Generic Fault-avoidance Routing Protocol for Data Center Networks
draft-sl-rtgwg-far-dcn-00
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Authors | Bin Liu , Yantao Sun , Jing Cheng , Yichen Zhang | ||
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draft-sl-rtgwg-far-dcn-00
Routing Area Working Group Bin Liu Internet-Draft ZTE Inc. Intended status: Informational Yantao Sun Expires: June 22, 2014 Jing Cheng Yichen Zhang Beijing Jiaotong University December 19, 2013 Generic Fault-avoidance Routing Protocol for Data Center Networks draft-sl-rtgwg-far-dcn-00 Abstract This draft proposed a generic routing method and protocol for a regular data center network, named as the fault-avoidance routing (FAR) protocol. FAR protocol provides a generic routing method for all kinds of network architectures that are proposed for large-scale cloud data centers over the past few years. FAR protocol is well designed to fully leverage the regularity in the topology and compute its routing table in a simple way. Fat-tree is taken as an example architecture to illuminate how to apply FAR protocol in this draft. Status of This Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on June 22, 2014. Copyright Notice Copyright (c) 2013 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of Bin Liu, et al. Expires June 22, 2014 [Page 1] Internet-Draft FAR for DCN December 2013 publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1. Acronyms & Definitions . . . . . . . . . . . . . . . . . 3 2. Conventions used in this document . . . . . . . . . . . . . . 4 3. Problem Statement . . . . . . . . . . . . . . . . . . . . . 4 3.1. The Impact of Large-scale Networks on Route Calculation . 4 3.2. Network Addressing Issues . . . . . . . . . . . . . . . . 5 3.3. Big Routing Table Issues . . . . . . . . . . . . . . . . 5 3.4. Adaptivity Issues for Routing Algorithms . . . . . . . . 6 3.5. Virtual Machine Migration Issues . . . . . . . . . . . . 6 4. The FAR Framework . . . . . . . . . . . . . . . . . . . . . . 6 5. Data Format . . . . . . . . . . . . . . . . . . . . . . . . . 7 5.1. Data Tables . . . . . . . . . . . . . . . . . . . . . . . 7 5.2. Messages . . . . . . . . . . . . . . . . . . . . . . . . 10 6. FAR Modules . . . . . . . . . . . . . . . . . . . . . . . . . 14 6.1. Neighbor & Link Detection Module(M1) . . . . . . . . . . 14 6.2. Device Learning Module(M2) . . . . . . . . . . . . . . . 14 6.3. Invisible Neighbor & Link Failure Inferring Module(M3) . 15 6.4. Link Failure Learning Module(M4) . . . . . . . . . . . . 15 6.5. BRT Building Module(M5) . . . . . . . . . . . . . . . . . 15 6.6. NRT Building Module(M6) . . . . . . . . . . . . . . . . . 15 6.7. Routing Table Lookup(M7) . . . . . . . . . . . . . . . . 16 7. Application Example . . . . . . . . . . . . . . . . . . . . . 16 7.1. BRT Building Procedure . . . . . . . . . . . . . . . . . 18 7.2. NRT Building Procedure . . . . . . . . . . . . . . . . . 18 7.2.1. Single Link Failure . . . . . . . . . . . . . . . . . 19 7.2.2. A Group of Link Failures . . . . . . . . . . . . . . 20 7.2.3. Node Failures . . . . . . . . . . . . . . . . . . . . 20 7.3. Routing Procedure . . . . . . . . . . . . . . . . . . . . 21 8. Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . 22 9. Reference . . . . . . . . . . . . . . . . . . . . . . . . . . 23 10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 23 11. Security Considerations . . . . . . . . . . . . . . . . . . . 23 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 23 Bin Liu, et al. Expires June 22, 2014 [Page 2] Internet-Draft FAR for DCN December 2013 1. Introduction In recent years, with the rapid development of cloud computing technologies, the widely deployed cloud services, such as Amazon EC2 and Google search, bring about huge challenges to data center networking (DCN). Today!_s cloud data centers (DCs) require large- scale networks with higher internal bandwidth and lower transfer delay, but conventional networks cannot meet such requirements due to limitations in their network architecture. To satisfy the requirements of cloud computing services, many new network architectures have been proposed for data centers, such as Fat-tree, MatrixDCN, and BCube. These new architectures can support non- blocking large-scale datacenter networks with more than tens of thousands of physical servers. Generic routing protocols such as OSPF and IS-IS cannot be scaled to support a very large-scale datacenter network because of the problems of network convergence and PDU overhead. For each type of architecture, researchers designed a routing algorithm according to the features of its topology. Because those routing algorithms have great difference and bad compatibility with each other, it is very difficult to develop a routing protocol for network routers supporting multiple routing algorithms. Furthermore, the fault tolerances in those routing algorithms are very complicated and have low efficiency. This draft proposed a generic routing method and protocol, fault- avoidance routing (FAR) protocol, for DCNs. This method leverages the regularity in the topologies of data center networks to simplify routing learning and speed up the query of routing tables. This routing method has good fault tolerance and can be applied to any DCN with a regular topology. 