Tài liệu Building monitoring tool for core network using bgp protocol

HO CHI MINH CITY UNIVERSITY OF TECHNOLOGY VIET NAM NATIONAL UNIVERSITY, HO CHI MINH CITY HO CHI MINH CITY UNIVERSITY OF TECHNOLOGY FACULTY OF COMPUTER SCIENCE & ENGINEERING THESIS BUILIDING MONITORING TOOL FOR CORE NETWORK USING BGP PROTOCOL MAJOR: COMPUTER ENGINEERING INSTRUCTOR: PhD. NGUYEN LE DUY LAI REVIEWER: PhD. NGUYEN DUC THAI STUDENT : NGUYEN DINH TUAN ± 1552411 VO NAM HAI - 1652178 HO CHI MINH City, December 2021 Monitoring tool for BGP Protocol Page 0 HO CHI MINH CITY UNIVERSITY OF TECHNOLOGY ĈҤI HӐC QUӔC GIA TP.HCM CӜNG HÒA Xà HӜI CHӪ 1*+Ƭ$9,ӊT NAM Ĉӝc lұp - Tӵ do - Hҥnh phúc ---------75ѬӠ1*ĈҤI HӐC BÁCH KHOA KHOA: Khoa hӑc và Kӻ thuұt Máy tính BӜ MÔN: HӋ thӕng và Mҥng NHIӊM VӨ LUҰN ÁN TӔT NGHIӊP Chú ý: Sinh viên ph̫i dán tͥ này vào trang nh̭t cͯa b̫n thuy͇t trình HӐ VÀ TÊN: Võ Nam Hҧi ______________________ MSSV: 1652178 ______ NGÀNH: Khoa hӑc Máy tính __________ LӞP: _______________ ĈҫXÿӅ luұn án: (TiӃng ViӋt): Xây dӵng công cө giám sát mҥng lõi sӱ dөng giao thӭc BGP (English): Building monitoring tool for the core network using BGP protocol. 2. NhiӋm vө (yêu cҫu vӅ nӝi dung và sӕ liӋXEDQÿҫu): Objectives: The BGP protocol has become a fundamental part of the operation and performance of the Internet. As the de facto Internet interǦdomain routing protocol, the BGP protocol has a number of vulnerabilities and weaknesses. Monitoring BGP is an effective way to improve the security of interǦdomain routing In addition, SoftwareDefined Networking (SDN) appears with the idea to decouple the vertically coupled architecture and reconstruct the Internet as a modular structure and Border Gateway Protocol (BGP) participates in transitioning the existing networks to SDN. Therefore, it is obvious that we should undertake the BGP monitoring process when monitoring applications or those services that are offered being Internet the basis of its communication. Tasks: 9 Get the background by studying the BGP protocol 9 List main challenges as far as BGP monitoring is concerned 9 Raise problems that can be evaluated according to the fundamental processes of the BGP protocol. 9 Define the monitoring metrics and functionality to monitor BGP routing information on the routing device Monitoring tool for BGP Protocol Page 1 HO CHI MINH CITY UNIVERSITY OF TECHNOLOGY 9 Propose a monitoring platform and build a monitoring tool for the BGP network 9 Evaluate the real need for a possible monitoring scheme. Required results: 9 Report and demo of monitoring tool operations 3. Ngày giao nhiӋm vө luұn án: ___/___/___. 4. Ngày hoàn thành nhiӋm vө: ___/___/___. 5. Hӑ tên giҧng viên hѭӟng dүn: PhҫQKѭӟng dүn: 1) T.S NguyӉn Lê Duy Lai 100% Nӝi dung và yêu cҫX/971ÿmÿѭӧc thông qua Bӝ môn. 1Jj\WKiQJQăP CHӪ NHIӊM BӜ MÔN GIҦ1*9,Ç1+ѬӞNG DҮN CHÍNH (Ký và ghi rõ h͕ tên) (Ký và ghi rõ h͕ tên) NguyӉn Lê Duy Lai PḪN DÀNH CHO KHOA, B͠ MÔN: 1Jѭӡi duyӋt (chҩPVѫEӝ):________________________ ĈѫQYӏ: _______________________________________ Ngày bҧo vӋ: __________________________________ ĈLӇm tәng kӃt: _________________________________ 1ѫLOѭXWUӳ luұn án: _____________________________ Monitoring tool for BGP Protocol Page 2 HO CHI MINH CITY UNIVERSITY OF TECHNOLOGY ĈҤI HӐC QUӔC GIA TP.HCM CӜNG HÒA Xà HӜI CHӪ 1*+Ƭ$9,ӊT NAM Ĉӝc lұp - Tӵ do - Hҥnh phúc ---------75ѬӠ1*ĈҤI HӐC BÁCH KHOA KHOA: Khoa hӑc và Kӻ thuұt Máy tính BӜ MÔN: HӋ thӕng và Mҥng NHIӊM VӨ LUҰN ÁN TӔT NGHIӊP Chú ý: Sinh viên ph̫i dán tͥ này vào trang nh̭t cͯa b̫n thuy͇t trình HӐ VÀ TÊN: NguyӉQĈuQK7Xҩn ________________ MSSV: 1552411 ______ NGÀNH: Khoa hӑc Máy tính __________ LӞP: _______________ ĈҫXÿӅ luұn án: (TiӃng ViӋt): Xây dӵng công cө giám sát mҥng lõi sӱ dөng giao thӭc BGP (English): Building monitoring tool for the core network using BGP protocol. 