Design and Implementation of an Anycast Efficient QoS Routing on OSPFv3

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1 Design and Implementation of an Anycast Efficient QoS Routing on OSPFv3 Han Zhi-nan Yan Wei Zhang Li Wang Yue Computer Network Laboratory Department of Computer Science & Technology, Peking University Beijing, China Computer Network Laboratory Department of Computer Science & Technology, Peking University Beijing, China Computer Network Laboratory Department of Computer Science & Technology, Peking University Beijing, China Computer Network Laboratory Department of Computer Science & Technology, Peking University Beijing, China Tel: Tel: u.cn Tel: cn Tel: u.cn ABSTRACT Anycast is a service mainly provided in IPv6. According to the definition of anycast, there is a group of hosts, which are assigned a same anycast address and the packets sent to this address will be directed to the nearest host by anycast-supported router. There are some problems to route anycast datagram using normal unicast routing protocol, such as OSPFv3. Therefore, OSPFv3 is extended to support anycast address and anycast QoS routing based on our anycast QoS routing algorithm proposed. Some new features are added to the implementation of OSPFv3, such as support reversed routing calculation, bandwidth levels routing and so on. New OSPFv3 is experimented on test bed; the result proves the new routing system is feasible and efficient. Categories and Subject Descriptors C.2.2 [Computer-Communication networks]: Network Protocols - Routing protocols. General Terms Algorithms, Design, Performance. Keywords Anycast, Routing Algorithm, OSPFv3, QoS. 1. INTRODUCTION Anycast is a service, which will probably be popular in IPv6 networks, allows a sender to access the nearest of a group of hosts that share a same anycast address. It is a good mechanism to improve the performance of services. Anycast has large numbers of prospective applications. For instance, a group of FTP servers which are assigned the same anycast address can automatically make clients download files from the nearest replica so that it will bring shorter response time. When the clients have some quality requirement of service, such as bandwidth requirement of online movie service, anycast and the QoS routing based on

2 it will do the best because anycast can make sure the highest response speed while the QoS routing chooses a better server among all the copies and provides a steady and fast path from this server to the client. So in order to make the further improvement of the performance, research on the anycast QoS efficient routing is significant. Recently, a lot of works have aimed at some valuable improvement on the QoS routing. But less works focus on a concrete proposal, based on a certain existing routing protocol such as Open Shortest Path First (OSPF). For example, ref[9] gives some pre-computation mechanisms of QoS routing and OSPF extensions while ref[10] implements the QoS routing extensions to OSPF. And even lesser works discuss Anycast based on QoS routing, ref[11] discusses the motivation and gives an architecture of QoS routing for Anycast for DiffServ networks. Till now, there have hardly been any works designing Anycast QoS routing system based on OSPF protocol and able to give an implementation. To fill this gap, this paper deals with an efficient Anycast QoS routing, this is not a general discussing but a design and implementation on OSPF. anyone of them has nothing different. There are two kinds of servers seem most possibly supplied by anycast servers. One is great quantities of data being transported from server to clients, such as kinds of download services and online video or audio services; we can call it Data-Supplied-Type. The other is Servings-Supplied-Type which supply services such as DNS and website mirror, with a small quantity of data being sent between clients and server. To keep the consistency of all replicas in an anycast group, the services like upload should not likely to be provided by anycast servers. From the analyzing above, we can get the following conclusions: a) It can be found that more data from servers to clients than from clients to servers totally. So the attention should be focused on the quality and speed from server to client when designing the path selection algorithm. b) Transporting of large quantities of data is a big part of services, therefore the Bandwidth should be considered in the QoS routing. c) Because there are more than one replica we can choose, we should choose the server whose load is light enough. So another metric ---- Server Load is introduced into the QoS routing. The paper is organized as follows. The next section shows the background and aim of the research. Section 3 discusses the design of Anycast QoS routing algorithm. The details of implementation on OSPFv3 are described in Section 4. In Section 5, we do experiment and analyze the result to show the correctness and availability of our design. Finally, Section 6 presents our conclusion. 2. BACKGROUND 2.1 Anycast QoS Routing As discussed above, our QoS routing algorithm is for Anycast. So this algorithm should adequately consider the characteristic of Anycast. The hosts with anycast address in an anycast group are often servers, they present a same service and therefore connecting to 2.2 The OSPFv3 Protocol Open Shortest Path First (OSPF) is a link state routing protocol. According to this protocol, each router maintains the full topology of the network in a link state database. The OSPF standard specifies that routers implementing the protocol run a shortest path Dijkstra computation on their local link state database, and determine the shortest paths to all other nodes in the network. The database is constructed and updated by means of link state advertisements that are generated by each router and propagated to all other routers using reliable flooding. The flooding procedure utilizes a variety of packet types: Link State Update (LSU) packets contain information about changes in the topology, and are used to carry multiple Link State Advertisements (LSAs). Link State Acknowledgment packets are used