1.1. Acronyms & Definitions DCN - Data Center Network FAR - Fault-avoidance Routing BRT - Basic Routing Table NRT - Negative Routing Table NDT - Neighbor Devices Table ADT - All Devices Table LFT - Link failure Table Bin Liu, et al. Expires June 22, 2014 [Page 3] Internet-Draft FAR for DCN December 2013 DA - Device Announcement LFA - Link Failure Announcement DLR¨C Device and Link Request IP - Internet Protocol UDP - User Datagram Protocol 2. Conventions used in this document The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT","SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC-2119 [RFC2119]. In this document, these words will appear with that interpretation only when in ALL CAPS. Lower case uses of these words are not to be interpreted as carrying RFC-2119 significance. 3. Problem Statement The problem intended to be addressed by FAR is proposed in this section. The expansion of Cloud data center networks has brought great challenges to the existing routing technologies. FAR mainly solves a series of routing problems faced by large-scale data center network. 3.1. The Impact of Large-scale Networks on Route Calculation In a large-scale cloud data center network, there may be thousands of routers. Running OSPF and other routing protocols in such network will encounter these two questions: a) Network convergence time is too long, which will take a long time for creating and updating routes. The response to network failures may not be timely; b) a large number of routing protocol packets need to be sent. The routing information consumes a lot of network bandwidth and CPU resources, which easily leads to packet loss and makes the problem (a) more prominent. In order to solve these problems, the common practice is partitioning the large network into some small areas, where the route calculation runs independently within different areas. But nowadays the cloud data centers typically require very large internal bandwidth. To meet this requirement, a large number of parallel equivalent links are deployed in the network, such as the Fat-tree network architecture. Partitioning the network will affect the utilization of routing algorithm on equivalent multi-path and reduce internal network bandwidth. Bin Liu, et al. Expires June 22, 2014 [Page 4] Internet-Draft FAR for DCN December 2013 In the FAR routing calculation process, a Basic Routing Table (BRT) is built on local network topology leveraging the regularity of the network topologies.In addition to BRT, FAR also built a Negative Routing Table (NRT). FAR gradually builds NRT in the process of learning network link failure information, which does not require learning the complete network fault information. FAR does not need to wait for the completion of the network convergence in the process of building these two tables. It avoids the problem of excessive network convergence in the route calculation process. In addition, FAR only needs to exchange a small amount of link change information between routers, and consumes less network bandwidth. 3.2. Network Addressing Issues Routers typically configure multiple network interfaces, each connected to a subnet. OSPF and other routing algorithm require each interface of the router must be configured with an IP address. A large-scale data center network may contain thousands of routers. Tens of thousands of IP addresses may be needed to configure for each router with dozens of network interface. It will be a very complex issue to configure and manage a large number of network interfaces. Network maintenance is costly and error-prone. It will be difficult to troubleshoot the problems. In FAR, the device position information is encoded in the IP address of the router. Each router only needs to be assigned a unique IP address according its location, which greatly solves complex network addressing issues in large-scale network. 