, to prefer ISP1 for trafic coming from my internal servers X, Y, Z (public addresses, no need for the ASA to translate). The router should send any other traffic coming from the rest of my private address space, servers W, V, U (after translation by ASA) to ISP2.
So far so good. The default route defined on ASA points to the internal LAN interface of the Router (private ip address). How can I route this subnet used between the ASA and Router? Being a private address I have to translate it to something (public) before the router can send it out. But translate to what?
Alternatively I could use a public subnet. But I do not have any.How do I get aroung this?
Regards
Ndaungwe

You have IP addresses on the direct interface links to the ISP's?? You ccould use those IP addresses with NAT overload.

On the initial set up for apple tv it just sits there trying to set the date and time . it is a wireless setup and the ipaddress and router address is correct . I can't get by this screen

On the initial set up for apple tv it just sits there trying to set the date and time . it is a wireless setup and the ipaddress and router address is correct . I can't get by this screen. The setting is on automatic and I have picked a city in my time zone yet it still tries to set a time and date but fails.
thanks

Make sure router is up to date. Try ethernet to rule out any wifi issues. Reboot ATV and router.

How do I add a Subnet and vlan with a catalyst 3550 and RV120

Hello Friends.
I have a scenario that i'm hoping i can get some help with. I'll be as detailed and descriptive as i can.
This is for a business with 100 employees nodes and 100 camera nodes all needing IP internet through private addressing and public gateway.
I have a business class gateway with a private range of 12 public addresses. Ther modem does nothing but act as a gateway since i have disabled the firewall and DHCP.
In place of the firewall and DCHP from the modem i have installed a RV120 Firewall with VPN. When installing i replicated the IP scheme of the modem as to not disturb and distrup the devices assigned addresses from that scheme from the modem. I did this because the owner could not have any down time or any disruption to the business operations.
The RV120 now acts as firewall , DHCP , and VPN. I'll address the subnet first. I's using 10.0.0.0/24 subnet range.
DHCP is assigning 10.1.10.50 - 10.1.10.100 the rest are static and i plan to use static DHCP with the IP and MAC assigned to each static DHCP address.
There are 100 cameras with static IP addresses in the range of 10.1.10.11 - 10.1.10.40, and 10.1.0.1.101 - 10.1.10.170.
VPN uses PPTP assigned address 10.1.10.6 - 10.1.10.10.
There are no layer 3 switches that i know of. Just a layer two that is the primary swith and ports have run out, and various out of the box switches and wireless access points connected to the primary switch.
I want to implement subnets into the network and VLANS as well on a new Layer 3 switche from cisco. Thinking 3550 from Cisco or one of the older layer 2 switches with layer three capabilities.
I also want to introduce a 192.168.0.0/24 IP range for the existing wireless network and segment the traffic from the rest of the traffic on other ranges.
I want to replace the 10.0.0.0/24 DHCP alltogether and the static addresses for end user nodes on the same network, but keep that range just for camera nodes segmented.
I want to implement a NEW end user IP range and VLAN for employee/guest networks using the 172.16.0.0/24 range.
Iv'e thought of replacing all the wireless nodes with RV120's and use VLAN. Dont know if that strategy works. Need to think it through.
I want the 192.168.0.0/24 IP range comunicate to with the 172.16.0.0/24 and possibly the 10.0.0.0/24 range.
Any advice on how to do this?
As a side note the next step after this is to install a server domain controller as all the computers are all stand alones in their own workgroups. It's a simultaneous project that will introdue a DCHP, WINS, DNS server.

Hi Omid, it sounds like you're proposing the 3550 switch but you're not decided yet. The 3550 switch is a pretty old device and needs enhanced multilayer image. It may be more prudent to use a more current switch such as small business SG300 or SG500 as the feature set is more rich and it supports around 480 LAN connections.
To answer the inquiry, the RV120W, when you create a VLAN it will automatically create an IP interface. From this you may assign subnet as you like along with 'enable or disable' for inter vlan routing. Since the RV120W has this feature, a layer 3 switch is not required unless you are looking to keep the routing load smaller by routing locally with the switch.
With Catalyst or a small business switch you would need to create a VLAN. After creating the VLAN, on a Catalyst you can simply issue "switchport trunk encapsulation dot1q" on the desired interface and all VLAN will passage without issue. For a port connecting a user "switchport mode access" "native vlan xx" This will assign the port as untag member of the desired VLAN.
If using a small business switch, it is slightly different, you still create the VLAN but the command issue is a bit different "switchport trunk allowed vlan add xx" for the link to the router, where xx = the VLAN ID to tag to the router. For access client it remains the same as Catalyst.