3 to acknowledge receipt of link state advertisements. Finally, Database Description and Link State Request packets are used to synchronize the link state databases of neighboring routers. There are also several types of link state advertisements, with router and network link advertisements being the most relevant ones for our purpose. Router LSAs contain information about a router and all its interfaces, while network LSAs describe the set of routers attached to a given network. Link state advertisements are either generated periodically or are triggered by topology changes such as link failures or recoveries. These advertisements contain cost metrics that are used to compute the shortest path. supports QoS routing based on the OSPFv3 protocol, firstly, we need to solve the following problems: 1. The recent OSPFv3 should be adapted to the Anycast address. 2. Add the QoS metric Bandwidth and Server Load into the OSPFv3 and deal with them. 3. The path calculation should choose the best way from server to the client. 4. Solve the address resolution problem 3. ALGORITHM DESIGN OSPF allows for a two level hierarchy of areas within the Autonomous System ---- intra-area and inter-area. Routing takes place on this two levels, depending on whether the source and destination of a packet reside in the same area (intra-area routing is used) or different areas (inter-area routing is used). This protects intra-area routing from the injection of bad routing information. OSPFv3 ref[6] is the third version of the OSPF protocol which is for IPv6. The basal mechanisms of OSPFv3 are the same as OSPF, such as flooding, area supporting, shortest path calculation algorithm and so on. However, some changes have been necessary. Besides handling the increased address size of IPv6 and changes in protocol semantics between IPv4 and IPv6, it takes the following changes: 1. Addressing semantics have been removed from all packets and LSAs except in Link-LSAs. 2. Different LSAs have different flooding scope. In particular, Link-LSAs are flooded only on the local link while Router-LSAs, Network-LSAs and Inter-Area-Prefix-LSAs are flooded throughout a single OSPF area. 3. Explicit Support for multiple instances per link. 4. Support stub area. 2.3 Requirements and aims In order to design an Anycast routing algorithm which 3.1 Anycast Address Supporting Members of an IPv6 anycast group may belong to different subnets of an address prefix P, while OSPFv3 can only support the routing information of prefix P. So it cannot process group ID and locate the subnets which the members in. We have shown how to modify OSPFv3 to support anycast address in ref[3]. In that paper, the method has been implemented and proved to be feasible and correct, so in this paper, we still use that method and implementation. 3.2 Bandwidth Metric Supporting We classify the preservable bandwidth of network, which still can be reserved, into several levels. If we divide 300M bandwidth equally into 3 levels, then the first level means the bandwidth above 0M while the third level means the bandwidth above 200M. Our algorithm creates some topological graphs corresponding to the levels, there are only nodes according with the bandwidth requirement of the level in each topological graph. So when clients ask for transporting of any level, the algorithm can return the next hop in the routing path calculated based on the topology of that level. For example, if there are five levels path in the network, when a client asks for level two s transporting from the destination, the next hop to that destination in the path of level two s topological graph will be returned.