3.3. Big Routing Table Issues There are a large number of subnets in the large-scale data center network. Routers may build a routing entry for each subnet, and therefore the size of the routing tables on each router may be very large. It will increase equipment cost and reduce the querying speed of the routing table. FAR uses two measures to reduce the size of the routing tables: a) Builds a BRT on the regularity of the network topologies; b) introduces a new routing table, i.e. a NRT. In this way FAR can reduce the size of routing tables to only a few dozen routing entries. Bin Liu, et al. Expires June 22, 2014 [Page 5] Internet-Draft FAR for DCN December 2013 3.4. Adaptivity Issues for Routing Algorithms To implement efficient routing in large-scale datacenters, besides FAR, some other routing methods are proposed for some specific network architectures, such as Fat-tree and BCube. These routing methods have great difference and bad compatibility with conventional routing method and between each other on the ideas of design and implementation, which brings big troubles to network equipment providers to develop new routers supporting various new routing methods. FAR is a generic routing method. With slight modification, FAR method can be applied to most of regular datacenter networks. Furthermore, the structure of routing tables and querying a routing table in FAR are the same as conventional routing method. If FAR is adopted, the workload of developing a new type of router will be greatly decreased. 3.5. Virtual Machine Migration Issues Supporting VM migration is very important for cloud datacenter networks, but to support layer-3 routing, routing methods including OSPF and FAR require limiting VM migration within a subnet. For this paradox, the mainstream methods still run layer-3 routing on routers or switches, but transmit packets encapsulated by IPinIP or MACinIP between hosts by tunnels passing through network to the destination access switch, then extract original packet out and send it to the destination host. By means of the methods above, FAR can be applied to Fat-tree, MatrixDCN or BCube networks with supporting VM migration in entire network. 4. The FAR Framework FAR requires that a DCN has a regular topology, and network devices, including routers, switches, and servers, are assigned IP addresses according to their locations in the network. In other word, we can locate a device in the network according to its IP address. FAR is a distributed routing method. To support FAR, each router should be deployed a routing module that implement the FAR algorithm. FAR algorithm is composed of three parts, i.e., link-state learning, routing table building and routing table querying, as shown in Fig. 1. Bin Liu, et al. Expires June 22, 2014 [Page 6] Internet-Draft FAR for DCN December 2013 Link-state Learning |Routing Table | Routing Table | Building | | Querying +--------+ /---------------\ | +--------+ | Packets |2 Device|<--| 1 Neighbor & |----->| 5 BRT \ | |Learning| | Link Detection| | |Building|\ | | +--------+ \---------------/ | +--------+ \ | \|/ | | | \ |+--------------+ | | | /|| 7 Querying | \|/ \|/ | / || Routing Table| +-----------------------+| / |+--------------+ |3 Invisible Neighbor & || / | |Link Failure Inferring || +--------- | +-----------------------+|/| 6 NRT | | | / |Building| | \|/ /| +--------+ | +--------------+ / | | |4 Link Failure| / | | | Learning | | | +--------------+ | | | | Figure 1: The FAR framework Link-state learning is responsible for a router to detect the states of its connected links and learn the states of all the other links in the entire network. The second part builds two routing tables, a basic routing table (BRT) and an negative routing table (NRT), according to the learned link states in the first part. The third part queries the BRT and the NRT to decide a next forwarding hop for arrived packets. 5. Data Format 5.1. Data Tables Some data tables are maintained on each router in FAR. They are: Neighbor Device Table (NDT): To store neighbor routers and related links. All Devices Table (ADT): To store all routers in the entire network. Link Failures Table (LFT): To store all link failures in the entire network. Basic Routing Table (BRT): To store the candidate routes. Bin Liu, et al. Expires June 22, 2014 [Page 7] Internet-Draft FAR for DCN December 2013 Negative Routing Table(NRT): To store the avoiding routes. The format of NDT ---------------------------------------------------------- Device ID | Device IP | Port ID | Link State | Update Time ---------------------------------------------------------- Device ID: The ID of a neighbor router. Device IP: The IP address of a neighbor router. Port ID: The port ID that a neighbor router is attached to. Link State: The state of the link between a router and its neighbor router. There are two states: Up and Down. Update Time: The time of updating the entry. The format of ADT -------------------------------------------------- Device ID | Device IP | Type | State | Update Time -------------------------------------------------- Device ID: The ID of a neighbor router. Device IP: The IP address of a neighbor router. Type: The type of a neighbor router. State: The state of a neighbor router. There are two states: Up and Down. Update Time: The time of updating the entry. The format of LFT -------------------------------------------- No | Router 1 IP | Router 2 IP | Update Time -------------------------------------------- No: The entry number. Bin Liu, et al. Expires June 22, 2014 [Page 8] Internet-Draft FAR for DCN December 2013 Router 1 IP: The IP address of one router that