On Sun, Jan 31, 2010 at 12:05 PM, wrote:
> Hi every
>
> I am changing the ISP from aaa.bbb.243.160/27 to ccc.ddd.206.128/27.
> In order to provide seamless service to our customers I made the hosts
> concerned multihomed, i.e. I added them a logical interface on the new
> subnet. I did not introduce a additional NIC into the hosts.
> Then, I changed the default route on the hosts to the new network.
>
> e.g in one host concerned you will see
>
> myhost:~ # ifconfig
> eth0 Link encap:Ethernet HWaddr 00:80:AD:B8:39:C3
> inet addr:ccc.ddd.206.132 Bcast:aaa.bbb.243.191
> Mask:255.255.255.224
> inet6 addr: fe80::80:adb8:39c3/10 Scope:Link
> inet6 addr: fe80::280:adff:feb8:39c3/10 Scope:Link
> UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
> RX packets:2733080 errors:0 dropped:0 overruns:0 frame:0
> TX packets:2494806 errors:0 dropped:0 overruns:0 carrier:0
> collisions:119322 txqueuelen:100
> RX bytes:791914000 (755.2 Mb) TX bytes:579375282 (552.5 Mb)
> Interrupt:9 Base address:0xf000
>
> eth0:1 Link encap:Ethernet HWaddr 00:80:AD:B8:39:C3
> inet addr:192.168.97.164 Bcast:192.168.97.255 Mask:255.255.255.0
> UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
> Interrupt:9 Base address:0xf000
>
> eth0:2 Link encap:Ethernet HWaddr 00:80:AD:B8:39:C3
> inet addr:aaa.bbb.243.164 Bcast:ccc.ddd.206.159
> Mask:255.255.255.224
> UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
> Interrupt:9 Base address:0xf000
>
> 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:372918 errors:0 dropped:0 overruns:0 frame:0
> TX packets:372918 errors:0 dropped:0 overruns:0 carrier:0
> collisions:0 txqueuelen:0
> RX bytes:92340116 (88.0 Mb) TX bytes:92340116 (88.0 Mb)
>
> myhost:~ #
>
> and
>
> myhost:~ # route -n
> Kernel IP routing table
> Destination Gateway Genmask Flags Metric Ref Use Iface
> aaa.bbb.243.160 0.0.0.0 255.255.255.224 U 0 0 0 eth0
> ccc.ddd.206.128 0.0.0.0 255.255.255.224 U 0 0 0 eth0
> 192.168.97.0 0.0.0.0 255.255.255.0 U 0 0 0 eth0
> 0.0.0.0 ccc.ddd.206.129 0.0.0.0 UG 0 0 0 eth0
> myhost:~ #
>
> NOTE: this multihoming has nothing to do with additional security or
> performance.
>
> I did not install something with iproute2 or other routing enhancements.
>
> PROBLEM: the multihoming works only partially.
>
> if I invoke e.g. ping on http://iptools.com/ the ping reply does not come
> back to its origin. The echo request reaches my server, my server sends an
> echo reply, which never reaches the originator.
>
>
> myhost:~ # tcpdump -n ip proto \\icmp
> Kernel filter, protocol ALL, datagram packet socket
> tcpdump: listening on eth0
> 10:58:35.508765 74.52.9.36 > aaa.bbb.243.164: icmp: echo request (DF)
> 10:58:35.508765 aaa.bbb.243.164 > 74.52.9.36: icmp: echo reply (DF)
> 10:58:36.508765 74.52.9.36 > aaa.bbb.243.164: icmp: echo request (DF)
> 10:58:36.508765 aaa.bbb.243.164 > 74.52.9.36: icmp: echo reply (DF)
> 10:58:37.508765 74.52.9.36 > aaa.bbb.243.164: icmp: echo request (DF)
> 10:58:37.508765 aaa.bbb.243.164 > 74.52.9.36: icmp: echo reply (DF)
> 10:58:38.508765 74.52.9.36 > aaa.bbb.243.164: icmp: echo request (DF)
> 10:58:38.508765 aaa.bbb.243.164 > 74.52.9.36: icmp: echo reply (DF)
> 10:58:39.508765 74.52.9.36 > aaa.bbb.243.164: icmp: echo request (DF)
> 10:58:39.508765 aaa.bbb.243.164 > 74.52.9.36: icmp: echo reply (DF)
> ...
>
> on http://iptools.com/ :
> PING aaa.bbb.243.164 (aaa.bbb.243.164) 56(84) bytes of data.
>
> --- aaa.bbb.243.164 ping statistics ---
> 5 packets transmitted, 0 received, 100% packet loss, time 3999ms
>
>
>
> If, however, I ping the Host on the other (the new) network address from
> http://iptools.com/, the ping gets through:
>
>
> myhost:~ # tcpdump -n ip proto \\icmp
> Kernel filter, protocol ALL, datagram packet socket
> tcpdump: listening on eth0
> 11:23:04.117248 74.52.9.36 > ccc.ddd.206.132: icmp: echo request (DF)
> 11:23:04.117248 ccc.ddd.206.132 > 74.52.9.36: icmp: echo reply (DF)
> 11:23:05.117248 74.52.9.36 > ccc.ddd.206.132: icmp: echo request (DF)
> 11:23:05.117248 ccc.ddd.206.132 > 74.52.9.36: icmp: echo reply (DF)
> 11:23:06.117248 74.52.9.36 > ccc.ddd.206.132: icmp: echo request (DF)
> 11:23:06.117248 ccc.ddd.206.132 > 74.52.9.36: icmp: echo reply (DF)
> 11:23:07.117248 74.52.9.36 > ccc.ddd.206.132: icmp: echo request (DF)
> 11:23:07.117248 ccc.ddd.206.132 > 74.52.9.36: icmp: echo reply (DF)
> 11:23:08.117248 74.52.9.36 > ccc.ddd.206.132: icmp: echo request (DF)
> 11:23:08.117248 ccc.ddd.206.132 > 74.52.9.36: icmp: echo reply (DF)
>
> on http://iptools.com/
>
> PING ccc.ddd.206.132 (ccc.ddd.206.132) 56(84) byt