[IPv6] Newbie questions about ipconfig output


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Winfried

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Hello,

I'm learning about IPv6 and would like to understand the output from the "ipconfig" command:
  1. Is the "Link-local IPv6 address" for local use because it's non-routable, while the "IPv6 address" is used by hosts when interacting with hosts on the Internet, eg. web servers?
  2. Are IPv6 addresses assigned to hosts generated dynamically? If so, what device handles that task? The DHCP server running on the router?
  3. If a host has both IPv6 and IPv4 addresses recorded in the DNS, do web browsers first try connecting through its IPV6 address, and then try IPv4 if it fails?
  4. If the router has no firewall, does it mean hosts with an IPv6 are not protected from connections from the web, and must thus run their own firewall?
Thank you.

c:\>ipconfig /all
Ethernet adapter Ethernet:
Connection-specific DNS Suffix . :
DHCP Enabled. . . . . . . . . . . : Yes
Autoconfiguration Enabled . . . . : Yes
IPv6 Address. . . . . . . . . . . : 2a01:XXX:590:fd80:1a08:50b2:881d:2947(Preferred)
Link-local IPv6 Address . . . . . : fe80::XXX:963:5027:aacd%20(Preferred)
Default Gateway . . . . . . . . . : fe80::XXX:cbff:fe91:be45%20
DHCPv6 IAID . . . . . . . . . . . : 3020XXX08
DHCPv6 Client DUID. . . . . . . . : 00-XX-00-01-XX-B8-0F-1C-00-E0-XX-45-XX-F2
 

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Winfried said:
Hello,

I'm learning about IPv6 and would like to understand the output from the "ipconfig" command:
  1. Is the "Link-local IPv6 address" for local use because it's non-routable, while the "IPv6 address" is used by hosts when interacting with hosts on the Internet, eg. web servers?
  2. Are IPv6 addresses assigned to hosts generated dynamically? If so, what device handles that task? The DHCP server running on the router?
  3. If a host has both IPv6 and IPv4 addresses recorded in the DNS, do web browsers first try connecting through its IPV6 address, and then try IPv4 if it fails?
  4. If the router has no firewall, does it mean hosts with an IPv6 are not protected from connections from the web, and must thus run their own firewall?
Thank you.
Click to expand...
Something I hope will help improve your knowledge of IPV6.

About question 3, the OS, not the browser(s) can be configured to use IPv4 or 6.

learn.microsoft.com

Configure IPv6 for advanced users - Windows Server

Provides step-by-step guidance for how to use the Windows registry to disable IPv6 or certain IPv6 components in Windows.
learn.microsoft.com

About question 4, no firewall = no protection after the router.

'Not having a firewall' lists the risks:

www.itsasap.com

3 Top Risks of Not Having a Firewall

Not having a firewall for your business is a disaster waiting to happen. While it’s not perfect, skimping on a firewall can have dire consequences. Find out what a firewall does for your network, and the risks you might encounter if you don’t have one.
www.itsasap.com www.itsasap.com
 
Last edited:

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1a. Is the "Link-local IPv6 address" for local use because it's non-routable,
Click to expand...
Correct. The IPv4 speak the equivalent would be a 169.254.x.x address. The difference being in IPv6 you will always have a link local address since it is not optional.

1b. .. while the "IPv6 address" is used by hosts when interacting with hosts on the Internet, eg. web servers?
Click to expand...
Yes .. mostly-ish because .. it depends. If the destination is not configured to speak IPv6 and no NAT64 services are in use then IPv6 transport will fail. If the destination does not have an AAAA record in DNS for the resource IPv6 transport will fail.

2a. Are IPv6 addresses assigned to hosts generated dynamically?
Click to expand...
Yes, no and it also depends. :D

Yes when invented by the SLAAC process using Router Advertisements (RA). No when addresses are assigned by DHCPv6. Depends with Teredo since that IP address is constructed based upon several inputs that may or may not change.

2b. If so, what device handles that task? The DHCP server running on the router?
Click to expand...
Depends on who/what is creating the address. See 2a.