2. NhiӋm vө (yêu cҫu vӅ nӝi dung và sӕ liӋXEDQÿҫu): Objectives: The BGP protocol has become a fundamental part of the operation and performance of the Internet. As the de facto Internet interǦdomain routing protocol, the BGP protocol has a number of vulnerabilities and weaknesses. Monitoring BGP is an effective way to improve the security of interǦdomain routing In addition, SoftwareDefined Networking (SDN) appears with the idea to decouple the vertically coupled architecture and reconstruct the Internet as a modular structure and Border Gateway Protocol (BGP) participates in transitioning the existing networks to SDN. Therefore, it is obvious that we should undertake the BGP monitoring process when monitoring applications or those services that are offered being Internet the basis of its communication. Tasks: 9 Get the background by studying the BGP protocol 9 List main challenges as far as BGP monitoring is concerned 9 Raise problems that can be evaluated according to the fundamental processes of the BGP protocol. 9 Define the monitoring metrics and functionality to monitor BGP routing information on the routing device Monitoring tool for BGP Protocol Page 3 HO CHI MINH CITY UNIVERSITY OF TECHNOLOGY 9 Propose a monitoring platform and build a monitoring tool for the BGP network 9 Evaluate the real need for a possible monitoring scheme. Required results: 9 Report and demo of monitoring tool operations 3. Ngày giao nhiӋm vө luұn án: ___/___/___. 4. Ngày hoàn thành nhiӋm vө: ___/___/___. 5. Hӑ tên giҧng viên hѭӟng dүn: PhҫQKѭӟng dүn: 2) T.S NguyӉn Lê Duy Lai 100% Nӝi dung và yêu cҫX/971ÿmÿѭӧc thông qua Bӝ môn. 1Jj\WKiQJQăP CHӪ NHIӊM BӜ MÔN GIҦ1*9,Ç1+ѬӞNG DҮN CHÍNH (Ký và ghi rõ h͕ tên) (Ký và ghi rõ h͕ tên) NguyӉn Lê Duy Lai PḪN DÀNH CHO KHOA, B͠ MÔN: 1Jѭӡi duyӋt (chҩPVѫEӝ):________________________ ĈѫQYӏ: _______________________________________ Ngày bҧo vӋ: __________________________________ ĈLӇm tәng kӃt: _________________________________ 1ѫLOѭXWUӳ luұn án: _____________________________ Monitoring tool for BGP Protocol Page 4 HO CHI MINH CITY UNIVERSITY OF TECHNOLOGY 75ѬӠ1*ĈҤI HӐC BÁCH KHOA CӜNG HÒA Xà HӜI CHӪ 1*+Ƭ$9,ӊT NAM Ĉӝc lұp - Tӵ do - Hҥnh phúc KHOA KH & KT MÁY TÍNH ---------------------------Ngày 24 tháng 12 QăP 2021. PHIӂU CHҨM BҦO Vӊ LVTN 'jQKFKRQJ˱ͥLK˱ͣng d̳n/ph̫n bi͏n) 1. Hӑ và tên SV: x 9}1DP+ҧi - MSSV: 1652178 1JX\ӉQĈuQK7Xҩn - MSSV: 1552411 Ngành (chuyên ngành): ĈӅ tài: BUILIDING MONITORING TOOL FOR CORE NETWORK USING BGP PROTOCOL 3. Hӑ WrQQJѭӡLKѭӟng dүn/phҧn biӋn: NguyӉn Lê Duy Lai 4. Tәng quát vӅ bҧn thuyӃt minh: Sӕ trang: 64 Sӕ FKѭѫQJ 5 Sӕ bҧng sӕ liӋu: Sӕ hình vӁ: 53 Sӕ tài liӋu tham khҧo: 13 Phҫn mӅm tính toán: HiӋn vұt (sҧn phҭm) 5. Tәng quát vӅ các bҧn vӁ: - Sӕ bҧn vӁ: Bҧn A1: - Sӕ bҧn vӁ vӁ tay Bҧn A2: Khә khác: Sӕ bҧn vӁ trên máy tính: 6. NhӳQJѭXÿLӇm chính cӫa LVTN: In this dissertation, the thesis has been studying the BGP as well as the challenges of BGP monitoring. Some monitoring metrics and functionality to monitor BGP routing information on the routing devices are raised in such as peer_as, peer_ip, as_path, asn. The thesis presented how to design and build a monitoring tool for the BGP network following the Cooperative Information Sharing Model (CoISM). The implementation of the BGP Monitor tool helps in the identification of BGP IP prefix disputes and their categorization as BGP hijacking incidents. BGP Monitor then analyses BGP communications that have been Monitoring tool for BGP Protocol Page 5 HO CHI MINH CITY UNIVERSITY OF TECHNOLOGY archived in MRT files. This tool is evaluated with the number of prefix counts and elapsed time for processing file dumps. 