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Standard User meditator
(fountain of knowledge) Tue 02-Dec-14 11:43:52
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Fixed IPs: do you always have to use an ARP table?


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For various reasons that I don't need to expound here, I use fixed IP addresses on my home network, and at present Internet access, at least, seems to work okay - aside from the occasional slowness in resolving, which may or may not be down to the browser. There are three devices on the network, two of which are computers. I don't regard myself as an expert in configuring for fixed IP LAN addresses and so I'm wondering if I've done sufficient to set this up properly. When you use fixed IP addressing as opposed to DHCP, do you always have to set up an ARP table in the router? I've just changed my router, to a new Billion 8800NL (used in ADSL mode for the time being).

As far as I can see, the 8800 has a dedicated place for configuring ARP. In the 8800's GUI it's found at Advanced Setup >> Static ARP. If inserting the IP addresses of all the LAN devices into this table is always essential (and that's the question really), where do I acquire the MAC addresses, as the table requires me to input both the IPs and their MAC addresses?

At present the ARP table is completely empty. However, if I look in Status >> ARP, I see the IP address of the computer I'm using at the time (but not the IPs of the other devices, whether they're in use or not). One of the devices on the LAN is a printer.

So, when you use fixed IP addressing do you always have to also set up an ARP table in the router? Does having an ARP table make for more efficient resolution, in any event?

I've not hitherto used an ARP table because it was my understanding that this was required only for situations where you needed to perform MAC filtering, which isn't the case here. But maybe, quite aside from that, an ARP table is still required? Otherwise, how can one device on the LAN know the address of another on the same LAN, other than enquiring on the router?

Can someone enlighten me?

Note: I observe that you can see the MAC address of each computer if you log into the router with each one. But obviously I'm not able to do this in the case of the printer. So, if I DO need to set up a table, how can I find out the MAC address of the printer?

Edited by meditator (Tue 02-Dec-14 11:55:11)

Standard User Adrian
(experienced) Tue 02-Dec-14 13:39:24
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Re: Fixed IPs: do you always have to use an ARP table?


[re: meditator] [link to this post]
 
I am assuming here that you mean fixed LAN addresses, ie 192.168.1.1 etc.

I have a Billion 7800DXL, which has a similar configuration set up to the 880 and I assign static IPs using the LAN configuration page. About half way down there is a section called "Host Label". Just click on "Add", type in a name for the device, the MAC address of the device and the static IP number you want. Done!

I played around with ARP originally but apparently that isn't the right way to do it, but don't ask me why.

Can't you get the printer's MAC address from the printer configuration page?

Adrian

Edited by Adrian (Tue 02-Dec-14 13:42:22)

Standard User ian72
(eat-sleep-adslguide) Tue 02-Dec-14 14:45:40
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Re: Fixed IPs: do you always have to use an ARP table?


[re: meditator] [link to this post]
 
As long as the static IPs are all in the same subnet and you have the router IP as the gateway and appropriate DNS settings (DNS can either be the router itself or direct to external DNS servers such as openDNS or the ISPs own DNS) then you don't need to configure anything at the router (well, except changing the DHCP scope or turning it off to ensure DHCP doesn't hand out the same address as you have used as a static).

The router and network will take care of itself with no advanced config required - especially with only 3 devices.


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Standard User sfo32
(newbie) Tue 02-Dec-14 15:03:37
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Re: Fixed IPs: do you always have to use an ARP table?


[re: meditator] [link to this post]
 
No you don't really need to worry about ARP tables.

There are two ways to use static IPs within your private network.

The simplest in *my* opinion, is to configure a fixed IP on each device individually (e.g. on a Windows PC, go to the IPv4 properties for the network interface and set a static IP there, along with a gateway and DNS resolvers).

You can then leave the router with all its default settings, even DHCP, so that any device you add to your network, even temporarily, will get an IP and DNS automatically.

To stop DHCP allocating an IP that you have already manually configured, you can configure the router's DHCP IP allocation range to, say, 192.168.1.2 to 192.168.1.99, and then use .100 and upwards for your manually set IPs.

In this way you don't need to care about MACs, or about having to reconfigure the IPs in the router if you replace it or reset it to factory defaults for any reason.

Although I think this is the simplest way, many would disagree. YMMV

The other way of doing things is to get the router to always allocate a particular IP to a device with a particular MAC. This seems to be what you have been attempting to do and there's absolutely nothing wrong with it. It involves DHCP, but you are enforcing which IP gets allocated when a device with a particular MAC asks for an IP. You don't need to tell each PC which IP to use, what DNS servers to use and what gateway to use, which is great, and you typically have one place in the GUI with a nice list of what is allocated what. And if you almost never change devices, or reset your router, it could well be the simplest option.


Note that you can use a combination of all these things if you like. That's actually what I do. I have the router set to allocate random DHCP IPs under .100, then 100, 101 etc are manually set IPs, and there's once device (a printer) that's such a pain in the neck to change its IP that I use MAC to IP binding to do so.

Incidentally, you should be able to get a printer's MAC by making it print out a status page for its network configuration, or it may be printed on the label or near the network port.

There are also some wonderful little utilities you can use. If you search for SoftPerfect WiFi Guard, you'll find one such free utility that will go through all the IPs in your network, and show you the MAC associated with them. It will usually give you a manufacturer, which can sometimes help you identify the device but not always (e.g. a Sky digibox shows up with a vendor of BSkyB, which is great, but sometimes you'll get no vendor listed, or the vendor will be for the network card which may be different to the manufacturer of the actual device as a whole).

