1. Ethane: Taking Control of the Enterprise
Authors: Martin Casado, Michael J. Freedman, Justin Pettit, Jianying Luo , Nick McKeown, Scott Shenker
Publisher: ACM SIGCOMM Conference - SIGCOMM , 2007
Presenter: 楊皓中
Date: 2013/10/09

2. Introduction
Enterprise networks are often large, run a wide variety of applications and protocols, and typically operate under strict reliability and security constraints; thus, they represent a challenging environment for network management.
Yet the current solutions are weak, making enterprise network management both expensive and error-prone.
62% of network downtime in multi-vendor networks comes from human-error
80% of IT budgets is spent on maintenance and operations .
How could we change the enterprise network architecture to make it more manageable?
Ethane

3. Ethane is built around three fundamental principles
The network should be governed by policies declared over high level names
Policy should determine the path that packets follow
The network should enforce a strong binding between a packet and its origin.
The loose binding between users and their traffic is a constant target for attacks in enterprise networks.
address是動態的變化的，很容易用來欺騙別人，所以我們需要一個strong的binding，binding 實體位置，這樣也可以達到一致性，也可以trace packet的來源。

4. Overview of ethane
It imposes this requirement through two main components.
Central Controller
containing the global network policy that determines the fate of all packets.
knows the global network topology and performs route computation for permitted flows.
Ethane Switches
Consisting of a simple flow table and a secure channel to the Controller
simply forward packets under the direction of the Controller.
When a packet arrives that is not in the flow table, they forward that packet to the Controller, along with information about which port the packet arrived on.

5. Ethane in use --the five basic activities
Registration
Bootstrapping
Authentication
Flow Setup
Forwarding
Switches bootstrap connectivity by creating a spanning tree rooted at the Controller.
As the spanning tree is being created, each switch authenticates with and creates a secure channel to the Controller.
Once a secure connection is established, the switches send link-state information to the Controller,
which aggregates this information to reconstruct the network topology.

6. Ethane in more detail—An Ethane Network

7. Ethane in more detail—Switch
Ethane Switch VS Ethernet switch
A wired Ethane Switch is like a simplified Ethernet switch.
An Ethane Switch doesn’t need to learn addresses, support VLANs, check for source-address spoofing, or keep flow-level statistics,maintain forwarding tables,run routing protocols such as OSPF, ISIS, and RIP.
the flow table can be several orders-of-magnitude smaller than the forwarding table in an equivalent Ethernet switch
Ethane不用去支援很多Ethernet switch有的功能
還有一點是，第3點，因為Rthernet會因為大量學習address使的forwarding table 很大
而__很小 所以可以坐在 On chip上

8. Ethane in more detail—Switch
Flow Table and Flow Entries
contain a Header (to match packets against), an Action (to tell the switch what to do with the packet), and Per-Flow Data.
Local Switch Manager
monitor link status
establish and maintain the secure channel to the Controller
two ways a Switch can talk to the Controller.
within the same broadcast domain
Using our modified Minimum Spanning Tree
secure channel stretching through these intermediate Switches all the way to the Controller.
not within the same broadcast domain
IP tunnel

9. Ethane in more detail—Controller
The Controller is the brain of the network and has many tasks

10. Ethane in more detail—Controller
Registration
All entities that are to be named by the network must be registered.
Authentication
a network could support multiple authentication methods
Tracking Bindings
One of Ethane’s most powerful features is that it can easily track all the bindings between names, addresses, and physical ports on the network.
Namespace Interface
it can make information available to network managers, auditors, or anyone else who seeks to understand who sent what packet and when.
Permission Check and Access Granting
Enforcing Resource Limits
Lightweight Directory Access Protocol
像是hosts authenticate by presenting registeredMAC addresses,while users authenticate through a web front-end to a Kerberos server.

11. Ethane in more detail—Handling Broadcast and Multicast
The Switch keeps a bitmap for each flow to indicate which ports the packets are to be sent to along the path.
Broadcast
a host is trying to find a server or an address. Controller can reply to a request without creating a new flow and broadcasting the traffic
ARP could generate a huge load for the Controller
ARP server
it should be possible to provide a direct way to query the network
可是如果只為了ARP 就多一個server，那其他協定不就也要增加?

12. Ethane in more detail—Replicating the controller Fault-Tolerance and Scalability
Multiple Controllers may be desirable to provide fault-tolerance or to scale to very large networks.
cold-standby approach
having no network binding state
The warm-standby approach
having network binding state
The fully-replicated approach

13. Ethane in more detail—Link Failures
When a link fails , the Switch removes all flow table entries tied to the failed port and sends its new link-state information to the Controller, and the Controller computes and installs a new path based on the new topology.

