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2017

  • in zh
  • 1 min read

面對規模化敏捷團隊的挑戰

我曾在一個使用了Nexus框架和規模化Scrum的項目上工作。一個Nexus被視為規模化Scrum中的開發單位，形成人與人之間的關聯或聯繫。軟件開發本身就是一個困難的任務，當多個團隊正在開發同一產品，並且有許多相依性時，這項任務變得更加困難。除了要面對各種角色，文物和事件，我在日常工作中遇到了三大挑戰：

  1. 唯一產品擁有者和Nexus衝刺規劃 - 根據Scrum指南，最終的決策權屬於一個單一的產品擁有者。多個團隊在Nexus衝刺規劃後進行自己的衝刺規劃。這使得產品擁有者在每個團隊的規劃中參與，如果他們同時進行，會面臨挑戰。產品擁有者不能在同一時間回答關於領域知識的問題，或為多個團隊做優先決定。如果會議時間不同步，產品擁有者就會浪費很多時間。此外，像Scrum Master，資深架構師或設計師等資源可能需要在不同的團隊之間共享。有些組織甚至設計一組產品擁有者，使決策變得複雜，因為沒有人對規模化產品具有絕對權威。

  2. 將產品待辦事項清單精煉可視化的挑戰 - 可能出現新的依賴性，需要識別並盡量減少。不幸的是，像JIRA和Trello這樣的工具並未提供簡單的方式以視覺化這些依賴性的進度或解決方法。Scrum Master可能無法充分理解複雜的技術含義，因此難以有效管理依賴性。

  3. 通過速度的角度審核Nexus Sprint - 整合工作是不可避免的，可能會影響團隊的速度。由於每個團隊都有自己的估計基準和議程，因此不清楚誰應該對重疊的工作負責。像設定伺服器、自動化測試和解決git代碼合併問題等耗時的整合任務都至關重要，但可能會拖慢團隊的進展。這些任務可能不在故事點數中完全列入，並可能在高級管理層看到速度下降時產生誤解。此外，即使每個團隊根據完成定義完成他們的故事，但在實證世界中的後期整合可能會引入新的問題，需要進行額外的跨團隊討論。

Nexus整合團隊的思維模式是答案 - 管理軟體開發的複雜性和不可預測性的最重要因素是具有正確的思維模式。會議、工具和共享工作只是更基本挑戰的症狀：讓團隊中的每一個人，包括組織領導者，理解並擁抱敏捷性。

你以前是否在規模化Scrum環境中工作過，比如SAFe或LeSS？歡迎你的評論，並期待從你的經驗中學習。

  • 11 min read

Internet Border Gateway Protocol (BGP)

This article explores the Internet Border Gateway Protocol (BGP), a standardized exterior gateway protocol designed for exchanging routing and reachability information among different Autonomous Systems (ASes) or Internet Service Providers (ISPs) on the Internet. Below, we detail the importance, capabilities, challenges, and solutions associated with this protocol.

1. The Border Gateway Protocol and its Functions

In January 1989, at the 12th Internet Engineering Task Force (IETF) meeting, Len Bosack, Kirk Lougheed, and Yakov Rekhter created BGP with the design goal of developing a protocol that could offer policy control, loop detection, and the scalability needed to support hundreds of thousands of networks through address aggregation techniques.

BGP serves as an inter-Autonomous System routing protocol, facilitating connections between ISPs. For example, Hutchison and China Mobile exchange Network Layer Reachability Information (NLRI). In an environment where the Internet lacks centralized control, these entities must exchange NLRI to integrate their autonomous networks. Each controls its own equipment and uses different intra-autonomous system routing protocols; they need to cooperate to exchange information about IP addresses associated with their customers.

The primary function of a BGP-speaking system has evolved to address this engineering and research problem: enabling information exchange between autonomous networks without centralized control. Packets sent to a service provider require table look-ups to determine their next destination, which could be on a completely different network on the other side of China. BGP serves as the foundational architecture for the global TCP/IP Internet.

Another key role of BGP is managing commercial issues. For instance, China Mobile might not want Hutchison to send excessive traffic, as it would incur additional costs. Different protocols operate within these autonomous networks, and the "best route" may differ depending on contracts and policies. BGP allows for flexibility in defining what constitutes the best route for different parties.