a failed link connects to. Router 2 IP: THe IP address of another router that a failed link connects to. Update Time: The time of updating the entry. The format of BRT ------------------------------------------------------- Destination | Mask | Next Hop | Interface | Update Time ------------------------------------------------------- Destination: A destination network Mask: The subnet mask of a destination network. Next Hop: The IP address of a next hop for a destination. Interface: The interface related to a next hop. Update Time: The time of updating the entry. The format of NRT ------------------------------------------------------------------- Destination| Mask| Next Hop| Interface| Failed Link No| Timestamp ------------------------------------------------------------------- Destination: A destination network. Mask: The subnet mask of a destination network. Next Hop: The IP address of a next hop that should be avoided for a destination. Interface: The interface related to a next hop that should be avoided. Failed Link No: A group of failed link numbers divided by !o/!+/-, for example 1/2/3. Timestamp: The time of updating the entry. Bin Liu, et al. Expires June 22, 2014 [Page 9] Internet-Draft FAR for DCN December 2013 5.2. Messages Some protocol messages are exchanged between routers in FAR. Hello Message: Be exchanged between neighbor routers to learn adjacency. Device Announcement (DA): Synchronize the knowledge of routers between routers. Link Failure Announcement (LFA): Synchronize link failures between routers. Device and Link Request (DLR): When a router starts, it requests the knowledge of routers and links from its neighbors by a DLR message. A FAR Message is directly encapsulated in an IP packet. The protocol field of IP header indicates an IP packet is an FAR message. The protocol of IP for FAR should be assigned by IANA. The four types of FAR messages have same format of packet header, called FAR header. |<--- 1 --->| <--- 1 --->|<--------- 2 ---------->| +-----------+------------+------------------------+ | Version |Message Type| Message Length | +-----------+------------+------------------------+ | Checksum | AuType | +------------------------+------------------------+ | Authentication | +-------------------------------------------------+ | Authentication | +-------------------------------------------------+ | Timestamp | +-------------------------------------------------+ Figure 2: The format of FAR header Version: FAR version Message Type: the type of FAR message. Packet Length: the packet length of the total FAR message. Checksum: the checksum of an entire FAR message. Bin Liu, et al. Expires June 22, 2014 [Page 10] Internet-Draft FAR for DCN December 2013 AuType:Authentication type. 0: no authentication, 1: Plaintext Authentication, 2: MD5 Authentication. Authentication: Authentication information. 0: undefined, 1: Key, 2: key ID, MD5 data length and packet number. MD5 data is appended to the backend of the packet. AuType and Authentication can refer to the definition of OSPF packet. |<--- 1 --->| <--- 1 --->|<--------- 2 ---------->| +-----------+------------+------------------------+ | Version |Message Type| Message Length | +-----------+------------+------------------------+ | Checksum | AuType | +------------------------+------------------------+ | Authentication | +-------------------------------------------------+ | Authentication | +-------------------------------------------------+ | Timestamp | +-------------------------------------------------+ | Router IP | +------------------------+------------------------+ | HelloInterval | HelloDeadInterval | +------------------------+------------------------+ | Neighbor Router IP | +-------------------------------------------------+ | ... | +-------------------------------------------------+ Figure 3: The format of Hello messages For Hello messages, the Message Type in FAR header is set to 1.Besides FAR header, a Hello message requires the following fields: Router IP: the router IP address. HelloInterval: the interval of sending Hello messages to neighbor routers. RouterDeadInterval: The interval to set a neighbor router dead. If in the interval time, a router doesn!_t receive a Hello message from its neighbor router, the neighbor router is treated as dead. Bin Liu, et al. Expires June 22, 2014 [Page 11] Internet-Draft FAR for DCN December 2013 Neighbor Router IP: the IP address of a neighbor router. All the neighbor router's addresses should be included in a Hello message. |<----1---->| <----1---->|<----------2----------->| +-----------+------------+------------------------+ | Version |Message Type| Message Length | +-----------+------------+------------------------+ | Checksum | AuType | +------------------------+------------------------+ | Authentication | +-------------------------------------------------+ | Authentication | +-------------------------------------------------+ | Timestamp | +------------------------+------------------------+ | Router1 IP | +-------------------------------------------------+ | ... | +-------------------------------------------------+ Figure 4: The format of DA messages For DA messages, the Message Type in FAR header is set to 2. Besides FAR header, a DA message includes IP addresses of all the announced routers. Bin Liu, et al. Expires June 22, 2014 [Page 12] Internet-Draft FAR for DCN December 2013 |<----1---->| <----1---->|<----------2----------->| +-----------+------------+------------------------+ | Version |Message Type| Message Length | +-----------+------------+------------------------+ | Checksum | AuType | +------------------------+------------------------+ | Authentication | +-------------------------------------------------+ | Authentication | +-------------------------------------------------+ | Timestamp | +------------------------+------------------------+ | Left IP | +-------------------------------------------------+ | Right IP | +------------------------+------------------------+ | State | +-------------------------------------------------+ | ... | +-------------------------------------------------+ Figure 5: The format of LFA messages For LFA messages, the Message Type in FAR header is set to 3. Besides FAR header, a LFA message includes all the announced link failures. Left IP: the IP address of the left endpoint router of a link. Right IP: the IP address of the right endpoint router of a link. State: link state. 0: Up, 1: down Bin Liu, et al. Expires June 22, 2014 [Page 13] Internet-Draft FAR for DCN December 2013 |<----1---->| <----1---->|<----------2----------->| +-----------+------------+------------------------+ | Version |Message Type| Message Length | +-----------+------------+------------------------+ | Checksum | AuType | +------------------------+------------------------+ | Authentication | +-------------------------------------------------+ | Authentication | +-------------------------------------------------+ | Timestamp | +-------------------------------------------------+ Figure 6: The format of DLR Messages For DLR messages, the Message Type in FAR header is set to 1.Except for FAR header, DLR has no additional fields. 6. FAR Modules 6.1. Neighbor & Link Detection Module(M1) M1 is responsible for sending and receiving Hello messages, and detecting directly-connected links and neighbor routers. Each Hello message is encapsulated in a UDP packet. M1 sends Hello messages periodically to all the active router ports and receives Hello messages from its neighbor routers. M1 detects neighbor routers and directly-connected links according to received Hello Messages and stores these neighbors and links into a Neighbor Devices Table (NDT). Additionally, M1 also stores the neighbor routers into an All Devices Table (ADT). 6.2. Device Learning Module(M2) M2 is responsible for sending, receiving, and forwarding device announcement (DA) messages, learning all the routers in the whole network, and deducing faulted routers. When a router starts, it sends a DA message announcing itself to its neighbors and a DLR message requesting the knowledge of routers and links from its neighbors. If M2 module of a router receives a DA message, it checks whether the router encapsulated in the message is in an ADT. If the router is not in the ADT, M2 puts this router into the ADT and forwards this DA message to all the active ports except for the incoming one, otherwise, M2 discards this message directly. If M2 module of a router receives a DLR message, it replies a DA message that encapsulates all the learned routers. Bin Liu, et al. Expires June 22, 2014 [Page 14] Internet-Draft FAR for DCN December 2013 6.3. Invisible Neighbor & Link Failure Inferring Module(M3) M3 is responsible for inferring invisible neighbors of the current router by means of the ADT. If the link between a router A and its neighbor B breaks, which results in that M1 module of A cannot detect the existence of B, then B is an invisible neighbor of A. Because a device!_s location has been coded into its IP address, it can be judged whether two routers are adjacent, according to their IP addresses. Based on this idea, M3 infers all the invisible neighbors of the current router and the related link failures. The result stores into a NDT. Moreover, link failures also are added into a link-failure table (LFT). LFT stores all the failed links in the entire network. 6.4. Link Failure Learning Module(M4) M4 is responsible for sending, receiving and forwarding link failure announcement (LFA) and learning all the link failures in the whole network. M4 broadcasts each newly inferred link failure to all the routers in the network. Each link failure is encapsulated in a LFA message and one link failure is broadcasted only once. If a router receives a DLR request from its neighbor, it will reply a LFA message that encapsulates all the learned link failures through M4 module. If M4 receives a LFA message, it checks whether the link failure encapsulated in the message is in a LFT. If the link failure is not in the LFT, M4 puts this link failure into the LFT and forwards this LFA message to all the active ports except for the incoming one, otherwise, M4 discards this message directly. 