Hello Operators,

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 networks.

The tenant private networks are arranged as two RFC1918 VXLANs, each with a router to one of the two external networks. -> route to -> -> route to ->

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
255     local
254     main
253     default
0       unspec
# local
#1      inr.ruhep
1 rt2

debian@test1:/etc/network$ less interfaces
# The loopback network interface
auto lo
iface lo inet loopback

# The first vNIC, eth0
auto eth0
iface eth0 inet dhcp

# The second vNIC, eth1
auto eth1
iface eth1 inet static
        post-up ip route add dev eth1 src table rt2
        post-up ip route add default via dev eth1 table rt2
        post-up ip rule add from table rt2
        post-up ip rule add to 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?

Kind regards,

Paul Browne

Paul Browne
Research Computing Platforms
University Information Services
Roger Needham Building
JJ Thompson Avenue
University of Cambridge
United Kingdom
E-Mail: pf...@cam.ac.uk
Tel: 0044-1223-46548

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