2. The Operations of BGP

The current version of BGP is Version 4, published as RFC 4271 in 2006. Unlike pure distance vector or link-state algorithms, BGP employs a path vector algorithm. It uses path information stored in the AS_PATH attribute to avoid traditional routing issues. Routing tables are traversed to reach the target network, providing loop avoidance. BGP also supports address aggregation, thereby significantly reducing the size of Core Internet Routing Tables.

When one Internet path fails, BGP offers network stability, enabling routers to quickly adapt and reroute packets. Each BGP router maintains a standard routing table used in conjunction with the Routing Information Base (RIB), continually updated as changes occur.

BGP updates routing table information only when changes occur. It lacks an automatic discovery mechanism, meaning peer connections must be established manually. The protocol uses an incremental update strategy to conserve bandwidth and processing power, relying on TCP for reliable transport.

3. Examples to Illustrate How ASes Can Learn About Internet Reachability

Consider a scenario with five ASes identified by unique 32-bit Autonomous System Numbers (ASNs), as shown below:

BGP enables routers within these ASes to learn multiple paths via internal and external BGP speakers. It selects the best path and installs it in the RIB. When a customer in the AS104 network wants to send data to the AS100 network, BGP helps routers within AS104 decide which path to take, updating reachability information accordingly.

BGP also provides for the management of trust and distrust among different service providers and is outlined in RFC 4271. It allows networks with common routing policies to be uniquely identified and is widely used in Internet backbones.

BGP makes best-path decisions based on current reachability, hop counts, and other path attributes. It can be configured to communicate an organization's routing preferences and has a mechanism for defining arbitrary tags, known as communities, to control route advertisement behavior by mutual agreement among peers.

4. BGP Packet Formats and Field Functions

BGP messages are transmitted over TCP connections. A message undergoes processing only after it is completely received. The maximum message size is 4096 octets, whereas the smallest permissible message consists of a 19-octet header without any data. Below, we highlight the functions of some of the fields:

4.1 Message Header Format

Marker: This 16-octet field is included for compatibility and must be set to all ones.

Length: This 2-octet unsigned integer represents the total length of the message, including the header, in octets. It helps in locating the Marker field of the next message in the TCP stream. The field value must always be greater than 19 and less than 4096. Padding with extra data after the message is prohibited; thus, the field must contain the smallest required value.

Type: This 1-octet unsigned integer specifies the message's type code. The type codes are: 1 — Open, 2 — Update, 3 — Notification, 4 — Keepalive.

4.2 Open Message Format

After establishing a TCP connection, both sides send an Open message as the first message. If the Open message is accepted, a Keepalive message confirming the Open is sent in response.

Version: This 1-octet unsigned integer indicates the protocol version number of the message.

My Autonomous System: This 2-octet unsigned integer specifies the sender's AS number.

Hold Time: This 2-octet unsigned integer suggests a value for the Hold Timer in seconds. Upon receiving an Open message, a BGP speaker calculates the hold timer by taking the lesser of its configured hold time and the received hold time. This time must be either 0 or at least 3 seconds. Connections may be rejected based on this time value.

BGP Identifier: This 4-octet unsigned integer identifies the sender's BGP Identifier. The value is determined at startup and remains consistent across all local interfaces and BGP peers.

Opt Param Len: This 1-octet unsigned integer shows the total length of the Optional Parameters field in octets. A zero value indicates that no Optional Parameters are present.

Optional Parameters (variable): This field contains a list of optional parameters, each encoded as follows:

  • Parameter Type: 1-octet field identifying individual parameters.
  • Parameter Length: 1-octet field specifying the length of the Parameter Value field in octets.
  • Parameter Value (variable): Interpreted based on the Parameter Type field's value.

The Open message's minimum length, including the header, is 29 octets.

4.3 Update Message Format

This format is used to exchange routing information between BGP peers, helping to build a graph that represents the relationships among various Autonomous Systems (AS). It identifies and eliminates routing loops and other anomalies in inter-AS routing.

An Update message serves to advertise feasible routes with common path attributes or to withdraw multiple unfeasible routes. It may both advertise a feasible route and withdraw multiple unfeasible routes simultaneously.