7. Nhӳng thiӃu sót chính cӫa LVTN: However, the presented topic is still limited including the inability to support more issues such as BGP Route Misconfigurations, Route Flapping, Infrastructure Failures, DDoS Attacks. The tool built based on CoISM missed the real-time processing. The thesis needs a more thorough survey on some most common BGP Monitoring tools that deliver frequent updates, as often as each minute, giving users the most up-to-date information quickly and minimizing the delay needed to identify and respond to issues. ĈӅ nghӏĈѭӧc bҧo vӋ † † Bә VXQJWKrPÿӇ bҧo vӋ † .K{QJÿѭӧc bҧo vӋ 9. 3 câu hӓi SV phҧi trҧ lӡLWUѭӟc HӝLÿӗng: a. Why do BGP problems occur? Give some examples on BGP issues if someone starts to broadcast a duplicate address or simply one that overlaps with an existing subnet? b. In which ways a route hijacking can occur deliberately or by accident? c. How a serious hijack case can affect the entire Internet? (consequences of route hijacking) ĈiQKJLiFKXQJEҵng chӳ: giӓi, khá, TB): ĈLӇm : 7.5 /10 Ký tên (ghi rõ hӑ tên) NguyӉn Lê Duy Lai Monitoring tool for BGP Protocol Page 6 HO CHI MINH CITY UNIVERSITY OF TECHNOLOGY 75ѬӠ1*ĈҤ,+Ӑ&%È&+.+2$ KHOA KH & KT MÁY TÍNH ---------------------------- CӜNG HÒA Xà HӜI CHӪ NGHƬA VIӊT NAM Ĉӝc lұp - Tӵ do - Hҥnh phúc 1Jj\WKiQJQăP PHIӂU CHҨM BҦO Vӊ LVTN 'jQKFKRQJ˱ͥLK˱ͣQJG̳QSK̫QEL͏Q 1. Hӑ và tên SV: NguyӉn Ĉình Tuҩn ± MSSV: 1552411 Võ Nam Hҧi ± MSSV: 1652178 Ngành (chuyên ngành): Computer Engineering 2. ĈӅ tài: Building Monitoring Tool For Core Network Using BGP Protocol. 3. Hӑ tên ngѭӡi phҧn biӋn: NguyӉn Ĉӭc Thái 4. Tәng quát vӅ bҧn thuyӃt minh: Sӕ trang: Sӕ chѭѫng: Sӕ bҧng sӕ liӋu Sӕ hình vӁ: Sӕ tài liӋu tham khҧo: Phҫn mӅm tính toán: HiӋn vұt (sҧn phҭm) 5. Tәng quát vӅ các bҧn vӁ: - Sӕ bҧn vӁ: Bҧn A1: Bҧn A2: Khә khác: - Sӕ bҧn vӁ vӁ tay Sӕ bҧn vӁ trên máy tính: 6. Nhӳng ѭu ÿiӇm chính cӫa LVTN: ‡ Students completed a monitoring tool and demonstrated it. 7. Nhӳng thiӃu sót chính cӫa LVTN: ‡ Thesis organization: o Chapter and section numbering problem, spelling problem. o Section titles do not PDWFKVHFWLRQFRQWHQWVIRUH[DPSOH³$LPDQG2EMHFWLYHV´VHFWLRQLQWKH Introduction chapter does not contain any aim and objectives. ‡ Students focused on building a monitoring tool (a software), but did not follow software development life cycle (Requirement analysis, Design, Development, Testing, 0DLQWHQDQFH« Students did not evaluate the built monitoring tool. ‡ 8. ĈӅ nghӏ: Ĉѭӧc bҧo vӋ R Bә sung thêm ÿӇ bҧo vӋ o Không ÿѭӧc bҧo vӋ o 9. 3 câu hӓi SV phҧi trҧ lӡi trѭӟc Hӝi ÿӗng: a. Briefly describe BGP protocol, and provide the contribution of your work. b. Show functionalities of the your software (monitoring tool) and describe them. c. Prove that the your software works properly. Monitoring tool for BGP Protocol Page 7 HO CHI MINH CITY UNIVERSITY OF TECHNOLOGY 10. Ĉánh giá chung (bҵng chӳ: giӓi, khá, TB): TB ĈiӇm : 5/10 Ký tên (ghi rõ hӑ tên) NguyӉn Ĉӭc Thái Monitoring tool for BGP Protocol Page 8 HO CHI MINH CITY UNIVERSITY OF TECHNOLOGY COMMITMENT The team warrants that everything presented in the report is the work of