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) bytes of data.
64 bytes from ccc.ddd.206.132: icmp_seq=1 ttl=245 time=132 ms
64 bytes from ccc.ddd.206.132: icmp_seq=2 ttl=245 time=132 ms
64 bytes from ccc.ddd.206.132: icmp_seq=3 ttl=245 time=133 ms
64 bytes from ccc.ddd.206.132: icmp_seq=4 ttl=245 time=132 ms
64 bytes from ccc.ddd.206.132: icmp_seq=5 ttl=245 time=132 ms
--- ccc.ddd.206.132 ping statistics ---
5 packets transmitted, 5 received, 0% packet loss, time 4000ms
rtt min/avg/max/mdev = 132.915/132.980/133.114/0.405 m
If I ping the iptools.com host from my host:
myhost:~ # ping 74.52.9.36
PING 74.52.9.36 (74.52.9.36): 56 data bytes
64 bytes from 74.52.9.36: icmp_seq=0 ttl=54 time=134.925 ms
64 bytes from 74.52.9.36: icmp_seq=1 ttl=54 time=133.172 ms
64 bytes from 74.52.9.36: icmp_seq=2 ttl=54 time=133.426 ms
64 bytes from 74.52.9.36: icmp_seq=3 ttl=54 time=133.735 ms
64 bytes from 74.52.9.36: icmp_seq=4 ttl=54 time=133.503 ms
--- 74.52.9.36 ping statistics ---
5 packets transmitted, 5 packets received, 0% packet loss
round-trip min/avg/max = 133.172/133.752/134.925 ms
myhost:~ #
Summary: If, on my host, a service is called for on the old
(aaa.bbb.243.160/27) network, it is not properly answered on the new
network (ccc.ddd.206.128/27).
I also tried to enable IP forwarding on this host
myhost:~ # !493
echo "1" > /proc/sys/net/ipv4/ip_forward
myhost:~ # cat /proc/sys/net/ipv4/ip_forward
1
myhost:~ #
but this did not change anything either.
Furthermore, I was informed on my googling around, that IP forwarding must
not be enabled on a multihomed host.
What did I miss?
Thanks for any hints.
suomi
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