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List: dhcp-users
Subject: Interface Discover issue in ISC DHCP 4.1.0
From: Yong Bo Hu <huyongbo () cn ! ibm ! com>
Date: 2009-12-23 2:24:14
Message-ID: OF7D169A9C.BC87DF2C-ON48257694.0026D99B-48257695.000D2D1B () cn ! ibm ! com
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[Attachment #2 (multipart/alternative)]
Not sure whether it's fine to send this there.
The scenario:
Interface ETH0, has and only has IPv4:192.168.1.2 and IPv6 aaaa::cccc. Now
the IPv4 address is down, and the IPv6 address is up. And ranges of
192.168.1.0 and aaaa::/64 are configured. Next start the DHCP server with
IPv6(-6), the result is the ETH0 is skipped with no message in the log
about this interface. If the IPv4 is up, the ETH0 can be listened.
After debug, I locate the code in discover.c:.
/* Skip non broadcast interfaces (plus loopback and
point-to-point in case an OS incorrectly marks them
as broadcast). Also skip down interfaces unless we're:
trying to get a list of configurable interfaces. */
if (((!(info.flags & IFF_BROADCAST) ||
info.flags & IFF_LOOPBACK ||)
info.flags & IFF_POINTOPOINT) && !tmp) ||
(!(info.flags & IFF_UP) &&
state != DISCOVER_UNCONFIGURED))
continue;
On the surface, the interface can be listened depending on the state of
IPv4 address when starting IPv6 DHCP, but it shouldn't. The key point here
is the IFF_BROADCAST flag, for ordinary IPv4 address, it's broadcast
address valid, but for IPv6, which has not broadcast, but has multicast
(IFF_MULTICAST), so i think it would need to differentiate the IPv4 and
IPv6 when to check which interface needs to skip.
Best&Regards
Andy
[Attachment #5 (text/html)]
<html><body>
<p>Not sure whether it's fine to send this there.<br>
<br>
The scenario:<br>
Interface ETH0, has and only has IPv4:192.168.1.2 and IPv6 aaaa::cccc. Now the IPv4 \
address is down, and the IPv6 address is up. And ranges of 192.168.1.0 and aaaa::/64 \
are configured. Next start the DHCP server with IPv6(-6), the result is the ETH0 is \
skipped with no message in the log about this interface. If the IPv4 is up, the \
ETH0 can be listened.<br> <br>
After debug, I locate the code in discover.c:<br>
<br>
/* Skip non broadcast interfaces (plus loopback and<br>
point-to-point in case an OS incorrectly marks them<br>
as broadcast). Also skip down interfaces unless we're<br>
trying to get a list of configurable interfaces. */<br>
if (((!(info.flags & IFF_BROADCAST) ||<br>
info.flags & IFF_LOOPBACK ||<br>
info.flags & IFF_POINTOPOINT) && !tmp) ||<br>
(!(info.flags & IFF_UP) &&<br>
state != DISCOVER_UNCONFIGURED))<br>
continue;<br>
<br>
On the surface, the interface can be listened depending on the state of IPv4 address \
when starting IPv6 DHCP, but it shouldn't. The key point here is the IFF_BROADCAST \
flag, for ordinary IPv4 address, it's broadcast address valid, but for IPv6, which \
has not broadcast, but has multicast (IFF_MULTICAST), so i think it would need to \
differentiate the IPv4 and IPv6 when to check which interface needs to skip.<br> <br>
Best&Regards<br>
Andy</body></html>
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