the team itself - except for the cited reference knowledge as well as the sample source code provided by the manufacturer itself, completely not copied from any other source. If the commitment is contrary to the truth, the group would like to take all responsibility before the Dean of the Faculty and the School Rector. Nguyen Dinh Tuan, Vo Nam Hai Monitoring tool for BGP Protocol Page 9 HO CHI MINH CITY UNIVERSITY OF TECHNOLOGY ACKNOWLEDGEMENT Firstly, we would like to express our sincere gratitude to our advisor PhD. Nguyen Le Duy Lai for the continuous support of our thesis, for his patience, motivation, and immense knowledge. His guidance helped us in all the time of researching and writing this thesis. We could not have imagined having a better advisor and mentor for our thesis. Besides our advisor, we would like to show gratitude to Ho Chi Minh City University of Technology for giving us the opportunity to learn great lessons of theory and practical experience. And special thanks also give to the support and kindness from lecturers in Computer Science and Engineering Department as well as Office for International Study Program - OISP of Ho Chi Minh City University of Technology. Monitoring tool for BGP Protocol Page 10 HO CHI MINH CITY UNIVERSITY OF TECHNOLOGY ABSTRACT Nowadays, the BGP protocol has become a fundamental part of the operation and performance of the Internet. As WKH ,QWHUQHW LQWHUဨGRPDLQ URXWLQJ SURWRFRO %*3 SURWRFRO KDV D QXPEHU RI vulnerabilities and weakness. Monitoring BGP is an effective way to improve the VHFXULW\RILQWHUဨGRPDLQURXWLQJ Therefore, it is obvious that we should undertake the BGP monitoring process when monitoring applications or those services that are offered being Internet the basis of its communication. TABLE OF CONTENT Monitoring tool for BGP Protocol Page 11 HO CHI MINH CITY UNIVERSITY OF TECHNOLOGY CHAPTER I: INTRODUCTION 8 I. Background 9 II. Aim and Objectives 10 1. BGP protocol 10 1.1. Introduction to the BGP protocol 10 1.2. Autonomous System (AS) 10 1.3. BGP Packet Type 12 1.4. BGP State 13 1.5. Order of routing priority in BGP: 14 1.6. Rules 15 1.7. BGP Attribute 16 2. BGP Hijacking 17 III. Thesis organization 18 CHAPTER II: BACKGROUND AND RELATED WORK 19 I. Introduce some BGP monitoring architectures and related tools: 20 1. Internet Routing Registry 20 2. Publish/subscribe model 20 3. Inter-domain routing validator 21 4. Prefix hijacking alert system 21 II. Problems that can be evaluated according to the fundamental processes of the BGP protocol: 22 1. Adjacency problems 22 2. Propagation problems 22 CHAPTER III: RESEARCH METHODS 24 I. Basic idea 25 1. Model and objective 28 2. Coordination Algorithm 29 2.1. Using CoISM 29 2.2. Route validation 30 2.3. Notification delivery Monitoring tool for BGP Protocol 35 Page 12 HO CHI MINH CITY UNIVERSITY OF TECHNOLOGY 2.4. Algorithm evaluation II. Build a monitoring tool for BGP network 38 40 1. System composition 40 2. Locating monitor for AS 42 3. Deployment 42 CHAPTER IV: IMPLEMENTATION & EVALUATION 43 I. Introduce Multi-Threaded Routing Toolkit (MRT) 44 1. Introduce 44 2. MRT Common Header 45 3. Extend Timestamp MRT Header 46 4. MRT Type 46 4.1. OSPFv2 Type 47 4.2. TABLE_DUMP Type 47 4.3. TABLE_DUMP_V2 Type 49 4.4 BGP4MP Type: 49 4.4.1. BGP4MP_STATE_CHANGE Subtype 50 4.4.2. BGP4MP_MESSAGE Subtype 51 4.4.3. BGP4MP_MESSAGE_AS4 Subtype 52 4.4.4. BGP4MP_STATE_CHANGE_AS4 Subtype 52 4.4.5. BGP4MP_MESSAGE_LOCAL Subtype 53 4.4.6. BGP4MP_MESSAGE_AS4_LOCAL Subtype 53 4.5. ISIS Type 53 4.6. OSPFv3 Type 53 5. IANA Considerations 54 6. Security Considerations 54 II. Implementation 55 CHATER V: CONCLUSION 62 I. Conclusion 63 II. Reference 64 Monitoring tool for BGP Protocol Page 13 HO CHI MINH CITY UNIVERSITY OF TECHNOLOGY LIST OF FIGURES Figure 1. Example of AS paths on transit and peering links 9 Figure 2. Example of Autonomous System Structure 11 Figure 3. Status in BGP 10 Figure 4. Synchronization Rules 15 Figure 5. Split-horizon Rule 15 Figure 6. Illustration of cooperative validation. 