4 3.3 Server Load Metric Supporting Taking the load of sever into consideration, we need a small monitor process on each Anycast Server sending information of the Server Load to the routing program on the routers by group management program ref[12]. The information contains the load percentage from zero to one hundred of the server. For instance, a FTP sever can set an upper limit of the flow, then the monitor process sends the percentage of the current flow in total allowable flow to the routing program. After get the Sever Load of a group of servers with the same anycast address, the program takes the following judgments: if there is at least one server s load is lower than 0.5, let the servers whose load is lower than 0.5 take part in the route calculating; otherwise, if all servers load are higher than 0.5, then choose the lowest server to take part in the route calculating. 4. IMPLEMENTATION ON OSPFv3 We use the software named zebra which is a ready-to-wear OSPFv3 implementation. Its source codes are opened and we can do some modifications based on it. Further more, we base on the modified zebra which has been described in ref[3]. 4.1 New LSAs In order to advertise the Bandwidth information of routers and the Server Load information of servers, we add two new types of LSAs called Reservable-Bandwidth-Lsa and Server-Load-Lsa with formats shown in Figure 1.a and Figure1.b: Figure 1.a: Format of Reservable-Bandwidth-Lsa

5 Figure 1.b: Format of Server-Load-Lsa They are flooded as other LSAs and also stored in the link state database. 4.2 Bandwidth Supporting We implement the support to bandwidth based on the shortest path tree building process of OSPFv3. As described in the second section, a router implementing OSPFv3 runs a shortest path Dijkstra computation on their local link state database to determine the shortest paths to all other nodes in the network. In order to record the shortest paths to all other node in the network, the router builds a shortest paths tree. The tree's nodes are routers, transit networks and stub networks. This shortest path tree is built by following steps: 1) Create a candidate list to store the vertex which will be appended into the shortest path tree. Initialize the shortest path tree, with the router itself as the root of the shortest paths tree and add it to the candidate list. 2) Call the vertex just added to the tree vertex V. Examine the LSA associated with vertex V and get another vertex called vertex W. After confirm W s existence, no repetition and no stub network, judge V is a router (the LSA s type is Router-Lsa) or a transit network (the LSA s type is Network-Lsa). If router, add the metric of the vertex V s interface which connect to W to the cost of the path from root to vertex V as the cost of the path from root to vertex W; else if network, the cost from root to vertex W is equal to the cost to vertex V. Add vertex W to the candidate list and repeat step 2 until all LSA associated with vertex V have been checked. 3) Add the node which is nearest to the root in the candidate list into the shortest path tree and delete it from the candidate list. Do step 2 until the candidate list is empty 4) Add the stub networks into the tree as leaves and the shortest path tree building is done. Based on these steps, we do the following modifications: i. Before calculating the shortest path tree, we add sub-trees into the shortest path tree and each sub-tree represents a level of bandwidth,

