Re: Multihoming confusion

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On Sun, Jan 31, 2010 at 12:05 PM,  <[email protected]> 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) 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?
>

You need to correct the routing, see
http://tldp.org/HOWTO/Adv-Routing-HOWTO/lartc.rpdb.multiple-links.html

//HW

> Thanks for any hints.
>
> suomi
>
>
>
>
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