25 Figure 7. Illustration of AS classification. 27 Figure 8. Route validation procedure of inter-domain routing validator. 31 Figure 9. Example of human querying information. 32 Figure 10. Three classic running cases of CoISM 33 Figure 11. Routing validation procedure in cooperative information sharing mode. 35 Figure 12. Illustration of information reflection. 36 Figure 13. Composition and deployment of CoISM 41 Figure 14. MRT Common Header 45 Figure 15. Extend Timestamp MRT Header 46 Figure 16. OSPFv2 Type 47 Figure 17. TABLE_DUMP Type 48 Figure 18. BGP4MP_STATE_CHANGE Subtype 50 Figure 19. BGP4MP_MESSAGE Subtype 51 Figure 20. BGP4MP_MESSAGE_AS4 Subtype. 52 Figure 21. BGP4MP_STATE_CHANGE_AS4 Subtype. 52 Figure 22. OSPFv3 Type 53 Monitoring tool for BGP Protocol Page 14 HO CHI MINH CITY UNIVERSITY OF TECHNOLOGY LIST OF ABBREVIATIONS Acronyms Meaning BGP Border Gateway Protocol AS Autonomous System IGP protocol RIP, OSPF, EIGRP EGP protocol BGP ISP Internet Service Provider ASN Autonomous System Number TCP Transmission Control Protocol iBGP BGP is used inside an AS eBGP BGP is used between autonomous systems IRR Internet Routing Registry IRV Inter-domain routing validator PHAS Prefix hijacking alert system CoISM Cooperative information sharing model SNMP Simple Network Management Protocol MIB Management information base IETF Internet Engineering Task Force NMS Network management station OID Object identifiers UDP User Datagram Protocol PDU Protocol data units ISPCoware ISP coordination software Monitoring tool for BGP Protocol Page 15 HO CHI MINH CITY UNIVERSITY OF TECHNOLOGY CHAPTER I: INTRODUCTION Contents I. Background 9 II. Aim and Objectives 10 III. Thesis Organization 18 Monitoring tool for BGP Protocol Page 16 HO CHI MINH CITY UNIVERSITY OF TECHNOLOGY I. Background: Each Internet service provider controls prefixes, which are groups of contiguous IP addresses that can be divided for its own or customers' requirements. The BGP protocol [1] is used by the operators to connect to one other and build the Internet infrastructure. The goal of this protocol is to transmit reachability information about prefixes between two operators, who are then referred to as AS and are assigned a unique number. Each AS notifies its peer that it is able to route traffic to its prefixes. The following are the two types of interconnections: ‡3HHULQJDQDUUDQJHPHQWLQZKLFKHDFKSHHUEURDGFDVWVWKHSUHIL[HVLWPDQDJHVWRWKH others. If an ISP and a content broadcaster reach a peering arrangement, for example, their traffic will be exchanged directly; ‡Transport: a contract between a consumer and their transit provider. In actuality, the client informs the operator of its prefixes so that the latter can distribute them. In exchange, the latter promotes the remaining prefixes that make up the Internet. Figure 1. Example of AS paths on transit and peering links Each peer in a BGP interconnection assigns an AS PATH to the prefixes it broadcasts. The AS65540 router has learned the AS PATH 