6 assuming the number of levels is N. ii. Create N copies of the router itself as roots of all sub-trees and N candidate lists providing candidates for the sub-tree of each level. Then add roots to the candidate lists. iii. A cycle is added to deal with candidates from each candidate list. In the cycle, we do the step 2), 3) described above with the modification that: when creating vertex W, if the type of its Lsa is Router-Lsa, we check the Reservable-Bandwidth-Lsa whose advertising router is W. (This because we need to focus on the reverse routing features include bandwidth.) According to the Bandwidth Level of the Reservable-Bandwidth-Lsa, if the bandwidth level of vertex W is lower than the current candidate list which vertex V is from, it will be discarded, otherwise, it will be added to the current candidate list. iv. An anycast address can be on more than one links, so it can appear in several Intra-Area-Prefix-Lsa. Router connects these Intra-Area-Prefix-Lsas to the corresponding vertex of the shortest path tree ref[3] and adds the metric of the Intra-Area-Prefix-Lsa to the cost from root to the router as the cost from root to the anycast server. Then to different anycast servers have different costs, even they have the same anycast address. After this action, the path on the shortest path tree to an anycast address may be more than one and not the shortest. We will calculate the shortest one among paths to an anycast address when we insert the route information into the route table. By the modification shown above, the shortest path tree with N sub-trees has been done and it can do routing with bandwidth requirements. 1) Get the Intra-Area-Prefix-Lsa of each router, check if it represents an anycast server. If does, do 2); otherwise, do 1). 2) Find corresponding Server-Load-Lsa of the server in the link state database. If the Server Load in the Server-Load-Lsa is not higher than 0.5, do 7), otherwise, do 3). 3) Check the SL-list to find out whether there is already a node whose address of anycast server is same as the current server address advertised by the router. If there is, do 4); otherwise, do 6). 4) Compare the Server Load of the node in SL-list with the Server Load of the current Server-Load-Lsa, if larger, do 5); otherwise, do 1). 5) Remove the connection between the advertising router of the node in SL-list and Intra-Area-Prefix-Lsa in the sub-tree of shortest path tree and delete the Replace the Server Load and advertising router of the node in SL-list with the Server Load and advertising router of current Server-Load-Lsa. Then do 1). 6) Add a new node with the anycast address of server, Server Load and the advertising into the SL-list, then examine the next node of SLL-list and do 1). 7) Check the SL-list to find out whether there is already a node whose address of anycast server is same as the current server address advertised by the router. If there is, do 8); otherwise, do 1). 8) If the Server Load of the node in SL-list which has same address as the current server is higher than 0.5, do 5); otherwise, do 1). When the two level s cycles described above are over, all servers that have too heavy load have been discard from the shortest path tree. 4.3 Server Load Processing To process Server Load, a new structure SL-list is created. SL-list is a linked list that stores the Server Load and advertising router of an anycast server. After the shortest path tree is built, we need an extra check to each sub-tree. In each sub-tree: 4.4 Finishing the Implementation After processing Bandwidth and Server Load, we need to do some more work to make our implementation integrated and available. 1) Change the route table in OSPFv3. Insert N sub-tables into the route table and each table

7 shows routing information of each bandwidth. 2) Check Intra-Area-Prefix-Lsas connected with each sub-tree again. If there are more than one Intra-Area-Prefix-Lsas represent a same anycast address, compare the cost of them and find the shortest path to this anycast address. 3) According to the result of step 2), insert the routing information to all anycast addresses into the route table. 4) According to the shortest path tree we have built, insert other routing information into the route table. 5) Give a function as an interface to the source reserve program such RSVP program. The parameters of this function are the destination address and the bandwidth level while the function will return the next hop in the shortest path to the destination in the sub-table of the appointed level or information of failure. After doing all above, our implementation is completed and we will prove it is feasible and efficient by experimenting in the next section. Figure 2 show the topology of our test bed. And there are three anycast servers with a same anycast address fec0:c002:1123/32 and same metric in Intra-Area-Prefix-Lsa which represent the cost from the anycast server to the router which advertise the network. But A1 is in Network1 with Server Load 0.4, A2 is in Network3 with Server Load 0.6 and A3 is in Network5 with Server Load 0.4. The address of each network is shown below: N1: fec0:c002:03::/40 N2: fec0:c002:04::/40 N3: fec0:c002:05::/40 N4: fec0:c002:06::/40 N5: fec0:c002:07::/40 N6: fec0:c002:08::/40 The number near each router is the cost of link out of the router s interface and we set the bandwidth with two levels and the number after the letter L represents the bandwidth level of link out of the router s interface. The routers run our implementation Anycast QoS Routing on OSPFv3. We can see the shortest path tree through the show function. Figure 3 is the shortest path tree see from R3: 5. RESULT ANALYZING We design a simple IPv6 anycast QoS test bed to prove our design and implementation of the Anycast QoS Routing is feasible and efficient. Figure 3: The Shortest Path Tree of R3 Figure 2: Anycast QoS Routing Test Bed (number near the edge means the cost of the path and no number means cost is zero)