Once you positively identify what's what, you can add your own description/name to each device so you never forget what's what.
Standard User meditator
(fountain of knowledge) Tue 02-Dec-14 15:32:49
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Re: Fixed IPs: do you always have to use an ARP table?


[re: Adrian] [link to this post]
 
Yes, that's right, the LAN IP addresses.

I found the setting called 'Host Label'. It comes under a section called 'Static IP List', so at first sight it seems relevant. However, this host labelling is apparently for when the DHCP server assigns IP addresses (see the notes surrounding that section in your 7800DXL's user manual) and, by definition, I don't use DHCP. The router in my case is not acting as a distributor of LAN IP addresses. DHCP is completely off. The fixed IP addresses have been assigned manually by ME, using the appropriate settings in the computers and in the printer.

I'm not sure what you mean by the 'printer configuration page'. The only such page that I can recall is a printout that can be done, once the printer has been manually configured, that tests the operation of the printer. Among the results, it prints a few parameters, eg, the IP address you've given it. However, I've never seen a MAC address.

Possibly, your fixed IP setup is working, despite your use of Host Label, rather than because of it?
Standard User meditator
(fountain of knowledge) Tue 02-Dec-14 16:11:09
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Re: Fixed IPs: do you always have to use an ARP table?


[re: ian72] [link to this post]
 
Ian, what you've described is exactly as I've got it. The three fixed LAN IPs I've chosen to use lie well outside the normal range - but obviously still in the same subnet - of DHCP. Note that DHCP is fully turned off, so there should never be any chance of a clash between nos. in the DHCP range and ones that I myself have chosen to use. I assigned the IP addresses manually into the Network settings of both computers, also inserting DNS addresses. For DNS, I use the DNS server of my ISP as the primary one, and Google's DNS server as the secondary one. For the gateway device, the router's LANside address is used.

Of course, it's not possible to set DNSs in the printer; or at least you can't in MY printer; all you can do with the printer is to manually assign it an IP address and a subnet address (a laborious exercise that has to be done using frontpanel buttons in combination with the printer's character-strip frontpanel indicator). But once done, you don't have to bother again.

So, it rather looks as though I've done things correctly and therefore don't need to do anything further, especially constructing an ARP table. If that's the case, then great!

Prior to the changeover to the 8800 as my router I'd used the router's LANside address as the DNS Server (rather than giving the various devices my ISP's DNS server as the DNS), with DHCP turned off, and that certainly did seem to work, although I always had a nagging feeling that the configuring was still incomplete and therefore the resolving was probably never working optimumly. I imagine that with the router as DNS server, the router effectively acts as a relay device, since I guess it must still need to access an external DNS server in order to resolve website IPs.
Standard User meditator
(fountain of knowledge) Tue 02-Dec-14 16:36:52
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Re: Fixed IPs: do you always have to use an ARP table?


[re: sfo32] [link to this post]
 
Oh good. ian72 has reassured me also that I've been doing things correctly. The only slightly different thing I've done to what you yourself have suggested is to turn DHCP completely off. I've used LANside IPs that are well away from any that DHCP would use but which are in the same subnet.

If you read my reply to ian72, you'll be able to gather more details of my implementation. I can't see that the router can be allocating any fixed addresses to the devices in my case, though, as I've DHCP off and I haven't otherwise told the router precisely which fixed addresses are involved. The addresses merely exist in the particular devices, as assigned manually into the devices by me. (This is why I've always had a suspicion that the router requires some sort of lookup table).

As regards finding a MAC address for my printer, if I now ever have to, this remains for the moment unsolved. I've looked over the labels on the back of my printer but there's nothing there that looks remotely like a MAC address. The printer is a laserjet that goes way back to the 1990s. I don't ever recall seeing its MAC address being on a test printout either. Would a ping to the printer return its MAC address?
Standard User ian72
(eat-sleep-adslguide) Tue 02-Dec-14 16:39:04
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Re: Fixed IPs: do you always have to use an ARP table?


[re: meditator] [link to this post]
 
The printer doesn't need DNS as it doesn't need to connect out to anything by name. So, yes, it sounds like everything should be fine as you have it. The router will pass off DNS calls to an external DNS server - the benefit of using the router address is if the IPs of the DNS change then it can pick the changes up from the ISP without you having to do anything (assuming you use the ISP DNS servers). Even if you add them manually it means just one place to change them if needed.
Standard User ian72
(eat-sleep-adslguide) Tue 02-Dec-14 16:42:35
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Re: Fixed IPs: do you always have to use an ARP table?


[re: meditator] [link to this post]
 
I can't test the theory here at the moment but...

Have a go at first pinging the IP address of the printer from one of the PCs. You should get responses.

Then, using the arp command (I think arp -a) you should be able to get the table of address resolutions on your PC which should include the IP and MAC of the printer.
Standard User b4dger
(knowledge is power) Tue 02-Dec-14 17:47:12
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Re: Fixed IPs: do you always have to use an ARP table?


[re: meditator] [link to this post]
 
In reply to a post by meditator:
As regards finding a MAC address for my printer, if I now ever have to, this remains for the moment unsolved. I've looked over the labels on the back of my printer but there's nothing there that looks remotely like a MAC address. The printer is a laserjet that goes way back to the 1990s. I don't ever recall seeing its MAC address being on a test printout either. Would a ping to the printer return its MAC address?
If this is a 20 year old printer are you sure it's on your network and not just connected directly to a PC?

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