Withdrawn Routes Length (2 octets): Indicates the total length of the Withdrawn Routes fields; a value of 0 implies no routes are being withdrawn.

Withdrawn Routes (variable): Contains a list of IP address prefixes of the routes being withdrawn.

Length (1 octet): Specifies the length, in bits, of the IP address prefix; a value of 0 matches all IP addresses.

Prefix (variable): Contains an IP address prefix and the minimum number of trailing bits needed to align the field's end on an octet boundary.

Total Path Attributes Length (2 octets): Indicates the total length of the Path Attributes fields in octets. A value of zero signifies that neither the NLRI nor the Path Attribute fields are present.

Path Attributes (variable): A triplet consisting of <attribute type, attribute length, attribute value>. The attribute type is a 2-octet field that includes:

  • Attr. Flags: Various bits are used for different purposes, such as optional bit, transitive bit, partial bit, and Extended Length bit.
  • Attr. Type Code: Codes like Origin, AS_PATH, NEXT_HOP, MULTI_EXIT_DISC, LOCAL_PREF, ATOMIC_AGGREGATE, and AGGREGATOR specify different types of path attributes.

Network Layer Reachability Information (variable): Contains a list of IP address prefixes. Its length is not explicitly encoded but can be calculated using the formula:

( \text{Updated message length} - 23 - \text{Total Path Attributes Length} - \text{Withdrawn Routes Length} )

  • "Updated message length" is the value encoded in the fixed-size BGP header.
  • "Total Path Attributes Length" and "Withdrawn Routes Length" are variable parts of the update message.
  • 23 is the combined length of the fixed-size BGP header, the Total Path Attribute Length field, and the Withdrawn Routes Length field.

The reachability information is encoded as one or more 2-tuples, each having:

Length (1 octet): Indicates the length, in bits, of the IP address prefix. A value of 0 matches all IP addresses, with the prefix itself consisting of zero octets.

4. Packet Formats in BGP and Highlighting Functions of Some Fields

BGP messages are sent over TCP connections. A message is processed only after it has been entirely received. The maximum message size is 4096 octets, while the smallest permissible message consists of a 19-octet header without a data portion. Below, we highlight the functions of some fields:

4.1 Message Header Format
  • Marker: A 16-octet field included for compatibility, which must be set to all ones.

  • Length: A 2-octet unsigned integer that indicates the total length of the message, including the header, in octets. This helps locate the Marker field of the next message in the TCP stream. The value must always be greater than 19 and smaller than 4096. Padding with extra data after the message is not allowed.

  • Type: A 1-octet unsigned integer indicating the message's type code. The type codes are: 1—Open, 2—Update, 3—Notification, 4—Keepalive.

4.2 Open Message Format

After establishing a TCP connection, the first message each side sends is an Open message. If the Open message is acceptable, a Keepalive message confirming the Open is sent in return.

  • Version: A 1-octet unsigned integer that indicates the message's protocol version number.

  • My Autonomous System: A 2-octet unsigned integer indicating the sender's AS number.

  • Hold Time: A 2-octet unsigned integer indicating the proposed value for the Hold Timer in seconds. Upon receiving an Open message, a BGP speaker must calculate the value of the Hold Timer using the lesser of its configured hold time and the hold time received. The Hold Timer value must be either 0 or at least 3 seconds.

  • BGP Identifier: A 4-octet unsigned integer indicating the sender's BGP Identifier, set to an IP address assigned to that BGP speaker.

  • Opt Param Len: A 1-octet unsigned integer indicating the total length of the Optional Parameters field in octets.

  • Optional Parameters (variable): A list of optional parameters, each encoded as a triplet: Parameter Type, Parameter Length, Parameter Value.

The minimum length of the Open message, including the header, is 29 octets.

4.3 Update Message Format

This message type transfers routing information between BGP peers. Update messages can advertise feasible routes or withdraw multiple unfeasible routes. An Update message can simultaneously advertise a feasible route and withdraw multiple unfeasible routes.

  • Withdrawn Routes Length (2 octets): Indicates the total length of Withdrawn Routes fields. A value of 0 means no routes are being withdrawn.

  • Withdrawn Routes (variable): Contains a list of IP address prefixes for routes being withdrawn.

