RE: Arp undo issue in all 2.4 and 2.6 kernel releases

From: Tim Wright
Date: Tue Nov 28 2006 - 16:58:27 EST



> -----Original Message-----
> From: Brian Haley [mailto:brian.haley@xxxxxx]
> Sent: Tuesday, November 28, 2006 1:48 PM
> To: Tim Wright
> Cc: Stephen Hemminger; linux-net@xxxxxxxxxxxxxxx
> Subject: Re: Arp undo issue in all 2.4 and 2.6 kernel releases
>
> Tim Wright wrote:
> > At the point where the system is responding, there should be no
> > interfaces with the given IP address and ifconfig confirms
> this. The
> > IP address is not associated with any interface and should not be
> > associated with the system either. The sequence of events
> is "bring up
> > the address on one interface, try to bring it up on another alias,
> > bring the address down". This isn't an issue of "replying
> to ARP out
> > the wrong interface", it is replying to arp requests when no
> > interfaces on the system have that IP address associated.
>
> At no point did you *delete* the address, it's still there.
> # ifconfig -a
>
> -Brian
>

Yes I did. One of the steps is 'ifconfig eth0:5 down'. That removes the
address. Here's a capture of running the commands on a CentOS 3 box. The
same things happen running 2.6.18. Please note that at the end NO
interfaces on the machine claim to own the 10.12.10.22 address, but the
machine still merrily responds to arp requests (I know I did the ping
locally, but if I do it from another machine, you can see the server
respond to the arp request in tcpdump/ethereal).

[root@nfstest root]# ifconfig
eth0 Link encap:Ethernet HWaddr 00:80:AD:72:3E:5A
inet addr:10.12.0.20 Bcast:10.12.255.255 Mask:255.255.0.0
inet6 addr: fe80::280:adff:fe72:3e5a/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:391347 errors:0 dropped:0 overruns:0 frame:0
TX packets:75 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:29269574 (27.9 Mb) TX bytes:6883 (6.7 Kb)
Interrupt:9 Base address:0x2400

lo Link encap:Local Loopback
inet addr:127.0.0.1 Mask:255.0.0.0
inet6 addr: ::1/128 Scope:Host
UP LOOPBACK RUNNING MTU:16436 Metric:1
RX packets:450 errors:0 dropped:0 overruns:0 frame:0
TX packets:450 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:89849 (87.7 Kb) TX bytes:89849 (87.7 Kb)

[root@nfstest root]# ping 10.12.0.22
PING 10.12.0.22 (10.12.0.22) 56(84) bytes of data.

--- 10.12.0.22 ping statistics ---
2 packets transmitted, 0 received, 100% packet loss, time 999ms

[root@nfstest root]# ifconfig eth0:5 10.12.0.22 netmask 255.255.0.0 up
[root@nfstest root]# ping 10.12.0.22
PING 10.12.0.22 (10.12.0.22) 56(84) bytes of data.
64 bytes from 10.12.0.22: icmp_seq=0 ttl=64 time=0.141 ms
64 bytes from 10.12.0.22: icmp_seq=1 ttl=64 time=0.064 ms

--- 10.12.0.22 ping statistics ---
2 packets transmitted, 2 received, 0% packet loss, time 999ms
rtt min/avg/max/mdev = 0.064/0.102/0.141/0.039 ms, pipe 2
[root@nfstest root]# ifconfig eth0:6 10.12.0.22 netmask 255.255.0.0 up
SIOCSIFFLAGS: Cannot assign requested address
[root@nfstest root]# ping 10.12.0.22
PING 10.12.0.22 (10.12.0.22) 56(84) bytes of data.
64 bytes from 10.12.0.22: icmp_seq=0 ttl=64 time=0.094 ms