8 From Figure 3, we can find that in the Level 2 s sub-tree, the next hop from root (R3) to R2 is R4 different from R1 in Level 1 s sub-tree. That s because the bandwidth from R2 to N2 is too small to satisfying the requirement of Level 2. Further more, there is no longer path to R5 and N5 in Level 2 s sub-tree. The result show that the shortest paths are calculated according to the reverse cost and two sub-trees are built based on the bandwidth levels. 6. CONCLUSION OSPFv3 is a routing protocol without considering Anycast and QoS Routing. Our design now is proved can be implemented on the OSPFv3 and work well. The modified routing program gives the efficient path to the anycast servers. We also can see the OSPF route table through the show function. Table 1 is the route table seen from R3: Bandwidth Destination Next Cost level hop 1 fec0:c002:1123/32 R5 3 1 fec0:c002:03::/40 R1 8 1 fec0:c002:04::/40 R1 8 1 fec0:c002:05::/40 R4 4 1 fec0:c002:06::/40 R4 4 1 fec0:c002:07::/40 R5 2 1 fec0:c002:08::/40 R fec0:c002:1123/32 R1 8 2 fec0:c002:03::/40 R1 8 2 fec0:c002:04::/40 R1 8 2 fec0:c002:05::/40 R4 4 2 fec0:c002:06::/40 R4 4 2 fec0:c002:08::/40 R4 10 Table 1: The Route Table of R3 According to the Table 1, in Bandwidth Level 1, the next hop to the anycast server which anycast address is fec0:c002:1123/32 is R5. The reason is that A1 and A3 s Server Loads are both lower than 0.5, but the cost of the path to A3 through R5 is shorter than to A1 through R1. While in Bandwidth Level 2, cause there no path to R5 and the Server Load of A1 is better than that of A2, the next hop to the anycast server fec0:c002:1123/32 is R1. This table shows that anycast server with lower load and nearer distance will be chosen by the program. 7. REFERENCE [1] Zhang Li, Yan Wei, Li Xiao-ming. ANYCAST ANOTHER COMMUNICATION MODEL FOR IP. Journal of Computer Research and Development, June 2003, Vol.40, No.6: 784~790 [2] ZHANG Li, WANG Yue, YAN Wei. Reverse Anycast QoS Routing Protocol, 16th APAN Meetings/Advanced Network Conference, August, 2003:155~160. [3] Wang Yue,Zhang Li,Han Zhi-nan,Yan Wei. IPv6 Anycast Routing Support by Extending OSPFv3. Computer Engineer. [4] C. Partridge, T. Mendez, W. Milliken. Host anycasting service. RFC1546, IETF, 1993 [5] J. Moy. OSPF Version 2. RFC2328, IETF, 1998 [6] R. Coltun, D. Ferguson, J. Moy. OSPF for IPv6. RFC2740, IETF, 1999 [7] Kunihiro Ishiguro, Yoshinari Yoshikawa, etc, GNU Zebra: Free routing software distributed under GNU General Public License. [8] Dina Katabi, John Wroclawski. A Framework for Scalable Global IP-Anycast(GIA). ACM SIGCOMM Computer Communication Review, volume 31, Issue 2 supplement, April, 2001:186~219

9 [9] Roch A. Guerin, Ariel Orda, Douglas Williams. QoS Routing Mechanisms and OSPF Extensions. Global Telecommunications Conference, IEEE, Volume: 3, 3-8 Nov. 1997: Management. 16th APAN Meetings/Advanced Network Conference, August, 2003:49~55. [10] G. Apostolopoulos, R. Guerin, S. Kamat. RESEARCH FUND Implementation and Performance Measurements of QoS Routing Extensions to OSPF. INFOCOM '99. Eighteenth Annual Joint Conference of the IEEE Computer and Communications Societies. IEEE, Volume: 2, March 1999: [11] Fang Hao, Ellen W. Zegura, Mostafa H. Ammar. QoS Routing for Anycast Communications: Motivation and an Architecture for DiffServ Network. IEEE Cmmunications Magazine, June 2002: 48~56 The research gets the support of National Natural Science Fund of China task and National 863 task 2001AA2130. Author Han Zhi-nan s research gets the support of President s Fund of Peking University. [12] WANG Yue, ZHANG Li, YAN Wei. Research on IP Anycast Secure Group