  • Length (1 octet): Indicates the length in bits of the IP address prefix. A 0 means a prefix matching all IP addresses.

  • Prefix (variable): Contains an IP address prefix, followed by enough trailing bits to ensure the field ends on an octet boundary.

  • Total Path Attributes Length (2 octets): Indicates the total length of the Path Attributes fields in octets. A value of zero means that neither the NLRI nor the Path Attribute field is present.

  • Path Attributes (variable): A triple consisting of attribute type, attribute length, and attribute value.

Additional details are provided for individual attribute types like Attr. Flags, Attr. Type Code, and Network Layer Reachability Information.

The minimum length of an Update message is 23 octets: 19 for the fixed header + 2 for the withdrawn routes length + 2 for the total path attribute length.

4.4 Keepalive Message Format

BGP doesn't use any TCP-based keep-alive mechanisms to determine if peers are reachable. Instead, Keepalive messages are exchanged frequently enough to prevent the Hold Timer from expiring. The maximum reasonable time between Keepalive messages is one-third of the Hold Time interval. Keepalive messages should not be sent more often than once per second.

4.5 Notification Message Format

A Notification message is sent when an error is detected. The BGP connection is immediately closed after sending this message. The Notification message includes the following fields:

  • Error Code (1-octet): Indicates the type of error.

  • Error Subcode (1-octet): Provides additional information about the error.

  • Data (variable): Used for diagnosing the reason for the notification.

The minimum length of a Notification message is 21 octets.

5. Instability Problems in BGP and Proposed Solutions

Instability is defined as rapid changes in network reachability and topology information. Various issues such as software bugs, TCP attacks, or congestion can lead to loss of service, wasteful utilization of network resources, and degraded performance for Quality of Service (QoS)-demanding applications.

One classic problem in BGP is known as the "black-hole phenomenon." An incorrect manual configuration can cause a BGP router to improperly announce routes through its Autonomous System (AS), leading other BGP routers to update their routing tables accordingly. This results in a massive amount of traffic being forwarded to that AS, causing significant packet loss and ultimately, network congestion.

Another symptom of instability is the disappearance of an existing route, termed "flapping" if the route reappears shortly thereafter. Flapping occurs when a router sends a routing update and then withdraws it shortly afterward. This forces peer routers to propagate and then withdraw updates, affecting the performance of the network and potentially causing transient loss of connectivity.

Internal congestion within an AS can also lead to instability by causing the TCP connections between two BGP routers to time out.

A robust BGP implementation should ensure that instability in a subset of routes does not affect the router's advertisements or forwarding of stable routes. Instability should not be caused by peers with varying levels of stability or different processing speeds. The impact of unstable peers on the network's convergence time should be limited.

One proposed solution is route flap damping. This prevents heavy processing loads on routers, which could otherwise delay updates. Route flaps are exponentially decayed to mitigate denial-of-service attacks.

6. Security Concerns in BGP and Enhancements

BGP is susceptible to various attacks due to the lack of message integrity and authentication. Communications between BGP peers are vulnerable to both active and passive wiretapping. Unauthorized access to a router can result in the alteration of its software, configuration information, and routing databases, transforming the router into a hostile entity.

Another significant vulnerability stems from the underlying transport protocol, TCP. BGP is susceptible to the same types of attacks that plague TCP, such as SYN flooding, which can exhaust server resources like memory and bandwidth.

Attackers can also disrupt TCP connections to impersonate legitimate peer routers. Since the RFC-defined mechanism does not provide peer-entity authentication, these connections may be susceptible to replay attacks, leading to the delivery of spoofed BGP messages.

Attackers could also generate false route flaps to cause a victim’s prefix to be damped. To mitigate this, parameters should be adjusted to more conservative values, reducing risk and partially countering false flap attacks.

To improve security further, each protected peer should have a unique key for communication. Using the same key for multiple peers increases the risk of compromising one router and adversely affecting others.

Lastly, keys used for MAC computation should be rotated periodically, ideally every 90 days, to minimize the risks associated with key compromise or successful cryptanalytic attacks. Additionally, keys should be selected to be difficult for attackers to guess.