6.5. BRT Building Module(M5) M5 is responsible for building a BRT for the current router. By leveraging the regularity in topology, M5 can calculate the routing paths for any destination without the knowledge of the topology of whole network, and then build the BRT based on a NDT. Since the IP addresses of network devices are continuous, M5 only creates one route entry for a group of destination addresses that have the same network prefix by means of route aggregation technology. Usually, the size of a BRT is very small. The detail of how to build a BRT is described in section 5. 6.6. NRT Building Module(M6) M6 is responsible for building a NRT for the current router. Because M5 builds a BRT without considering link failures in network, the routing paths calculated by the BRT cannot avoid failed links. To solve this problem, a NRT is used to exclude the routing paths that include some failed links from the paths calculated by a BRT. M6 Bin Liu, et al. Expires June 22, 2014 [Page 15] Internet-Draft FAR for DCN December 2013 calculate the routing paths that include failed links and stored them into the NRT. The detail of how to build a NRT is described in section 5. 6.7. Routing Table Lookup(M7) M7 is responsible for querying routing tables and deciding the next hop for the forwarding packets. Firstly, M7 takes the destination address of a forwarding packet as a criterion to look up route entries in a BRT based on longest prefix match. All of the matched entries are composed of a candidate hops list. Secondly, M7 look up negative route entries in a NRT taking the destination address of the forwarding packet as criteria. In this lookup, Not limited to longest prefix match, any entry that matches the criteria would be selected and composed of an avoiding hops list. Thirdly, the candidate hops minus avoiding hops are composed of an applicable hops list. At last, M7 sends the forwarding packet to any one of the applicable hops. If the applicable list is empty, the forwarding packet will be dropped. 7. Application Example In this section, we take a Fat-tree network as an example to describe how to apply FAR routing. Since M1 to M4 are very simple, we only introduce how the modules M5, M6 & M7 work in a Fat-tree network. A Fat-tree network is composed of 4 layers. The top layer is core layer, and the other layers are aggregation layer, edge layer and server layer. There are k pods, each one containing two layers of k/ 2 switches. Each k-port switch in the edge layer is directly connected to k/2 hosts. The remaining k/2 ports are connected to k/2 of the k-port switches in the aggregation layer. There are (k/2)2 k-port core switches. Each core switch has one port connected to each of k pods. Bin Liu, et al. Expires June 22, 2014 [Page 16] Internet-Draft FAR for DCN December 2013 10.0.1.1 10.0.1.2 10.0.2.1 10.0.2.2 +--+ +--+ +--+ +--+ | | | | | | | | +--+,_ +--+', +--+ ,,+--+ |`,`',`-., / | \ `. .'` - .-'``.` /| | . `', `'., / | ' ' ,-`,' |`. .` ' | | \ `', `-., .` / | `, .` ,' | | `, `'. `'-,_ .'` ,' | ', / | | . `'. `-.,-` / | \ | \ `'., .` `'., ` | `. | `, .'`, ,`'., | ', | . ,-` '., - `'-,_ | `. | \ .` ,'., `|., . | .'` / `-, | `'., `. 10.1.0.1 ,-` . .' 10.3.0.1 10.3.0.2`'., ', +--+ +--+ +--+ +--+ +--+ +--+ +--+ +--+ | | | | | | | | | | | | | | | | +--+ +--+ +--+ +--+ +--+ +--+ +--+ +--+ | \/ | | \/ | | \/ | | \/ | +--+/\+--+ +--+/\+--+ +--+/\+--+ +--+/\+--+ | | | | | | | | | | | | | | | | +--+ +--+ +--+ +--+ +--+ +--+ +--+ +--+ /| 10.1.2.1 /| |\ 10 3.1.3 |\ /| | | / | | \ / | | \ / | | \ / | | | / | | \ / | | \ / | | \ / | | | / | | \ / | | \ / | | \ / | | | ++ ++ ++ ++ ++ ++ ++ ++ ++ ++ ++ ++ ++ ++ ++ ++ ++ ++ ++ ++ ++ ++ ++ ++ ++ ++ ++ ++ ++ ++ ++ ++ 10.1.2.2 10.3.1.3 Figure 7: Fat-tree Aggregation switches are given addresses of the form 10.pod.0.switch, where pod denotes the pod number, and switch denotes the position of that switch in the upper pod (in [1, k/2]). Edge switches are given addresses of the form 10.pod.switch.1, where pod denotes the pod number, and switch denotes the position of that switch in the lower pod (in [1, k/2]). The core switches are given addresses of the form 10.0.j.i, where j and i denote that switch!