3. If a host has both IPv6 and IPv4 addresses recorded in the DNS, do web browsers first try connecting through its IPV6 address, and then try IPv4 if it fails?
Click to expand...
Depends. The first needed item is does the destination resource have a AAAA record in DNS? If no, then IPv6 transport will not happen. If yes, then "Happy Eyeballs" algorithm (should) kicks in.

4. If the router has no firewall, does it mean hosts with an IPv6 are not protected from connections from the web, and must thus run their own firewall?
Click to expand...
Super splitting hairs here but a legit router does not have firewall. Consumer grade networking equipment often colloquially referred to as a "router" often times will have the ability to shape traffic via different methods but as with everything else .. it depends on who make the hardware in service to give an accurate answer as opposed to the yes/no you are looking for.

Hope the extra context is helpful.
 

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Thanks much.

I found O'Reilly's "IPv6 Essentials" a bit hard to read, unlike Cisco's " IPv6 Fundamentals A Straightforward Approach to Understanding IPv6".

So "Link-local IPv6" is even more local than I thought if they can't be used for two hosts to communicate over the same LAN.

Good to know about the Happy Eyeballs algo.

My older router has no firewall for IPv6, which startled me when I could connect from the Net with a smartphone to a test web server running locally. I later learned that NAT is limited to IPv4. Until I upgrade soon to a more modern connection, I'll add a software firewall on that server.

A more recent hardware at a friend's house does have a firewall for IPv6 (in addition to NAT for IPv4), which got me stuck for a few minutes until I spotted that section. I couldn't figure out why the local web server wasn't reachable from the Net.

Consumer grade networking equipment often colloquially referred to as a "router" often times will have the ability to shape traffic via different methods but as with everything else .. it depends on who make the hardware in service to give an accurate answer as opposed to the yes/no you are looking for.
Click to expand...

Why the quotes? Isn't an ADSL/fiber box a router?
 

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Yet more questions…

For security reason I guess, to connect to the Net, does Windows always generate temporary IPv6 addresses?

When does it actually use the real IPv6 address?

How long do they remain active? Why create more while others are still available?

Code: 
c:\>ipconfig
Windows IP Configuration
Ethernet adapter Ethernet:
   Connection-specific DNS Suffix  . :
   IPv6 Address. . . . . . . . . . . : x:x:x:x:1a08:50b2:881d:2947
   Temporary IPv6 Address. . . . . . : x:x:x:x:2062:7c27:8a99:d4e2
   Temporary IPv6 Address. . . . . . : x:x:x:x:2923:6c09:62e2:c728
   Temporary IPv6 Address. . . . . . : x:x:x:x:51b4:4702:a63d:679
   Temporary IPv6 Address. . . . . . : x:x:x:x:d8fb:f8c5:f14e:4e98
   Link-local IPv6 Address . . . . . : fe80::x:x:x:aacd%21
 

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Temporary addresses are created to prevent websites from tracking you by recording a fixed IP.

You can find your current expiration times using PowerShell:
Code: 
PS C:\Users\GARLIN> Get-NetIPv6Protocol

DefaultHopLimit               : 128
NeighborCacheLimit(Entries)   : 256
RouteCacheLimit(Entries)      : 4096
ReassemblyLimit(Bytes)        : 33546080
IcmpRedirects                 : Enabled
SourceRoutingBehavior         : DontForward
DhcpMediaSense                : Enabled
MediaSenseEventLog            : Disabled
MldLevel                      : All
MldVersion                    : Version2
MulticastForwarding           : Disabled
GroupForwardedFragments       : Disabled
RandomizeIdentifiers          : Enabled
AddressMaskReply              : Disabled
UseTemporaryAddresses         : Enabled
MaxTemporaryDadAttempts       : 3
MaxTemporaryValidLifetime     : 7.00:00:00 <- 7 days
MaxTemporaryPreferredLifetime : 1.00:00:00 <- 1 day
TemporaryRegenerateTime       : 00:00:05
MaxTemporaryDesyncTime        : 00:10:00
DeadGatewayDetection          : Enabled

If you don't like your current settings, Get-NetIPv6Protocol can change them.
 

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