Subject: [dhcwg] Questions for DHCP assign two ipv4 address to one interface

From: Hui Deng <[email-masked]>
Date: Thu, 23 Apr 2009 00:31:11 +0800

Dear all

May I consult whether one interface of DHCP client can get two ipv4
addresses from DHCP server?
furthermore could get two default gateway?

What we normally do is manual configure two ipv4 addressesfor 1 interface.
then manual configure static routing for each of them, it works with complexity.

Many thanks for your help
Best regards,

-Hui

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From: Ted Lemon <[email-masked]>
Date: Wed, 22 Apr 2009 11:47:45 -0500

> furthermore could get two default gateway?

Not really.   You can do two separate DHCP transactions with different  
client identifiers, on the same interface, but I would expect you to  
get the same gateway IP address in both replies.   Of course you would  
get two IP addresses, but I don't really see what good it would do.

---

From: Hui Deng <[email-masked]>
Date: Thu, 23 Apr 2009 00:57:51 +0800

thanks for explanation.
is this client identifier a mac address?

-Hui

2009/4/23 Ted Lemon <[email-masked]>:
> client identifiers, on the same interface, but I would expect you to get the
> same gateway IP address in both replies.   Of course you would get two IP
> addresses, but I don't really see what good it would do.
>
>

---

From: Ted Lemon <[email-masked]>
Date: Wed, 22 Apr 2009 12:05:16 -0500

> is this client identifier a mac address?

No, don't mess with the mac address - just change the dhcp client  
identifier option that you send.   The DHCP server is supposed to  
treat two DHCP messages with different client identifier options as if  
they come from two different DHCP clients.   It's possible that some  
DHCP server might key only on the Mac address, but in that case it's  
not really a DHCP server, because it's not following the protocol  
specification.

---

From: Ralph Droms <[email-masked]>
Date: Wed, 22 Apr 2009 14:59:08 -0400

The fundamental idea in DHCP (IPv4) is that each interface gets only  
one IP address.  As Ted suggests, it's possible for one physical host  
to get two IPv4 addresses by spoofing the idea of two different hosts,  
but the server won't have any notion that the two addresses have been  
assigned to a single physical host.

- Ralph

On Apr 22, 2009, at 1:05 PM 4/22/09, Ted Lemon wrote:

> treat two DHCP messages with different client identifier options as  
> if they come from two different DHCP clients.   It's possible that  
> some DHCP server might key only on the Mac address, but in that case  
> it's not really a DHCP server, because it's not following the  
> protocol specification.
>
> _______________________________________________
> dhcwg mailing list
> [email-masked]
> https://www.ietf.org/mailman/listinfo/dhcwg

---

From: "Bernie Volz (volz)" <[email-masked]>
Date: Wed, 22 Apr 2009 16:18:38 -0400

Folks ... Let's not forget Ted and Bill's RFC on this topic - RFC 4361,
Node-specific Client Identifiers for Dynamic Host Configuration Protocol
Version Four (DHCPv4). This RFC extends the use of the DHCPv6 DUID and
identity association concept to DHCPv4 and would be the best way to
accomplish getting multiple leases for a single client on a single
interface.

This is done by using the Client Identifier option (61):

       Code  Len  Type  IAID                DUID
       +----+----+-----+----+----+----+----+----+----+---
       | 61 | n  | 255 | i1 | i2 | i3 | i4 | d1 | d2 |...
       +----+----+-----+----+----+----+----+----+----+---

Then, by varying the IAID value, a single client can get multiple leases
with the same DUID (whether on a single or multiple interfaces). The
other advantage of this is the DNS updates should work correctly (at
least for those servers that understand this format of the client
identifier and use just the DUID when doing DNS updates).

- Bernie

-----Original Message-----
From: [email-masked] [mailto:[email-masked]] On Behalf
Of Ralph Droms (rdroms)
Sent: Wednesday, April 22, 2009 2:59 PM
To: Hui Deng
Cc: dhc WG
Subject: Re: [dhcwg] Questions for DHCP assign two ipv4 address to
oneinterface

- Ralph

---

From: Hui Deng <[email-masked]>
Date: Thu, 23 Apr 2009 20:52:55 +0800

Thanks Ted, Ralph and Bernie,

I guess it has been sufficient discussed.

the reason I asked this question is that mobile user is really using
multiple different ip address es for their different APN
communication, it seems workable for only 1 interface.

Anyhow, some of their address assignment is not based on DHCP but PDP context.
I guess that application may have diffculty to know which source
address is going to use.

Thanks again.

-Hui

---

From: <[email-masked]>
Date: Thu, 23 Apr 2009 14:57:45 +0200

Hui,

In the context of 3GPP networks which use APNs, each PDP connection (or PDN
bearer) can be viewed as a separate PtP connection between the host and the
GGSN. Hence it is possible to assign unique IPv4 addresses.
And I don't see any reason why you could not use DHCP to assign an address
for each PDP context. AFAIK, DHCP is a mechanism for assigning addresses to
PDP contexts. 

-Raj

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From: Hui Deng <[email-masked]>
Date: Thu, 23 Apr 2009 22:39:34 +0800

Raj

Good to discuss here, the scenario like this, one interface request
two PDP contexts to
two different LMA (let's use IETF word here, other than PDN GW), this
interface get two different IP addresses from two different DHCP
Servers, based on DHC WG's view, it is hard to implement,RFC 4361 may
do that.

but my problem with this, when the application like IE would like to
choose which source address to use, it will be the issue, since both
LMA has non-wap website connection.

thanks for the discussion

-Hui

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From: Behcet Sarikaya <[email-masked]>
Date: Thu, 23 Apr 2009 16:13:42 -0700 (PDT)

Hi Hui,
  Client ID or DUID is not a MAC address. It is host id, something like IMEI.
I think in DHCP IAID comes closer to MAC address.

Regards,

Behcet

________________________________
From: Hui Deng <[email-masked]>
To: Ted Lemon <[email-masked]>
Cc: dhc WG <[email-masked]>
Sent: Wednesday, April 22, 2009 11:57:51 AM
Subject: Re: [dhcwg] Questions for DHCP assign two ipv4 address to one interface

thanks for explanation.

-Hui