The document discusses using BGP dynamic routing with Neutron to route cloud network traffic. It provides an overview of Neutron's BGP dynamic routing service and applications. Currently Neutron networks use static routing, but dynamic routing would allow routes to move between routers more easily. The document outlines how Neutron could insert routes into a routing protocol to advertise to infrastructure routers. Future applications discussed include routed network segments, L3 VPNs, and directly routible tenant networks.

1. BGP Dynamic Routing
and Neutron
Ryan Tidwell - HP
Jaume Devesa - Midokura
Vikram Choudhary - Huawei

2. Overview
• Routing Cloud Network Traffic
• Neutron BGP Dynamic Routing Service Overview
• Applications of BGP Dynamic Routing with Neutron
• Future Work
• Q&A

3. Solutions for Routing Cloud Traffic
• Neutron networks are typically stub networks with
default route and host routes statically defined for
outbound flows by Neutron
• Outbound gateway IP determined by reading
‘gateway_ip’ from the external network subnet
entity
• Next hop for inbound flows must be
communicated to infrastructure routers, but how?
• Options
• Static routing
• Dynamic routing

4. • Static routing requires manual
configuration of next-hops for each
tenant network prefix or floating IP
host route / prefix in upstream
infrastructure routers
• Floating IP’s either must be
confined to single L2 network, or
host routes must be configured
manually
• Operator intervention required
each time a router is created or
deleted
• Prefixes don’t move between
Neutron routers easily
Static Routing of Cloud Traffic

5. Dynamic Routing
• Operator configures routing
protocol amongst infrastructure
routers
• Make Neutron insert routes into
the routing protocol on subnet,
router, and floating IP CRUD
• Isolate Neutron L3 agent from
these changes, so use Neutron as
a BGP route server and peer it with
infrastructure routers
• Neutron will advertise routes to
peers, but does not learn from
peers

6. Why BGP?
• Separation between data plane and control plane
• Work with different AS
• Minimal topology to manage

7. Applications of Neutron BGP Dynamic
Routing
• Routed Model for Floating IP’s
• Unbind the floating range from the L2 network (see routed network segments)
• As floating IP’s become unbound from the L2 network, we can advertise a host route for a
floating IP as it moves across different L2 network segments.
• Directly Routable IPv4/IPv6 Tenant Networks
• Use BGP to advertise tenant prefixes for direct routing without floating IP’s or statically
routing tenant prefixes
• DVR
• Enable north-south DVR by advertising host routes with the compute node as the next-hop
• Presents some scaling challenges (large number of host routes), is route aggregation possible
and would it help?

8. Future Applications of Neutron BGP
Dynamic Routing
• Routed Network Segments
• https://review.openstack.org/#/c/225384/
• This spec is to support operators who want to be able to attach intances to the network using
an L3 domain as the identifier instead of an L2 network i.e. the traditional Neutron “network”
• Offers a way of using Neutron to model L3 networks decoupled from the L2 segments they
span
• Assigning a floating IP wouldn’t require a Neutron router. Use BGP to advertise the floating IP
• L3/BGP VPN (Potential Future Application)
• Advertise route distinguisher for an address scope to PE routers
• Not within scope for Mitaka, but is a potential enhancement
• Advertise Floating Range through a Neutron defined Gateway Router

9. Routed Model for Floating Range spanned in multiple L2 domains

10. Directly Routable Tenant Networks with Address Scopes
IPv6 networks don’ t need to be natted
Some small providers don’t want to use Floating IPs
Address Scopes will allow to define L3 routed domains instead of forcing NAT on tenant routers
(public access to tenant networks)
Subnet Pools allow to create non-overlapping Subnets
Address Scopes will group non-overlapping Subnet Pools.
BGP will automatically advertise new created subnets
External Gateway is the BGP peer

11. Routable Tenant Networks with Address Scopes

12. Advertise the Floating Range
With previous examples, cloud admin has to configure the Gateway Router to advertise Floating Range to ISP
or other Enterprise Routers
If Gateway Router belonged to Neutron model, we could associate the External Network to BGP speaker and
advertise it.
Some Neutron SDN controllers (like MidoNet) can implement the Dynamic Routing extension and advertise
the Floating Range(s)

13. Advertise Floating Range

14. DVR With BGP
• Each instance IP is advertised
as a host route with the
compute node IP on the
external network as the next-
hop
• External network does not need
to consume a routable prefix. It
can be treated as if it were a
link-local prefix.
• Large numbers of host routes
won’t necessarily scale nicely.
Is there a creative way to host
aggregate routes?

15. Architecture Overview

16. Sample Deployment
(simple)
• Entire cloud is treated as a
single autonomous system
• Operator network runs in
a separate autonomous
system
• eBGP peering with
operator network

17. Sample Deployment
(advanced)
• External network for each
rack
• Each rack is treated as an
autonomous system
• Infrastructure routers
redistribute Neutron
routes learned by BGP into
an IGP
• A single address scope
can be shared across
racks

18. Potential MPLS/BGP VPN Application

19. Why MPLS/BGP VPN
- Omni presence of MPLS technology.
- Almost all the backbone routers understands MPLS.
- QoS guarantee
- Easier to manage
- Scales reasonably

20. L3 VPN Support
• While not the target use case, L3VPN is important to consider.
• At the moment this effort is focused primarily on building the mechanism by which Neutron can
“speak” BGP and advertise routers to neighbors
• In future cycles we will be looking to add L3VPN support and see how similar work in this arena
can be discussed, combined and move forward.

21. Future Work
• L3 VPN
• BGP-MPLS for tenant-only address scopes
• OSPF and IS-IS are very different protocols from BGP, and we don’t think we can leverage any
work done on BGP.
• Route policing support

22. Resources
• https://review.openstack.org/#/c/196452/
•
https://review.openstack.org/#/q/status:open+project:openstack/neutron+branch:master+topic
:bp/bgp-dynamic-routing,n,z
• http://ryu-zhdoc.readthedocs.org/en/latest/library_bgp_speaker.html
• http://docs.openstack.org/developer/networking-bgpvpn/
• https://review.openstack.org/#/c/225384

23. How To Get Involved
• We’re here at the summit, feel free to corner us!
• We’d love to hear from operators, your feedback on direction and utility is greatly valued
• Reviews
• https://review.openstack.org/#/q/status:open+project:openstack/neutron+branch:master+to
pic:bp/bgp-dynamic-routing,n,z
• Code reviews are greatly valued
• Let us know if you’re interested in contributing code!

24. Q&A