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Clever_Proxy
Premium
join:2004-05-14
Villa Park, IL

[IPv6] Static IPv6 address assignment on a dynamic prefix

Sorry if this question is a little noob-ish...

When dealing with DHCP6 with Prefix Delegation, how do we define static addresses on a network?

Let's say I have a prefix of 2001:1234:1234:1234::/64 and I wanted 2001:1234:1234:1234::dead:beef:cafe to be statically assigned to an interface, how do I prevent DHCP from assigning that address to another interface?

Of course, the chance of that happening is very slim, I'm still just curious of how that would be handled.



kontos
xyzzy

join:2001-10-04
West Henrietta, NY

I'm speaking with no real-world experience here, but I understand it that a DHCPv6 PD assignment from your ISP tells the DHCP client in your router what IPv6 prefix to use. If the router also has a DHCPv6 server, it would have to use that information to create its scopes for assigning addresses. You would just have to make sure your static address is outside of your DHCPv6 server scopes.



graysonf
Premium,MVM
join:1999-07-16
Fort Lauderdale, FL
kudos:2
reply to Clever_Proxy

Assign a range of addresses for the network's DHCP6 server that does not include the address(es) you assign statically.


voiptalk

join:2010-04-10
Gainesville, VA

1 recommendation

said by graysonf:

Assign a range of addresses for the network's DHCP6 server that does not include the address(es) you assign statically.

That's pretty much it.

However, the is no guarantee that of how long you will keep that IPv6 prefix assigned by Comcast. Just like an IPv4 address, they could hand out a different one due to readdressing or whatever. So, if you statically assign addresses from the initial DHCP-PD provided prefix, you could be dead in the water until you re-address the statics.

Also, most "home routers" do not do DHCPv6 for LAN address assignment anyway. It's Stateless Auto Config. The router advertises the prefix it got and the hosts generate their own IPv6 address. In that case there is Duplicate Address Detection.


graysonf
Premium,MVM
join:1999-07-16
Fort Lauderdale, FL
kudos:2

Well, you pays your money and takes your chances with dynamic IP assignments, so sure, you could shoot yourself in the foot this way.

I don't have one of those "home routers" so I can set myself up for shooting myself in the foot just fine.

It's all moot for me right now, no Comcast native IPv6 here yet.



kara

@comcast.net
reply to Clever_Proxy

also don't bother techsupport for help on this its dhcp service or buy static ip on business class



NetFixer
Freedom is NOT Free
Premium
join:2004-06-24
The Boro
Reviews:
·Cingular Wireless
·Comcast Business..
·Vonage

said by kara :

also don't bother techsupport for help on this its dhcp service or buy static ip on business class

Having a business class static IP account is actually a good way to avoid the hassle of IPv6, since Comcast does not currently support IPv6 (except for outbound usage with a 6to4 relay) for their static IP business class service (not with the service itself or with the required SMCD3G gateway).
--
We can never have enough of nature.
We need to witness our own limits transgressed, and some life pasturing freely where we never wander.


NetDog
Premium,VIP
join:2002-03-04
Parker, CO
kudos:79
reply to Clever_Proxy

said by Clever_Proxy:

Sorry if this question is a little noob-ish...

When dealing with DHCP6 with Prefix Delegation, how do we define static addresses on a network?

Let's say I have a prefix of 2001:1234:1234:1234::/64 and I wanted 2001:1234:1234:1234::dead:beef:cafe to be statically assigned to an interface, how do I prevent DHCP from assigning that address to another interface?

Of course, the chance of that happening is very slim, I'm still just curious of how that would be handled.

I am doing something like this on my Linux box. I have code looking for the PD from the NS, and I add a host address on the end. Then I do a IP add command on the linux box. So the Prefix can change but the host address will always be the same.


Clever_Proxy
Premium
join:2004-05-14
Villa Park, IL

That's a really good idea. I assume this is just a bash script that grabs the prefix from the router and programs it into the interface config?



NetDog
Premium,VIP
join:2002-03-04
Parker, CO
kudos:79

said by Clever_Proxy:

That's a really good idea. I assume this is just a bash script that grabs the prefix from the router and programs it into the interface config?

In short yes.. but what I really want is to add an option the the networks config file that says something like this:

IPv6_postfix = 1:2:3:4

then when the ND comes in it adds that to the end of the prefix.

Right now my code does this every 30 minutes:

look at the IPv6 table

address_1 = (Static address 1:2:3:4 address)
address_2 = (EUI-64 address)

address_1_prefix = prefix of address_1
address_2_prefix = prefix of address_2

if Address_1_prefix =! Address_2_prefix
address_1 = address_2_prefix.IPv6_postfix
run command to add address_1