_s coordinates in the (k/ 2)2 core switch grid (each in[1, (k/2)], starting from top-left). The address of a host follows the pod switch it is connected to; hosts have addresses of the form: 10.pod.switch.ID, where ID is the host's position in that subnet (in [2, k/2+1], starting from left to right). Bin Liu, et al. Expires June 22, 2014 [Page 17] Internet-Draft FAR for DCN December 2013 7.1. BRT Building Procedure By leveraging the topology's regularity, every switch clearly knows how it forwards a packet. When a packet arrives at an edge switch, if the destination of the packet lies in the same subnet with the switch, then the switch directly forwards the packet to the destination server through layer-2 switching; otherwise, the switch forwards the packet to any of aggregation switches in the same pod. When a packet arrives at an aggregation switch, if the destination of the packet lies in the same pod, then the switch forwards the packet to the corresponding edge switch, otherwise, the switch forwards the packet to any of core switches that it is connected to. If a core switch receives a packet, it forwards the packet to the corresponding aggregation switch that lies in the destination pod. The forwarding policy discussed above is easily expressed through a BRT. The BRT of an edge switch, such as 10.1.1.1, is composed of the following entries: Destination/Mask Next hop 10.0.0.0/255.0.0.0 10.1.0.1 10.0.0.0/255.0.0.0 10.1.0.2 The BRT of an aggregation switch, such as 10.1.0.1, is composed of the following entries: Destination/Mask Next hop 10.1.1.0/255 255.255.0 10.1.1.1 10.1.2.0/255.255.255.0 10.1.2.1 10.0.0.0/255.0.0.0 10.0.1.1 10.0.0.0/255.0.0.0 10.0.1.2 The BRT of acore switch, such as 10.0.1.1, is composed of the following entries: Destination/Mask Next hop 10.1.0.0/255 255.0.0 10.1.0.1 10.2.0.0/255.255.0.0 10.2.0.1 10.3.0.0/255.255.0.0 10.3.0.1 10.4.0.0/255.255.0.0 10.4.0.1 7.2. NRT Building Procedure The route entries in a NRT are related with link and node failures. We conclude all kinds of cases into 3 catalogs. Bin Liu, et al. Expires June 22, 2014 [Page 18] Internet-Draft FAR for DCN December 2013 7.2.1. Single Link Failure In Fat-tree, Links can be classified as 3 types by their locations: 1) servers to edge switches; 2) edge to aggregation switches; 3) aggregation to core switches. Link failures between servers to edge switches only affect the communication of the corresponding servers and don't affect the routing tables of any switch, so we only discuss the second and third type of links failures. Edge to Aggregation Switches Suppose that the link between an edge switch, such as 10.1.2.1 (A), and an aggregation switch, such as 10.1.0.1(B),fails. This link failure may affect 3 types of communications. o Sources lie in the same subnet with A, and destinations do not. In this case, the link failure will only affect the routing tables of A. As this link is attached to A directly, A only needs to delete the route entries whose next hop is B in its BRT and add no entries to its NRT when A's M6 module detect the link failure. o Destinations lie in the same subnet with A, and sources lie in another subnet of the same pod. In this case, the link failure will affect the routing tables of all the edge switches in the same pod except for A. When an edge switch, such as 10.1.1.1, learns the link failure, it will add a route entry to its NRT: Destination/Mask Next hop 10.1.2.0/255.255.255.0 10.1.0.1 o Destinations lie in the same subnet with A, sources lie in another pod. In this case, the link failure will affect the routing tables of all the edge switches in the other pods. When an edge switch in one other pod, such as 10.3.1.1, learns the link failure, because all the routings that pass through 10.3.0.1 to A will certainly pass through the link between A and B, 10.3.1.1 need add a route entry to its NRT: Destination/Mask Next hop 10.1.2.0/255.255.255.0 10.3.0.1 Aggregation to Core Switches Suppose that the link between an aggregation switch, such as 10.1.0.1 (A), and a core switch, such as 10.0.1.2(B), fails. This link failure may affect 2 types of communications. Bin Liu, et al. Expires June 22, 2014 [Page 19] Internet-Draft FAR for DCN December 2013 o Sources lie in the same pod (pod 1) with A, and destinations lie in the other pods. In this case, the link failure will only affect the routing tables of A. As this link is attached to A directly, A only need to delete the route entries whose next hop is B in its BRT and add no entries to its NRT when A!_s M6 module detect the link failure. o Destinations lie in the same pod (pod 1) with A, and sources lie in another pod. In this case, the link failure will affect the routing tables of all the aggregation switches in other pods except for pod 1. When an aggregation switch in one other pod, such as 10.3.0.1, learns the link failure, because all the routings that pass through 10.0.1.2 to the pod 1 where A lies will certainly pass through the link between A and B, 10.3.0.1 need add a route entry to its NRT: Destination/Mask Next hop 10.1.0.0/255.255.0.0 10.0.1.2 7.2.2. A Group of Link Failures If all the uplinks of an aggregation switch fail, then this switch cannot forward packets, which will affect the routing of every edge switches. Suppose that all the uplinks of the node A (10.1.0.1) fail, it will affect two types of communications. o Sources lie in the same pod (pod 1) with A, and destinations lie in the other pods. In this case, the link failures will affect the routing of the edge switches in the Pod of A. To avoid the node A, each edge switch should remove the route entry !o10.0.0.0/ 255.0.0.0GBP[not]10.1.0.1!