Multihoming confusion

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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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