NAT and Routed Network with Two ISP's on one router

I'm sure this has been done covered many times, but I am not finding it.
I have two ISP connections.
With ISP-A I have a /30 between us and 200.100.100.0/24 is routed to me via the /30 for thsi example we will say the /30 is 1.1.1.1 on isp end and 1.1.1.2 on my end
With ISP-B I have a 100.0.0.0/29 subnet. and the ISP gateway is on that subnet at 100.0.0.1
On the inside of my network I have devices using both 200.100.100.x addresses and devices on 192.168.100.x that need to use NAT.
I would like all of the devices on 200.100.100.x addresses to continue using ISP-A as their gateway.
Everything on 192.168.100.x should use NAT and go out ISP-B
I have tried
ip nat inside source route-map ISP-A interface GigabitEthernet0/1 overload
route-map ISP-B permit 10
match ip address 101
match interface GigabitEthernet0/1
set ip next-hop 100.0.0.1
route-map ISP-A permit 10
match ip address 111
match interface Multilink1
set ip next-hop 1.1.1.1
The problem comes when I have default routes to ISP-A in the router than none of the ISP-B traffic works, and vice versa.

I think for this to work correctly and be able to split traffic between the 2 ISPs, you would need to use BGP, because default is going to use one ISP or the other.
If you can use BGP, this link will help you in load shearing between multiple ISPs when you have one router.
http://www.cisco.com/c/en/us/support/docs/ip/border-gateway-protocol-bgp/13762-40.html#conf4
HTH

