For reasons not yet amenable to persuasion otherwise, a customer of our
ML2+OVS classic implemented OpenStack would like to map two floating IPs
pulled from two separate external network floating IP pools, to two
different vNICs on his instances.
The floating IP pools correspond to one pool routable from the external
Internet and another, RFC1918 pool routable from internal University
The tenant private networks are arranged as two RFC1918 VXLANs, each
with a router to one of the two external networks.
10.0.0.0/24 -> route to -> 126.96.36.199/23
10.0.16.0/24 -> route to -> 172.24.46.0/23
Mapping two floating IPs to instances isn't possible in Horizon, but is
possible from command-line. This doesn't immediately work, however, as
the return traffic from the instance needs to be sent back through the
correct router gateway interface and not the instance default gateway.
I'd initially thought this would be possible by placing a second routing
table on the instances to handle the return traffic;
debian@test1:/etc/iproute2$ less rt_tables
# reserved values
debian@test1:/etc/network$ less interfaces
# The loopback network interface
iface lo inet loopback
# The first vNIC, eth0
iface eth0 inet dhcp
# The second vNIC, eth1
iface eth1 inet static
post-up ip route add 10.0.16.0/24 dev eth1 src 10.0.16.11 table rt2
post-up ip route add default via 10.0.16.1 dev eth1 table rt2
post-up ip rule add from 10.0.16.11/32 table rt2
post-up ip rule add to 10.0.16.11/32 table rt2
And this works well for SSH and ICMP, but curiously not for HTTP traffic.
Requests to a web-server listening on all vNICs are sent but replies not
received when the requests are sent to the second mapped floating IP
(HTTP requests and replies work as expected when sent to the first
mapped floating IP). The requests are logged in both cases however, so
traffic is making it to the instance in both cases.
I'd say this is clearly an unusual (and possibly un-natural)
arrangement, but I was wondering whether anyone else on Operators had
come across a similar situation in trying to map floating IPs from two
different external networks to an instance?
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