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Date: Fri, 25 Jan 2008 02:50:16 -0800
From: Andrew Morton <akpm@...ux-foundation.org>
To: netdev@...r.kernel.org
Cc: bugme-daemon@...zilla.kernel.org, bjorn@...k.no
Subject: Re: [Bugme-new] [Bug 9811] New: Loopback address to eth0 interface
changes scope permanently
> On Fri, 25 Jan 2008 02:04:04 -0800 (PST) bugme-daemon@...zilla.kernel.org wrote:
> http://bugzilla.kernel.org/show_bug.cgi?id=9811
>
> Summary: Loopback address to eth0 interface changes scope
> permanently
> Product: Networking
> Version: 2.5
> KernelVersion: 2.6.24-rc8
> Platform: All
> OS/Version: Linux
> Tree: Mainline
> Status: NEW
> Severity: normal
> Priority: P1
> Component: IPV4
> AssignedTo: shemminger@...ux-foundation.org
> ReportedBy: bjorn@...k.no
>
>
> Latest working kernel version: none
> Earliest failing kernel version: 2.6.18 (verified, but most likely "any")
> Distribution: Debian
> Hardware Environment:
> Software Environment:
> Problem Description:
>
> >From gary.manchon@...il.com :
>
> After a bad network interface configuration (ifconfig eth0 127.0.0.1),
> I cannot recover the network without rebooting the kernel.
>
> This is my working configuration :
>
> # ifconfig
> eth0 Link encap:Ethernet HWaddr 00:90:3E:1F:1C:17
> inet addr:192.168.240.195 Bcast:192.168.247.255 Mask:255.255.248.0
> UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
> RX packets:26 errors:0 dropped:0 overruns:0 frame:0
> TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
> collisions:0 txqueuelen:1000
> RX bytes:2633 (2.5 KiB) TX bytes:0 (0.0 B)
>
> lo Link encap:Local Loopback
> inet addr:127.0.0.1 Mask:255.0.0.0
> UP LOOPBACK RUNNING MTU:16436 Metric:1
> RX packets:0 errors:0 dropped:0 overruns:0 frame:0
> TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
> collisions:0 txqueuelen:0
> RX bytes:0 (0.0 B) TX bytes:0 (0.0 B)
>
> # route
> Kernel IP routing table
> Destination Gateway Genmask Flags Metric Ref Use Iface
> 192.168.240.0 * 255.255.248.0 U 0 0 0 eth0
> default 192.168.240.1 0.0.0.0 UG 0 0 0 eth0
>
> # ping -c 1 66.102.11.99
> PING 66.102.11.99 (66.102.11.99): 56 data bytes
> 64 bytes from 66.102.11.99: icmp_seq=0 ttl=63 time=4.5 ms
>
> --- 66.102.11.99 ping statistics ---
> 1 packets transmitted, 1 packets received, 0% packet loss
> round-trip min/avg/max = 4.5/4.5/4.5 ms
>
> Steps to reproduce:
>
> # ifconfig eth0 127.0.0.1
> # ifconfig eth0 192.168.240.195 netmask 255.255.248.0
> # route add default gw 192.168.240.1
>
>
> >From Bjørn Mork <bjorn@...k.no> :
>
> I suspect that the problem might be this code in net/ipv4/devinet.c ,
> which sets ifa_scope to RT_SCOPE_HOST if you configure a loopback
> address (127/8) on any interface. I guess it's there to protect us from
> sending packets with a loopback source address, which woulnd't look too
> good:
>
> static int inet_set_ifa(struct net_device *dev, struct in_ifaddr *ifa)
> {
> struct in_device *in_dev = __in_dev_get_rtnl(dev);
>
> ASSERT_RTNL();
>
> if (!in_dev) {
> inet_free_ifa(ifa);
> return -ENOBUFS;
> }
> ipv4_devconf_setall(in_dev);
> if (ifa->ifa_dev != in_dev) {
> BUG_TRAP(!ifa->ifa_dev);
> in_dev_hold(in_dev);
> ifa->ifa_dev = in_dev;
> }
> if (LOOPBACK(ifa->ifa_local))
> ifa->ifa_scope = RT_SCOPE_HOST;
> return inet_insert_ifa(ifa);
> }
>
>
>
> The real problem is that there's never anything resetting this scope if
> you change the address later. The attached patch fixes this.
>
>
> dhcp232:~# ip addr show dev eth0
> 2: eth0: <BROADCAST,MULTICAST,UP,10000> mtu 1500 qdisc pfifo_fast qlen 1000
> link/ether 00:aa:00:ff:00:ff brd ff:ff:ff:ff:ff:ff
> inet 192.168.3.232/24 brd 192.168.3.255 scope global eth0
> inet6 2001:16d8:ffb4:0:2aa:ff:feff:ff/64 scope global dynamic
> valid_lft 2591971sec preferred_lft 604771sec
> inet6 fe80::2aa:ff:feff:ff/64 scope link
> valid_lft forever preferred_lft forever
> dhcp232:~# ifconfig eth0 127.0.0.1
> dhcp232:~# ip addr show dev eth0
> 2: eth0: <BROADCAST,MULTICAST,UP,10000> mtu 1500 qdisc pfifo_fast qlen 1000
> link/ether 00:aa:00:ff:00:ff brd ff:ff:ff:ff:ff:ff
> inet 127.0.0.1/8 brd 127.255.255.255 scope host eth0
> inet6 2001:16d8:ffb4:0:2aa:ff:feff:ff/64 scope global dynamic
> valid_lft 2591951sec preferred_lft 604751sec
> inet6 fe80::2aa:ff:feff:ff/64 scope link
> valid_lft forever preferred_lft forever
> dhcp232:~# ifconfig eth0 192.168.3.232
> dhcp232:~# ip addr show dev eth0
> 2: eth0: <BROADCAST,MULTICAST,UP,10000> mtu 1500 qdisc pfifo_fast qlen 1000
> link/ether 00:aa:00:ff:00:ff brd ff:ff:ff:ff:ff:ff
> inet 192.168.3.232/24 brd 192.168.3.255 scope host eth0
> inet6 2001:16d8:ffb4:0:2aa:ff:feff:ff/64 scope global dynamic
> valid_lft 2591933sec preferred_lft 604733sec
> inet6 fe80::2aa:ff:feff:ff/64 scope link
> valid_lft forever preferred_lft forever
>
>
>
> Notice how the scope changes from "global" to "host" when configuring
> 127.0.0.1, and just never changes back. It will stay that way forever,
> or until something changes the scope or deletes the address.
>
> Deleting the addresss and re-adding it will work around the problem:
>
> dhcp232:~# ip addr del 192.168.3.232/24 dev eth0
> dhcp232:~# ifconfig eth0 192.168.3.232
> dhcp232:~# ip addr show dev eth0
> 2: eth0: <BROADCAST,MULTICAST,UP,10000> mtu 1500 qdisc pfifo_fast qlen 1000
> link/ether 00:aa:00:ff:00:ff brd ff:ff:ff:ff:ff:ff
> inet 192.168.3.232/24 brd 192.168.3.255 scope global eth0
> inet6 2001:16d8:ffb4:0:2aa:ff:feff:ff/64 scope global dynamic
> valid_lft 2591963sec preferred_lft 604763sec
> inet6 fe80::2aa:ff:feff:ff/64 scope link
> valid_lft forever preferred_lft forever
>
>
> Bjørn
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