GRE Tunnel/NAT with multiple subnets and interfaces

So, I am not sure if we are trying to accomplish too many things at once and what we are attempting to do is not possible or if we are missing something in our configurations...
Here is the situation...
We are migrating some equipment between datacenters. The equipment only a has a /27 worth of IP space assigned to it so we cannot simply "move" the IP space to the new datacenter. Further because we have several VPNs terminated in the old IP space that originate from devices we do not directly control and are essential in continuing to provide service, it was/is difficult to magically update some DNS entries and change IP addresses overnight. The last twist in this puzzle is that at the new datacenter, we will deploying some new equipment that will be in a separate subnet (with a separate Windows AD structure) but sharing the new public IP space we have in the new datacenter.
We thought using a GRE tunnel, some trunks, and a bunch of NATs would make the whole process easy and we tested ti in a lab and everything SEEMED to work. However, when we performed the move we ran into an odd issue that we were unable to figure out and had to go back to a failsafe configuration that has the essentials up and running, but the environment is not running in an ideal way for us to gradually transition as we would like.
Essentially what we had/have and how it was configured is as follows:
Site A
Edge Router - x.x.x.x /24 BGP announcement
x.x.x.y/27 that is within the /24 that we need at site b
GRE tunnel configuration
interface tunnel0
ip address 10.x.x.1 255.255.255.252
tunnel source <router edge IP>
tunnel destination <site b router edge ip>
keepalive 10 3
static route for site a public ip to bring it to site b via GRE tunnel
ip route x.x.x.y 255.255.255.224 10.x.x.2
Site B
Edge Router - y.y.y.y /24 BGP announcement
Similar GRE tunnel configuration (tunnel comes out and works so don't think issue is here)
2 Vlans (1 for site a ip space, 1 for site b ip space)
int vlan 50
ip address x.x.x.1 /27
int vlan 51
ip address y.y.y.129 /25
Trunk port for the VLANs going down to an ASA
int g1/1
swi mode trunk
swi trunk native vlan 51
swi tru all vlan 50,51
swi tru en dot1q
Then on the ASA, I have 2 physical interfaces for 4 logical interfaces (outside, outsideold, inside, insideold)
int e0/0
nameif outside
sec 0
ip address y.y.y.130 /25
int e0/0.50
nameif outsideold
sec 0
ip address x.x.x.2 /27
vlan 51
int e0/1
nameif inside
sec 100
ip address 192.168.y.1 /24
int e0/1.60
nameif insideold
sec 100
ip address 192.168.x.1 /24
vlan 60
A static route using the new ip space on the native outside interface...
route 0 0 y.y.y.129
And then I have some nat rules which is where I think things go a little haywire...
object network obj-y.y.y.0-24
subnet y.y.y.0 255.255.255.0
nat (inside,outside) dynamic interface
object network obj-x.x.x.0-24
subnet x.x.x.0 255.255.255.0
nat (insideold,outside) dynamic interface
object network obj-y.y.y.135-160
range y.y.y.135 y.y.y.160
object network obj-192.168.y.135-160
range 192.168.y.135 192.168.y.160
nat (inside,outside) static obj-y.y.y.135-160
object network obj-x.x.x.10-20
range x.x.x.10 x.x.x.20
object network obj-192.168.x.10-20
range 192.168.x.10 192.168.x.20
nat (insideold,outsideold) static obj-x.x.x.10-20
From some debugging and looking at packet-tracer, I found out I left out the below which was needed to properly nat traffic as it leaves the outside interface (when the default sends the traffic)
object network obj-192.168.x.10-20-2
range 192.168.x.10 192.168.x.20
nat (insideold,outside) static obj-x.x.x.10-20
There are / were a bunch of other nat exemptions for the VPNs and specific external routes to ensure all vpn traffic exited the "outsideold" interface which is where all the existing tunnels were terminated.
Everything appeared to be working great as all the VPN tunnels came up perfectly as expected and traffic appeared to be flowing, except for some of the most important traffic. The following was what was observed:
1. Any traffic using the dynamic NAT (ie...a machine with IP x.x.x.200 or y.y.y.20) would connect to the internet perfectly and work fine using the "new interface ip".
2. Any traffic in the "new range" using a one to one nat worked perfectly (ie y.y.y.140). Internet would work etc and nat translation would properly occur and everything could connect fine as expected.
3. ICMP packets to "old ip range" flowed perfectly fine to one to one nat IP (ie I could ping x.x.x.20 from outside) and likelise I could ping anywhere on the internet from a machine with a static natted ip.
4. Heres the butt...no traffic other than ICMP would reach these machines with static ips. Same range, same subnet as ones using the dynamic port translation that worked perfectly. Do not understand why this was / is the case and this is what I am seeking a solution to. I have attempted the following troubleshooting steps without success:
A. Confirmed MTU size was not an issue with the GRE tunnel. 2 methods, one plugging to edge router and using the "outsideold" ip space works perfectly and 2 if I assign outsideold ip space to "outside" interface, everything nats fine.
B. Ran packet-tracer, all results show "allow" as if I should be seeing the packets.
C. Confirmed local windows machine firewall was off and not blocking anything.
D. Reviewed logs and observed SYN timeouts and TCP teardowns as if the firewall is not getting a response and this is where I am stumped. There is no path around the firewall so asymmetric routing should not be an issue and if that was the problem it should not work when the "outsideold" ip space is assigned and natted from the "outside" interface, but it does. Packet-tracer shows proper nat translations occurring and there is definitely proper routing along the path for stuff to return to the network or ICMP would not work (IE I can ping www.google.com but not open the web page).
So what simple piece of the nat configuration am I overlooking because I cannot possible wrap my head around it being anything else.
Any suggestions / lessons would be greatly appreciated.

is this still a problem?

DHCP request through accesspoint and router

This is how our setup is like:
Laptops => Cisco 1100 AP(static IP) => Wired LAN (Subnet 1) => Cisco Router => Wired LAN (Subnet 2) => DHCP server
What i would like is that the DHCP-request from our laptops is forwarded/relayed through the AP and Router to the DHCP-server and back.
We dont want to use the AP's internal DHCP server but centralise this.
At the moment i'v configured the AP through CLI and added the following command: ip dhcp-server xx.xx.xx.xx
Where xx is the IP of the DHCP server
On the Router i'v added the command ip helper-address xx.xx.xx.xx
Where xx is the IP of the DHCP server
Don't know if this is the correct way, but i do know it isn't working.
Some help is realy appreciated.
Grx,
Joris

