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Sky-5
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Auto IP Aliasing ?

Questions

1. I understand that IP aliasing provides additional IPs for lan and wlan but what is their purpose ? What is anyone using them for ?

2. As default, Auto IP Aliasing is enabled. If I'm not using them, should I disable them ?

Thanks
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vaden
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Re: Auto IP Aliasing ?

Questions

1. I understand that IP aliasing provides additional IPs for lan and wlan but what is their purpose ? What is anyone using them for ?

2. As default, Auto IP Aliasing is enabled. If I'm not using them, should I disable them ?

Thanks


We requested what Ubiquiti calls Auto IP Aliasing in 2006 based on the desirability of auto-configuration and RFC 3927 (see <>).

The genesis came from roof.net, but we were not and are not interested in mesh. Instead, what we were after was to make setup easier so the installer did not have to have so much knowledge, but could concentrate on the alignment LEDs and Knock Your Socks Off Customer Service.

roof.net used 10.mac4.mac5.mac6; what Kestutis et al implemented was 169.254.mac5.mac6, following RFC 3927.

We also asked that mac telnet be implemented in order to allow the network operations center of a WISP to grab control and stuff a standard configuration. This has yet to be done.

It is compatible with MikroTik's implementation of Universal Client.

Does that answer your question? If not, I will try again.

kind regards/ldv
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wirelessrudy
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Re: Auto IP Aliasing ?

Well, to me it doesn't make much sense. But can the default option (enabled) be disabled? Or does it makes no difference at all?
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wirelessrudy
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Re: Auto IP Aliasing ?

Ok, never got any more info on this one.

I actually want to ping to a wifi router that is behind a NS in routing mode.
I can reach that wifi router from the WAN with port forwarding. But this is just a http connection to a port 8080 while I reach the antenna's with another port number.

But to send a ping through the router to a specific LAN IP address. How to do that.
In MT CPE I just set a second IP on WAN port as the main, and make that second IP dst-nat to the LAN IP of choice. (And that LAN IP of choice has a specific src-nat to that second IP)

I am hoping to something similar on the nanostations. I was hoping that IP aliases could help me here.

Same sort of issue I have is that I want Skype phones behind a routed NS to go out onto the WAN (= internet) with a different IP address as all the rest of the traffic leaving from, or through this NS.

This is actually the only 100% sure methode of capture all Skype traffic.

rgds.
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Maelos
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Re: Auto IP Aliasing ?

Well, to me it doesn't make much sense. But can the default option (enabled) be disabled? Or does it makes no difference at all?


I am not entirely sure what IP Aliasing does, but we do not need it, and so, disable it. Every CPE, every AP, every time. I have seen CPEs and APs get stupid behind the WAN from time to time, and every single one had IP Aliasing turned on. Disabling it seemed to resolve issues. This could be, and likely is, unrelated to IP Aliasing, but just some anecdotal experience from the field.

Again, I know nothing about IP Aliasing, Im sure it works wonders when used for its intended purpose. We have no use for it on our network, and so disable it with no noticeable issues.
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UBNT-Matt
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Re: Auto IP Aliasing ?

Basically it allows for device manageability/accessibility if you lose/misconfigure/forget the devices main IP.
The auto-alias IPs are based on the last 2 octets of the MAC address, so you can determine what the IP is if you know the MAC.
-Matt
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succeednet
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Re: Auto IP Aliasing ?

OK so heres a dumb question. How do you convert the MAC to and ip address?
NM i figured it out. Convert HEX to Decimal
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UBNT-Matt
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Re: Auto IP Aliasing ?

OK so heres a dumb question. How do you convert the MAC to and ip address?


From Wiki:
Auto IP Aliasing configures automatically generated IP Address for the corresponding WLAN/LAN interface if enabled. Generated IP address is the unique Class B IP address from the 169.254.X.Y range (Netmask 255.255.0.0) which are intended for use within the same network segment only. Auto IP always starts with 169.254.X.Y while X and Y are last 2 digits from device MAC address (i.e. if the MAC is 00:15:6D:A3:04:FB, Generated unique Auto IP will be 169.254.4.251).

