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Re: [PATCH] IPv6: (5/5+1) Autoconfig link-local addr to IPv6 tunnels

To: Pekka Savola <pekkas@xxxxxxxxxx>
Subject: Re: [PATCH] IPv6: (5/5+1) Autoconfig link-local addr to IPv6 tunnels
From: Ville Nuorvala <vnuorval@xxxxxxxxxx>
Date: Tue, 2 Sep 2003 19:59:07 +0300 (EEST)
Cc: "David S. Miller" <davem@xxxxxxxxxx>, <yoshfuji@xxxxxxxxxxxxxx>, <usagi-core@xxxxxxxxxxxxxx>, <netdev@xxxxxxxxxxx>
In-reply-to: <Pine.LNX.4.44.0309021735350.4244-100000@netcore.fi>
Sender: netdev-bounce@xxxxxxxxxxx
On Tue, 2 Sep 2003, Pekka Savola wrote:

> Two comments:
>
> +       /* try to inherit EUI64 from another device */
> +       for (dev = dev_base; dev; dev = dev->next) {
> +               if (!ipv6_generate_eui64(addr.s6_addr + 8, dev)) {
> +                       addrconf_add_linklocal(idev, &addr);
> +                       return;
> +
>
> ==> does this really inherit _EUI64_, *or* MAC address (or something like
> it) to derive an EUI64?  Note that there is a significant difference when
> you've configured manually e.g. 3ffe:ffff:f00:ba::1 on a device, and the
> case when you've auto-configured the interface identifier from the MAC
> address of the device.

ipv6_generate_eui64() derives the interface identifier from the MAC
address on ARPHRD_{ETHER,FDDI,IEEE802_TR,ARCNET} interfaces, but doesn't
do anything for other types of devices

> ==> my question is: as the former method to steal an EUI64 should succeed
> pretty much always, is it useful to add basically dead code which never
> gets executed here?  I certainly can't think of any scenario where you'd
> have no interface to steal the MAC address/EUI64 from and you'd have to
> fall back to random identifiers?

If the node doesn't have an Ethernet (etc.) NIC it won't get a valid
identifier from ipv6_generate_eui64() and has to resort to something
else, for example generating a random address.

An alternative would be to use ipv6_inherit_eui64(), which just copies the
64-bit suffix from the first link-local address it can find. This includes
both manually and auto-configured addresses, which means the risk of
duplicate addresses might be (I assume) greater than in the random address
case.

Regards,
Ville
--
Ville Nuorvala
Research Assistant, Institute of Digital Communications,
Helsinki University of Technology
email: vnuorval@xxxxxxxxxx, phone: +358 (0)9 451 5257




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