64510 64500 for prefix 192.0.2.0/24 in figure 1.1. A packet from the AS65540 will pass AS64510 before arriving at the AS64500 to reach IP address 192.0.2.1. The AS that manages the prefix is found on the right side of the AS path list. In reality, the AS route associated with a prefix is indicated through a BGP message of the UPDATE type. This BGP message is in charge of publicizing the routes. Monitoring tool for BGP Protocol Page 17 HO CHI MINH CITY UNIVERSITY OF TECHNOLOGY The AS65550 router has two routes to access prefix 192.0.2.0/24, as shown in Figure 1.1. One was discovered using a peering interconnection (blue), while the other was discovered through a transit interconnection (purple). In the absence of any further data, the shortest AS path is employed to decide the route. It's the peering link in this case. For prefix ads, there is no reliable authentication technique. As a result, a malicious AS can advertise a prefix that belongs to a different AS. Prefix hijacking is the term for this. Depending on the type of advertisement, the implications might range from mild to severe. The victim network, for example, may become unavailable for all or portion of the Internet. Traffic meant for the victim network may be redirected to the network that has hijacked the prefixes as a result of this sort of occurrence. II. Aim and Objectives: 1. BGP Protocol: 1.1. Introduction to the BGP protocol: BGP (Border Gateway Protocol) is a fairly complex protocol used a lot on Interfaceernet and in multinational companies, is to connect very large networks or Autonomous-Systems. Large companies can use BGP as a link between networks in different countries. The purpose of the BGP protocols is to not only find a path to a particular network, but also allow administrators to find the ASs of the Networks. Therefore, BGP is a very powerful and reliable routing protocol that makes it easy for administrators to apply routing policies.[3] 1.2. Autonomous System (AS): AS (Autonomous system) is a set of devices that share a management policy that has one or more IGPs for controlling internal routing and one EGP for offline routing (inter-domain routing). AS has numbers from 1 to 65535. There are 2 forms: - Single Home AS : AS has only one external connection. - Multi Home AS : AS has more than 1 external connection. 2 types: ‡7UDQVLW$6XVHVFRPPXQLFDWLRQIURPRQH,63WRDQRWKHU ‡1RQ± transit: AS does not transmit directly between 2 different ISPs. Monitoring tool for BGP Protocol Page 18 HO CHI MINH CITY UNIVERSITY OF TECHNOLOGY Figure 2. Example of Autonomous System Structure In the picture, our network would be one of the user networks of the AS 100 autonomous system. The ISP will then have one or more BGP routers with which it connects to other BGP routers from other AS (AS 200 and AS 300), as well as a structure composed of routers that do not necessarily apply the BGP protocol. The basic functions of a BGP router are: x 7RDGYHUWLVH\RXUVXEVFULEHUV¶QHWZRUNV x To propagate information on possible routes. x Based on this information, to choose the most convenient route for each particular traffic. ,W LV LPSRUWDQW WR QRWH WKDW %*3 URXWHUV KDYH LQIRUPDWLRQ DERXW WKHLU XVHUV¶ networks in routing tables. By default, a router must share or announce the information contained in its routing table with its neighbouring nodes. This is done based on sessions that are defined between the BGP nodes. Nodes connected by a session are called neighbouring nodes. Monitoring tool for BGP Protocol Page 19