  • in podcast
  • 2 min read

Internet Border Gateway Protocol (BGP)

Welcome back to another episode of Continuous Improvement, the podcast where we explore ways to enhance our knowledge and skills. I'm your host, Victor, and today, we're diving into the fascinating world of the Internet Border Gateway Protocol, commonly known as BGP.

BGP, a standardized exterior gateway protocol, plays a crucial role in exchanging routing and reachability information among different Autonomous Systems or Internet Service Providers on the Internet. It enables the integration of autonomous networks and facilitates connections between ISPs.

BGP was introduced back in 1989 with the goal of developing a protocol that provides policy control, loop detection, and scalability. Today, it serves as the foundational architecture of the global TCP/IP Internet.

One of the primary functions of BGP is enabling information exchange between autonomous networks without centralized control. This allows service providers to determine the best route for their customers' data, considering factors such as reachability, hop counts, and agreements with other providers.

BGP also plays a significant role in managing commercial issues among different service providers. For instance, ISPs may want to control excessive traffic to avoid additional costs, or they may have different routing policies based on contracts and agreements. BGP provides the flexibility to define the best routes according to these commercial considerations.

So, how does BGP work? Well, the current version of BGP is Version 4, published as RFC 4271 in 2006. Unlike traditional routing algorithms, BGP employs a path vector algorithm and uses path information stored in the AS_PATH attribute to avoid routing issues and loop avoidance.

BGP updates routing table information only when changes occur, ensuring efficient use of bandwidth and processing power. However, it lacks an automatic discovery mechanism, so peer connections must be established manually. These connections are maintained using TCP for reliable transport.

Let's take a closer look at the different BGP packet formats and their field functions. BGP messages are transmitted over TCP connections, and each message is processed only after it has been completely received.

The BGP message header format consists of fields such as Marker, Length, and Type. The Marker field is included for compatibility, while the Length field indicates the total length of the message, including the header. The Type field specifies the message's type code, such as Open, Update, Notification, or Keepalive.

The

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  • in zh
  • 2 min read

網際網路邊界閘道協定（BGP）

本文章探討網際網路邊界閘道協定（BGP），這是一種標準化的外部閘道協定，設計用於在互聯網上的不同自治系統（ASes）或網際網路服務提供商（ISP）之間交換路由和可達性資訊。以下，我們詳細介紹了與此協定相關的重要性、能力、挑戰和解決方案。

1. 邊界閘道協定及其功能

1989年1月，在第12次網際網路工程任務組（IETF）會議上，Len Bosack、Kirk Lougheed和Yakov Rekhter創造了BGP，其設計目標是開發一種能夠提供政策控制、迴路檢測以及通過地址聚合技術支持數十萬個網路的協定。

BGP作為一種自治系統間的路由協定，便利了ISPs之間的連接。例如，和記黃埔和中國移動交換網路層可達性資訊（NLRI）。在互聯網缺乏集中控制的環境中，這些實體必須交換NLRI以整合他們的自治網路。每一個都控制自己的設備並使用不同的自治系統內部路由協定；他們需要合作來交換與他們的客戶相關的IP地址資訊。

一個使用 BGP 的系統的主要功能已演變為解決這個工程和研究問題：使自治網路之間能交換資訊，而無需集中式控制。發送到服務提供商的數據包需要進行查找才能決定下一個目的地，可能是中國另一邊的完全不同的網絡。BGP是全球 TCP/IP 網路的基本架構。

BGP的另一個重要角色是管理商業問題。例如，中國移動可能不希望和記黃埔發送過量的流量，因為這將增加額外的成本。這些自治網絡內部運行著不同的協定，「最佳路徑」可能會根據合同和政策而有所不同。BGP提供了靈活性，可以定義對不同方來說什麼是最佳路徑。

2. BGP的運作

BGP的當前版本是版本4，於2006年以RFC 4271的形式出版。BGP使用一種路徑向量算法，而不是純粹的距向量或連接狀態算法。它使用存儲在AS_PATH屬性中的路徑資訊來避免傳統路由問題。路由表被遍歷以到達目標網絡，從而提供迴路避免。BGP還支持地址聚合，從而大大減少了核心互聯網路由表的大小。