+/- in which the next hop is the node A. o Destinations lie in the same pod (pod 1) with A, and sources lie in other pods. In this case, the link failures will affect the routing of edge switches in other pods. For example, if the edge switch 10.3.1.1 communicates with some node in the pod of A, it should avoid the node 10.3.0.1, because any communication through 10.3.0.1 to the pod of A will pass through the node A. So a route entry should be added to 10.3.1.1: Destination/Mask Next hop 10.1.0.0/255.255.0.0 10.3.0.1 7.2.3. Node Failures Bin Liu, et al. Expires June 22, 2014 [Page 20] Internet-Draft FAR for DCN December 2013 At last, we discuss the effect of node failures to a NRT. There are 3 types of node failures: the failure of edge, aggregation and core switches. o An edge switch fails. The failure doesn't affect the routing table of any switch. o A core switch fails. Only when all the core switches connected to the same aggregation switch fail, they will affect the routing of other switches. This case is equal to the case that all the uplinks of an aggregation switch fail, so the process of link failures can cover it. o An aggregation switch fails. This case is similar to the case that all the uplinks of an aggregation switch fail. It affects the routing of edge switches in other pods, but doesn't affect the routing of edge switches in pod of the failed switch. The process of this failure is same to the second case in section 6.2.2. 7.3. Routing Procedure FAR decides a routing by looking up its BRT and NRT. We illuminate the routing procedure by an example. In this example, we suppose that the link between 10.3.1.1 and 10.3.0.2 and the link between 10.1.2.1 and 10.1.0.2 have failed. Then we look into the routing procedure of a communication from 10.3.1.3 (source) to 10.1.2.2 (destination). Step 1: The source 10.3.1.3 sends packets to its default router 10.3.1.1 Step 2: The routing of 10.3.1.1. 1) Calculate candidate hops 10.3.1.1 looks up its BRT and gets the following matched entriesGBPo Destination/Mask Next hop 10.0.0.0/255.0.0.0 10.3.0.1 So the candidate hops = {10.3.0.1} 2) Calculate avoiding hops Its NRT is empty, so the set of avoiding hop is empty too. 3) Calculate applicable hops Bin Liu, et al. Expires June 22, 2014 [Page 21] Internet-Draft FAR for DCN December 2013 The applicable hops are candidate hops minus avoiding hops, so: The applicable hops = {10.3.0.1} 4) Forward packets to 10.3.0.1 Step 3: The routing of 10.3.0.1 1) Calculate candidate hops. 10.3. 0.1 looks up its BRT and gets the following matched entriesGBPo Destination/Mask Next hop 10.1.0.0/255.255.0.0 10.0.1.1 10.1.0.0/255.255.0.0 10.0.1.2 So the candidate hops = {10.0.1.1, 10.0.1.2} 2) Calculate avoiding hops Destination/Mask Next hop 10.1.0.0/255.255.0.0 10.0.1.2 So the avoiding hops = {10.0.1.2} 3) Calculate applicable hops The applicable hops are candidate hops minus avoiding hops, so: The applicable hops = {10.0.1.1} 4) Forward packets to 10.0.1.1 Step 4: 10.0.1.1 forwards packets to 10.1.0.1 by looking up its routing tables. Step 5: 10.1.0.1 forwards packets to 10.1.2.1 by looking up its routing tables. Step 6:10.1.2.1 forwards packets to the destination 10.1.2.2 by layer-2 switching. 8. Conclusion Bin Liu, et al. Expires June 22, 2014 [Page 22] Internet-Draft FAR for DCN December 2013 This draft introduces FAR protocol, a generic routing method and protocol, for data centers that have a regular topology. It uses two routing tables, a BRT and a NRT, to store the normal routing paths and avoiding routing paths, respectively, which makes FAR very simple and efficient. The sizes of two tables are very small. Usually, a BRT has only several tens of entries and a NRT has only several or about a dozen entries. 9. Reference [FAT-TREE] M. Al-Fares, A. Loukissas, and A. Vahdat."A Scalable,Commodity, Data Center Network Architecture",In ACM SIGCOMM 2008. 10. Acknowledgments This document is supported by ZTE Enterprise-University-Research Joint Project. 11. Security Considerations Authors' Addresses Bin Liu ZTE Inc. ZTE Plaza, No.19 East Huayuan Road,Haidian District Beijing 100191 China Email: liu.bin21@zte.com.cn Yantao Sun Beijing Jiaotong University No.3 Shang Yuan Cun, Hai Dian District Beijing 100044 China Email: ytsun@bjtu.edu.cn Jing Cheng Beijing Jiaotong University No.3 Shang Yuan Cun, Hai Dian District Beijing 100044 China Email: yourney.j@gmail.com Bin Liu, et al. Expires June 22, 2014 [Page 23] Internet-Draft FAR for DCN December 2013 Yichen Zhang Beijing Jiaotong University No.3 Shang Yuan Cun, Hai Dian District Beijing 100044 China Email: snowfall_dan@sina.com Bin Liu, et al. Expires June 22, 2014 [Page 24]