14. Ethane in more detail—Bootstrapping
When the network starts, the Switches must connect to and authenticate with the Controller
On startup, the network creates a minimum spanning tree with the Controller advertising itself as the root.
Each Switch has been configured with the Controller’s credentials
If a Switch finds a shorter path to the Controller, it attempts two way authentication with it before advertising that path as a valid route.

15. The POL-ETH policy language
multiple rules with conflicting actions may
be satisfied by the same flow. Conflicts are
resolved by assigning priorities based on
declaration order.

16. The POL-ETH policy language—Implementation
Creating a lookup table for all possible flows specified in the policy would be impractical.
Our Pol-Eth implementation combines compilation and just-in-time creation of search functions
have implemented a source-to-source compiler that generates C++ from a Pol- Eth policy file. The resulting source is then compiled and linked into the Ethane binary. As a consequence, policy changes currently require relinking the Controller. We are currently upgrading the policy compiler so that policy changes can be dynamically loaded at runtime.

17. Prototype and Deployment
At university , over 300 host , several hundred users.
Deployed a remote switch in private residence.
The whole network is managed by single PC-based Controller.
Includes 19 switches of three different types.
Ethane Wireless Access Point
wireless router(266MHz MIPS, 32MB RAM)
talks to the Controller using the native Linux TCP stack
Ethane 4-port Gigabit Ethernet Switch: Hardware Solution.
implemented on NetFPGA
4MB of SRAM for packet buffers and the flow table
Ethane 4-port Gigabit Ethernet Switch: Software Solution.
built a Switch from a regular desktop PC (1.6GHz Celeron CPU and 512MB of DRAM)

18. Prototype and Deployment
Controller
A standard Linux PC(1.6GHz Celeron CPU and 512MB of DRAM)
100MB/s Ethernet network
11 wired and 8 wireless Ethane switch
average of 120 hosts active in a 5-minute window

19. Performance and scalability--primary question
How many Controllers are needed for a network of a given size?
How big does the flow table need to be in the Switch?

20. Performance and scalability
we see new flow requests per second (Figure 5) with a peak of 750 flow requests per second. 9 Figure 6 shows how our Controller performs under load: for up to 11,000 flows per second—greater than the peak load we observed—flows were set up in less than 1.5 milliseconds in the worst case, and the CPU showed negligible load.
然後我們期待如果對這個設計最佳化，可以使每秒10000的這個數字可以增加。在這個想法下，也會去探討 有多少的host才能與這個load相稱

21. Performance and scalability—
Figure 7 : 8000 host
never exceeded 1,200 per second
across all nodes
Figure 8 : host
under 9,000 new flow-requests per second
suggest that a single Controller could
comfortably manage a network with over
20,000 hosts.

22. Performance and scalability—Performance During Failures
cold-standby failure recovery
we measured the completion time of 275 consecutive HTTP requests
我們目前適用cold-standby的方式來實做，測試275個連續的HTTP要求，在其中有幾次觀調constroller再打開。觀察他完成的時間， S—MS
因為使用cold所以還必須等他re-establish，用其他的方式會比較快。

23. Performance and scalability—Performance During Failures
Failures were simulated by physically unplugging a link
In all cases, the path reconverges in under 40ms, but a packet could be delayed up to a second while the Controller handles the flurry of requests.
再來failure真的模擬試拔掉一條link，如果拔掉的link他的使用率是很高的，娜controller就會變得很，史的效能下降。
已圖10為例，平均處理時間小於40ms，但如果controller在忙著大量著要求，那樣時間就會增加。
paper中也有提到，未來可以實做存另一條disjohn的path在switch上，如果fail了可以快速的回覆。

24. Performance and scalability—Flow Table Sizing
Auniversity sized network
flow table capable of holding 8K–16K entries. If we assume that each entry is 64B, such a table requires about 1MB of storage
A typical commercial enterprise Ethernet
switch today holds 1 million Ethernet addresses (6MBif hashing is used)
1 million IP addresses (4MB of TCAM),
1-2 million counters (8MB of fast SRAM)
several thousand ACLs (more TCAM).
the memory requirements of an Ethane Switch are quite modest in comparison to today’s Ethernet switches.

25. ETHANE’S SHORTCOMINGS
Broadcast and Service Discovery
on our network, Broadcast discovery protocols constituted over 90% of the flows
Application-layer routing
For example, if A is allowed to talk to B but not C, and if B can talk to C, then B can relay messages from A to C
Knowing what the user is doing.
Ethane’s policy assumes that the transport port numbers indicate what the user is doing: port 80 means HTTP, port 25 is SMTP, and so on.
Spoofing Ethernet addresses
If a user spoofs a MAC address, it might be possible to fool Ethane into delivering packets to an end-host
做特定的事 會經過特定的port