當一條互聯網路徑失效時，BGP提供了網路穩定性，使路由器能夠快速適應和重新路由數據包。每個BGP路由器都維護一個標準路由表，該表與路由資訊庫（RIB）一起使用，並在變化發生時不斷更新。

BGP只在變化發生時更新路由表資訊。它缺少自動發現機制，這意味著必須手動建立對等連接。該協定使用一種增量更新策略，以節省帶寬和處理能力，依賴TCP來提供可靠的傳輸。

3. 舉例說明ASes如何了解網際網路的可達性

可以假設我們有五個由唯一的32位自治系統號（ASN）標識的ASes，如下所示：

BGP允許這些ASes內的路由器通過內部和外部的BGP說明者來學習多條路徑。它選擇最佳路徑並將其安裝在RIB中。當AS104網絡中的一個客戶希望將數據發送到AS100網絡時，BGP幫助AS104內的路由器決定哪條路徑走，並相應地更新可達性資訊。

BGP還提供了對不同服務提供商之間的信任和不信任的管理，並且在RFC 4271中進行了描述。它允許具有共同路由政策的網絡能夠被唯一的標識，並且被廣泛地用在互聯網的骨幹網絡上。

BGP確定最佳路徑的決策依賴於當前的可達性、跳數和其他路徑屬性。它可以被配置為告知一個組織的路由偏好，並且有一個定義任意標簽（即社區）的機制，以控制經過對等體之間的共同協議的路由廣告行為。

4. BGP包格式和欄位函數

BGP消息通過TCP連接進行傳輸。只有在消息完全接收後才進行處理。消息的最大尺寸為4096字節，而最小允許的消息由一個19字節的頭部組成，而沒有任何數據。以下我們突出了一些欄位的功能：

4.1 消息頭部格式

標記：這是一個16字節的欄位，用於相容性，必須設置為全1。

長度：這是一個2字節的無符號整數，表示消息中包括頭部在內的總長度，以字節為單位。它有助於在TCP流中找到下一條消息的標記欄位。欄位值必須始終大於19並小於4096。消息後面不能填充額外的數據，因此該欄位必須包含最小的必需值。

類型：這是一個1字節的無符號整數，指定消息的類型代碼。類型代碼有：1-Open、2-Update、3-Notification、4-Keepalive。

4.2 Open消息格式

建立TCP連接後，雙方首先發送的消息是Open消息。如果Open消息是可以接受的，則回發送一個確認Open的Keepalive消息。

版本：這是一個1字節的無符號整數，表示消息的協定版本號。

我的自治系統：這是一個2字節的無符號整數，指定發件者的AS號碼。

保持時間：這是一個2字節的無符號整數，表明在秒中的保持計時器的值。在收到一條Open消息後，BGP講話者透過取其配置的保持時間和收到的保持時間中的較小者來計算保持計時器。此時間必須為0 或 至少為3秒。可能會根據此時間值拒絕連接。

BGP標識符：這是一個4字節的無符號整數，標識發件人的BGP標識符。該值在啟動時確定，並在所有本地接口與BGP對等方保持一致。

Opt Param Len：這是一個1字節的無符號整數，顯示可選引數欄位的總長度，以字節為單位。零值表示沒有提供可選引數。

可選參數（變量）：此欄位包含一個參數列表，每個參數分別編碼如下：

  • 參數類型：1字節欄位用於識別個別參數。
  • 參數長度：1字節欄位指定參數值欄位的長度，以字節為單位。
  • 參數值（變量）：根據參數類型欄位的值來詮釋。