You need at least the following connectivity for DHCP relay to work.
Between the DHCP relay agent and the DHCP server:
- UDP Port 67 <-> UDP Port 67
Between the DHCP server and the DHCP client:
- UDP Port 67 <-> UDP Port 68 (renewing/releasing a lease)
- ICMP echo (Most DHCP servers check if an IP is still free)
On the Cisco router you can use some debugging commands
to check that relaying works.
(This might produce a lot of output, careful on a production system.)
#term mon
#debug ip dhcp server packet
#debug ip dhcp server events
For Subnet 1 with the router's IP 10.0.0.1 and two configured
DHCP servers (192.168.0.1, 192.168.9.1) as "ip helper" a successfull
exchange looks like this:
DHCPD: DHCPREQUEST received from client 0100.aabb.bbcc.cc.
DHCPD: setting giaddr to 10.0.0.1.
DHCPD: BOOTREQUEST from 0100.aabb.bbcc.cc forwarded to 192.168.0.1.
DHCPD: BOOTREQUEST from 0100.aabb.bbcc.cc forwarded to 192.168.9.1.
DHCPD: forwarding BOOTREPLY to client 00aa.bbbb.cccc.
DHCPD: Forwarding reply on numbered intf
DHCPD: creating ARP entry (10.0.0.49, 00aa.bbbb.cccc).
DHCPD: unicasting BOOTREPLY to client 00aa.bbbb.cccc (10.0.0.49).
#undebug all
I would also try to ping the router's IP in Subnet 1 and a client
with a fixed IP in Subnet 1 from the server. (The DHCP server uses
this to check if a lease is actually free before handing it out)
Otherwise it's time for packet sniffing on the DHCP server
and the client. (snoop, tcpdump, ethereal)

RV016: PPTP Server and "Block MAC address"

So if the PPTP server is enabled, and "Block MAC address not on the list" is enabled under the DHCP settings, will the PPTP client get an IP address?
Similarly, if the PPTP server is enabled and the range of IP addresses configured on the PPTP server screen is outside the IP range of the router due to a subnet mask (like 255.255.225.248 for example), will the IP still be assigned to the PPTP client? If assigned, will that IP have any connectivity to the LAN?
Thank you in advance for any answers!
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So here's how PPTP works with these two features:
1. The PPTP IP range is a different range than the DHCP range. You get an error message if your PPTP IP range overlaps with the DHCP one.
I didn't test the 'Block MAC' function because since the IP isn't coming from the DHCP pool, I highly doubt any MAC blocking will work.
2. Since your PPTP IP address range is outside of the DHCP range, this point is completely taken off the table. However, if you choose an IP range that's outside of the subnet, you'll get an error message when saving. I also learned that if you set the PPTP IP to just a single number and connect, the router will automatically reject any additional connections since no IPs are available.
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How to set up both static and DHCP assigned addresses on an AirPort Extreme

I recently bought an AirPort Extreme to replace my failed Cisco/Linksys router.
I am having trouble figuring out how I can configure the Extreme to support the already static IP addresses on my network as well as assign IP addresses via DHCP to a few devices where static IPs are not supported, i.e., work laptop.
Additionally, when DHCP is turned on, are my only options the 10.0, 172.16, and 192.168? What if I am running something like 10.10 or 172.30?
I am far from green when setting up computer networks, but this AirPort Extreme is making me pull my hair out.
BTW, I have access to a number of computers running a number of OSes including Windows XP, 7, and 8, as well as Mac OS X Snow Leopard and Mountain Lion.
The Mountain Lion or Windows 7 machine would be the preferred ones to configure the Extreme. I already have the AirPort Utility software running on them.
Any help would be appreciated.

I have found the 'DHCP Reservations' option on the AirPort Extreme to be buggy. I seem to remember it causing IP conflicts for some reason. I think what I remember is that if the computer with the reservation was off, and the DHCP server then handed out that IP to another DHCP client, then there would be a conflict when the reserved IP computer was turned back on. Maybe it was an issue in ealier versions of the AE or OS X as the case may be, and maybe it's been corrected, but I've never bothered using it agian since the method I describe below has always worked without fail. Also, I'm guessing DHCP Reservations would work fine if one manually enters IPs outside of the DHCP range but in the AE 'DHCP Reservation Setup Assistant' the IP options provided are within the DHCP range which to me makes no sense and increases the potential for IP conflicts.
Here's what I do to setup a mixed environment of static and dynamic IPs on my network. It works like a charm and does not require the DHCP server (beyond the distribution of dynamic IPs to hosts using DHCP).
For machines on my network that are accepting services from the public network, I set them up with static IPs using the 'Manually' option (System Preferences/Network/Ethernet/Configure IPv4). The settings for 'Router' IP address and 'DNS Server' IP address should both be set with your gateway/router LAN IP). Use an IP address below or above the DHCP range of adresses (in AE/Internet/DHCP/DHCP Beginning & Ending Address).
i.e. if my subnet is 10.0.1.1 and my DHCP range is 10.0.1.100 to 10.0.1.150, you could set the static IPs on your local hosts as 10.0.1.x where x = any number from 2 - 99 or from 151 - 200 as an example.
All other machines and devices that do not require static routing are setup as DHCP clients and get a dynamic IP from the AE. To me it's a simpler setup though it might take a little extra time to setup initially.
John

Subnetting and router ip addresses

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