If you take the last two octets from the MAC (in this case 04 and FB) and convert them from hex > decimal, it will give you the last two digits of the IP:
www.google.com/#sclient=psy&hl=en&q=0x04+in+decimal&aq=f&aqi=&aql=&oq=&gs_rfai=&pbx=1&fp=ca05a7bb65e...
www.google.com/#sclient=psy&hl=en&q=0xfb+in+decimal&aq=f&aqi=&aql=&oq=&gs_rfai=&pbx=1&fp=ca05a7bb65e...

0x04 = 4
0xfb = 251

Hope that helps,
Matt
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Schnulch
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Re: Auto IP Aliasing ?

you can use windows calculator or any other calc, that is capable of doing hex and decimal system.
if the mac of your device is for instance: 00:15:6d:2a:3f:4d
you set the calculator to HEX, enter 3f, change to decimal, and voila, you see 63.
then you enter 4d into your calculator in Hex mode, switch to decimal, and get: 77
Since all alias IP's are of 169.254.x.x range, you get 169.254.63.77 as the ip
too slow...
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sstof
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Re: Auto IP Aliasing ?

I am not entirely sure what IP Aliasing does, but we do not need it, and so, disable it. Every CPE, every AP, every time. I have seen CPEs and APs get stupid behind the WAN from time to time, and every single one had IP Aliasing turned on. Disabling it seemed to resolve issues. This could be, and likely is, unrelated to IP Aliasing, but just some anecdotal experience from the field.

Again, I know nothing about IP Aliasing, Im sure it works wonders when used for its intended purpose. We have no use for it on our network, and so disable it with no noticeable issues.

Maleos,
I have to second your experience with Auto IP Aliasing. The very first thing I do is turn it off when Im setting up units. I use Nano's in Bridge mode for a non WISP purpose. I found out real quick that AutoIP is 1. enabled by default and B. will make you pull your hair trying to communicate to devices attached to stations.
Making Something out of Nothing
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vaden
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Re: Auto IP Aliasing ?

Basically it allows for device manageability/accessibility if you lose/misconfigure/forget the devices main IP.

The auto-alias IPs are based on the last 2 octets of the MAC address, so you can determine what the IP is if you know the MAC.

-Matt


Matt et al, the feature is useful in the following additional situations:

1. Initial configuration --- one can set a WinDoze laptop to dhcp (which won't be satisfied) and hook up to a Ubiquiti device and use the Ubiquiti Discovery Tool to browse to the unit without further ado.

2. During the occasional house call, one can do the same thing.

3. Since it follows the MIT roofnet protocol for addressing (more or less, UBNT's choice of 169.254.0.0/16 was even better, IMHO), it is quite useful if you are running a routed network with less than 65,536 CPE.

4. I am quite sure there are other uses as well.

I have never seen an instance in five years that this feature caused a problem. Quite to the contrary.

regards/ldv

---------- Forwarded message ----------
From: Larry Vaden
Date: Wed, Nov 29, 2006 at 8:54 AM
Subject: Re: Re: Internet Texoma: thanks for your phone call
To: "Robert J. Pera"
Cc: Linus Lin

. autoconfiguration option based on mac address (see MIT's RoofNet, e.g.)
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mhoppes
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Re: Auto IP Aliasing ?

I really still don't see the usefulness, but maybe I'm missing something....

1. Initial configuration --- one can set a WinDoze laptop to dhcp (which won't be satisfied) and hook up to a Ubiquiti device and use the Ubiquiti Discovery Tool to browse to the unit without further ado.

Isn't this what the default 192.168.1.20 address is for? And I don't need to discover... I just always know the IP of a new Ubiquiti device.


2. During the occasional house call, one can do the same thing.

At least for us, we run in router mode for our clients, which means all radios have an internal IP of 10.200.90.1 Again, no guessing. The tech always knows the IP of the radio.


3. Since it follows the MIT roofnet protocol for addressing (more or less, UBNT's choice of 169.254.0.0/16 was even better, IMHO), it is quite useful if you are running a routed network with less than 65,536 CPE.