--- 10.12.0.22 ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 0.094/0.094/0.094/0.000 ms, pipe 2
[root@nfstest root]# ifconfig
eth0 Link encap:Ethernet HWaddr 00:80:AD:72:3E:5A
inet addr:10.12.0.20 Bcast:10.12.255.255 Mask:255.255.0.0
inet6 addr: fe80::280:adff:fe72:3e5a/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:391665 errors:0 dropped:0 overruns:0 frame:0
TX packets:168 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:29294000 (27.9 Mb) TX bytes:20141 (19.6 Kb)
Interrupt:9 Base address:0x2400

eth0:5 Link encap:Ethernet HWaddr 00:80:AD:72:3E:5A
inet addr:10.12.0.22 Bcast:10.255.255.255 Mask:255.255.0.0
UP BROADCAST RUNNING MULTICAST MTU:1500 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:1000
RX bytes:0 (0.0 b) TX bytes:0 (0.0 b)
Interrupt:9 Base address:0x2400

lo Link encap:Local Loopback
inet addr:127.0.0.1 Mask:255.0.0.0
inet6 addr: ::1/128 Scope:Host
UP LOOPBACK RUNNING MTU:16436 Metric:1
RX packets:458 errors:0 dropped:0 overruns:0 frame:0
TX packets:458 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:90577 (88.4 Kb) TX bytes:90577 (88.4 Kb)

[root@nfstest root]# ifconfig eth0:5 down
[root@nfstest root]# ping 10.12.0.22
PING 10.12.0.22 (10.12.0.22) 56(84) bytes of data.
64 bytes from 10.12.0.22: icmp_seq=0 ttl=64 time=0.091 ms
64 bytes from 10.12.0.22: icmp_seq=1 ttl=64 time=0.080 ms

--- 10.12.0.22 ping statistics ---
2 packets transmitted, 2 received, 0% packet loss, time 1000ms
rtt min/avg/max/mdev = 0.080/0.085/0.091/0.010 ms, pipe 2
[root@nfstest root]# ifconfig
eth0 Link encap:Ethernet HWaddr 00:80:AD:72:3E:5A
inet addr:10.12.0.20 Bcast:10.12.255.255 Mask:255.255.0.0
inet6 addr: fe80::280:adff:fe72:3e5a/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:391809 errors:0 dropped:0 overruns:0 frame:0
TX packets:222 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:29305303 (27.9 Mb) TX bytes:28601 (27.9 Kb)
Interrupt:9 Base address:0x2400

lo Link encap:Local Loopback
inet addr:127.0.0.1 Mask:255.0.0.0
inet6 addr: ::1/128 Scope:Host
UP LOOPBACK RUNNING MTU:16436 Metric:1
RX packets:462 errors:0 dropped:0 overruns:0 frame:0
TX packets:462 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:90913 (88.7 Kb) TX bytes:90913 (88.7 Kb)

[root@nfstest root]# ifconfig -a
eth0 Link encap:Ethernet HWaddr 00:80:AD:72:3E:5A
inet addr:10.12.0.20 Bcast:10.12.255.255 Mask:255.255.0.0
inet6 addr: fe80::280:adff:fe72:3e5a/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:391836 errors:0 dropped:0 overruns:0 frame:0
TX packets:235 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:29307303 (27.9 Mb) TX bytes:31091 (30.3 Kb)
Interrupt:9 Base address:0x2400

eth1 Link encap:Ethernet HWaddr 00:80:AD:20:59:8B
BROADCAST MULTICAST MTU:1500 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:1000
RX bytes:0 (0.0 b) TX bytes:0 (0.0 b)
Interrupt:10 Base address:0x2800

eth2 Link encap:Ethernet HWaddr 00:01:02:C6:FE:C1
BROADCAST MULTICAST MTU:1500 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:1000
RX bytes:0 (0.0 b) TX bytes:0 (0.0 b)
Interrupt:9 Base address:0x2000

lo Link encap:Local Loopback
inet addr:127.0.0.1 Mask:255.0.0.0
inet6 addr: ::1/128 Scope:Host
UP LOOPBACK RUNNING MTU:16436 Metric:1
RX packets:462 errors:0 dropped:0 overruns:0 frame:0
TX packets:462 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:90913 (88.7 Kb) TX bytes:90913 (88.7 Kb)

sit0 Link encap:IPv6-in-IPv4
NOARP MTU:1480 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)
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