Open消息的最小長度（包括頭部）為29個字節。

4.3 Update消息格式

此格式用於在BGP對等體之間交換路由資訊，有助於構建表示各種自治系統（AS）之間關係的圖。它通過識別並消除路由迴路和其他的自治系統間路由異常。

Update消息可以用來廣告具有共同路徑屬性的可行路徑，或撤銷多條不可行的路徑。它可以在同時廣告一條可行路徑和撤銷多條不可行路徑。

撤銷的路徑長度（2個字節）：指示撤銷路徑欄位的總長度；值為0表示沒有路徑被撤銷。

撤銷的路徑（變量）：包含被撤銷路徑的IP地址前綴的列表。

長度（1個字節）：以位為單位指定IP地址前綴的長度；值為0與所有IP地址的匹配。

前綴（變量）：包含一個IP地址前綴，以及為在字節邊界上對齊欄位結尾需要的最少尾隨位數。

總路徑屬性長度（2個字節）：指示以字節為單位的路徑屬性欄位的總長度。值為0表示沒有 NLRI 或 path 屬性欄位存在。

路經屬性（可變）：由<屬性類型，屬性長度，屬性值>組成的 3 元組。 屬性類型是一個 2 字節的欄位，其中包括：

  • 屬性標誌：各種位用於不同的目的，如選擇位、轉移位、部分位和擴展長度位。
  • 屬性類型代碼：如原始碼、AS_PATH、NEXT_HOP、MULTI_EXIT_DISC、LOCAL_PREF、原子聚合和聚合器指定了不同類型的路徑屬性。

網路層可達性資訊（變量）：包含一個 IP 地址前綴的列表。其長度並不直接編碼，但可以使用以下式子計算：

( \text{更新消息長度} - 23 - \text{路徑屬性長度總計} - \text{撤銷路徑長度} )

  • 「更新消息長度」是固定大小的BGP首部中編碼的值。
  • 「路徑屬性長度總計」和「撤銷路徑長度」是更新消息的變動部分。
  • 23是固定大小的BGP頭部、路徑屬性長度和撤銷路徑長度的總和。

達性資訊是以一個或多個2元組編碼，每個都有：

長度（1個字節）：以位為單位指出 IP 地址前綴的長度。值為0與所有 IP 地址的匹配，自身前綴包含零個字節。

4. 在BGP中的包格式及突出一些欄位的功能

BGP消息通過TCP連線發送。僅在接收到整個消息後才進行處理。消息的最大尺寸為4096個八位組，而最小合理的消息由19個八位組的標頭組成，不含任何數據。以下，我們突出了某些欄位的功能：

4.1 消息標頭格式

  • 標記：這是一個16個八位組的欄位，為了與過去的協議版本相容，必須設定為全為一。

  • 長度：這是一個2個八位組的無號整數，表示包含標頭在內的消息的總長度，單位為八位組。須以此欄位的值間接找出TCP資料流中下一個消息的標記欄位。欄位值必須永遠大於19且小於4096。禁止在消息後面填充額外的數據，因此這個欄位的值必須只含最小所需的值。

  • 類型：這是一個單個八位組無號整數，指定了消息的類型碼。類型碼為：1-Open、2-Update、3-Notification、4-Keepalive。

4.2 Open消息格式

在建立TCP連線後，每一方首先發送的消息是一條open消息。如果收到的open消息可以被接受，就會回應一條確認接收open消息的keepalive消息。

  • 版本：這是一個單個八位組無號整數，顯示了消息的協議版本號。

  • 我的自治系統：這是一個2個八位組無號整數，表明了發送者的AS編號。

  • 保持時間：這是一個2個八位組無號整數，表示了保持計時器的值建議，單位為秒。在收到open消息時，一個BGP有聲人應當通過取配置的保持時間和已接收到的保持時間中的最小值來計算保持計時器。此時間必

  • 2 min read

Pseudo-Scrum - A Hybrid of Waterfall and Agile

I have something to tell you: you're not truly agile. You may have gone through the motions, performing all the scrum rituals like stand-ups, demos, and retrospectives. You may even have all the requisite tools like JIRA, user stories, and a scrum board. However, if the mindset isn't right, something fundamental is still missing. Here's why:

You Have a Detailed Plan

You're adhering to a strict year-long deadline. Scrum teams calculate velocity based on estimates made during sprint planning. So, how can you expect the scrum team to align with top management's best guesses? When the roadmap is fixed, the scope is unchanging, and the release plan is impractical, you're actually following a waterfall model.

Absence of a True Scrum Master

You may have a Scrum Master on your org chart, but what's their actual role? Often, the person isn't a full-time Scrum Master but a project manager, product owner, or senior developer who isn't wholly committed to the role. When the Scrum Master is juggling multiple responsibilities, things start to derail. Even if you do have a dedicated Scrum Master, they may not be able to address real impediments due to technical complexities or constraints beyond their job description.