I now understand better what the desire was with Auto-IP aliasing... and have to say I completely disagree with it. Mesh networking is almost always done because someone wants to throw up a network without proper channel/distance/throughput/etc planning. Auto-IP just adds to that disaster.

Maybe it works for you.... but for me, if there is a device out on my network I want to know what it is, what it's IP is, and why it's there. I don't want things just "auto-configuring" themselves.
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vaden
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Re: Auto IP Aliasing ?


What about excessive ARP traffic ARPing for IPs that shouldn't even be on the network anyway?

Maybe it works for you.... but for me, if there is a device out on my network I want to know what it is, what it's IP is, and why it's there. I don't want things just "auto-configuring" themselves.


Please _do all of us a favor_ and present a tcpdump that shows the "excessive ARP traffic" or withdraw the remark.
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mhoppes
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Re: Auto IP Aliasing ?

Please _do all of us a favor_ and present a tcpdump that shows the "excessive ARP traffic" or withdraw the remark.


Any ARP traffic for an IP that doesn't belong on my network is excessive.
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vaden
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Re: Auto IP Aliasing ?

Any ARP traffic for an IP that doesn't belong on my network is excessive.


OK, if you don't want to be faced with the reality of tcpdump, perhaps you will read RFC 826, "An Ethernet Address Resolution Protocol," which says, in part:


Why is it done this way??
-------------------------

Periodic broadcasting is definitely not desired. Imagine 100
workstations on a single Ethernet, each broadcasting address
resolution information once per 10 minutes (as one possible set
of parameters). This is one packet every 6 seconds. This is
almost reasonable, but what use is it? The workstations aren't
generally going to be talking to each other (and therefore have
100 useless entries in a table); they will be mainly talking to a
mainframe, file server or bridge, but only to a small number of
other workstations (for interactive conversations, for example).
The protocol described in this paper distributes information as
it is needed, and only once (probably) per boot of a machine.


Now, I ask you again, please withdraw the misinformation before some n00b reads it and thinks it is gospel.
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upwardaccess
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Re: Auto IP Aliasing ?

Any ARP traffic for an IP that doesn't belong on my network is excessive.


Agreed, Any ARP traffic on the network that isn't necessary is just clutter. Auto IP Alias is just that...clutter. We truned it off months ago on all radios and it's cleared up a ton of strange network problems.
I don't care if it's a feature but should be off by default
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mhoppes
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Re: Auto IP Aliasing ?


Now, I ask you again, please withdraw the misinformation before some n00b reads it and thinks it is gospel.


Consider it done. I still think letting things auto manage themselves is bad practice, but to each his own.
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mhoppes
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Re: Auto IP Aliasing ?

Agreed, Any ARP traffic on the network that isn't necessary is just clutter. Auto IP Alias is just that...clutter. We truned it off months ago on all radios and it's cleared up a ton of strange network problems.
I don't care if it's a feature but should be off by default


+1 Yes, have it there, but turn it off. It's one of the first things that gets done to our template configuration files.
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mhoppes
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Re: Auto IP Aliasing ?

OK, if you don't want to be faced with the reality of tcpdump, perhaps you will read RFC 826, "An Ethernet Address Resolution Protocol," which says, in part:


Larry,
I have 'excessive ARPing' for IPs that I own but which aren't assigned to anything. Somebody port scans or sniffs IPs from the Internet, or someone has a virus on the network. I've done TCPDUMP and I've seen the traffic.

We obviously disagree on this, so I think it's probably best if we just let it go at that.
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vaden
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Re: Auto IP Aliasing ?

Larry,
I have 'excessive ARPing' for IPs that I own but which aren't assigned to anything.

According to ARIN, you don't 'own' any IPs.

Somebody port scans or sniffs IPs from the Internet, or someone has a virus on the network. I've done TCPDUMP and I've seen the traffic.

If you are accepting traffic from the Internet for the 169.254.0.0/16 network, you are accepting traffic for BOGONs.

We obviously disagree on this, so I think it's probably best if we just let it go at that.

Just me and the folks who live by the RFCs written by the giants on whose shoulders we stand.