No Designated Product Owner

Someone needs to be in charge of the product, but often that person is preoccupied with other priorities. Without a clear vision and product ownership, feature development may go awry. This is particularly true when requirements are dictated by external senior directors, leading to wasted development efforts. While the product owner should make these decisions, few are willing to take the risks and many are unsure of what they actually want.

Lack of a Budgeting Strategy

Story points are not a substitute for budgeting. When you manipulate estimates to secure more funds and time, or negotiate downward to meet budget constraints, you lose sight of the team's true velocity. Traditional accounting methods are also not compatible with agile development. Skimping on budget often leads to team burnout without achieving the intended outcomes.

My Take on the Agile Manifesto

Here's how I interpret the Agile Manifesto in my own words: Prioritize responsiveness to change over adhering to a strict roadmap set by senior management. Value individuals and interactions over office politics. Emphasize working software over endless, pointless meetings. Favor customer collaboration over budget negotiations. Achieving this is no simple task, but it's the only way for bureaucratic organizations to adapt and thrive in the digital age.

  • in podcast
  • 2 min read

Pseudo-Scrum - A Hybrid of Waterfall and Agile

Welcome to Continuous Improvement, the podcast where we explore the challenges of achieving true agility in today's organizations. I'm your host, Victor, and in today's episode, we're going to dive into why you might not be as agile as you think you are.

Picture this scenario: you've implemented all the scrum rituals, you have the tools and processes in place, but if the mindset isn't right, something fundamental is still missing. So, let's break it down, starting with the first reason why you might not be truly agile.

Reason number one: you have a detailed plan. Now, don't get me wrong, planning plays an essential role, but when the roadmap is fixed, the scope is unchanging, and the release plan is impractical, you're actually following a waterfall model. Scrum teams need the flexibility to adapt to change and align with top management's evolving priorities.

Moving on to reason number two: the absence of a true Scrum Master. Sure, you may have someone with the title on your org chart, but what's their actual role? Often, the Scrum Master is juggling multiple responsibilities, which leads to a lack of focus and derails the agile process. Even if you do have a dedicated Scrum Master, they may not have the authority or ability to address real impediments, hindering the team's progress.

Reason number three: no designated Product Owner. Someone needs to be in charge of the product, providing a clear vision and taking ownership. However, many times, the person in this role is preoccupied with other priorities, causing feature development to go off track. It's essential to have a Product Owner who can make informed decisions and guide the team effectively.

Now let's talk about reason number four: the lack of a budgeting strategy. Story points are not a substitute for proper budgeting. Manipulating estimates to secure more funds or negotiating downward to meet budget constraints only distorts the team's true velocity. Traditional accounting methods often clash with agile development, leading to burnout and compromised outcomes.

Finally, let me share my take on the Agile Manifesto. Prioritize responsiveness to change over adhering to a strict roadmap set by senior management. Value individuals and interactions over office politics. Emphasize working software over endless, pointless meetings. And most importantly, favor customer collaboration over budget negotiations. It's not an easy task, but it's the only way for bureaucratic organizations to adapt and thrive in the digital age.

And that's a wrap for today's episode of Continuous Improvement. I hope you've gained valuable insights into the key factors that may be hindering your organization's agility. Remember, it's not just about going through the motions, but embracing the mindset of continuous improvement.

Join me next time as we explore strategies to overcome these challenges and truly unlock the power of agility within your organization. Until then, keep striving for progress and continuous improvement.

  • in zh
  • 1 min read

偽Scrum - 瀑布式和敏捷的混合體

我有些事情要告訴你：你並非真正的敏捷。你可能已經完成了所有的 Scrum 儀式，如站立會議、示範和檢討。你甚至可能有所有必要的工具，如JIRA、使用者故事和Scrum看板。然而，如果心態不正確，那麼某些基本的東西仍然缺失。以下是原因：

你有一個詳細的計劃

你正在堅持嚴格的一年期限。Scrum團隊根據在衝刺計劃期間做出的估算來計算速度。那麼，你怎麼能期待Scrum團隊與高層管理的最佳猜測相符呢？當路線圖是固定的，範圍不變，並且發布計劃不切實際時，你實際上正在遵循瀑布模型。

真正的Scrum Master缺席

你的組織圖上可能有一個Scrum Master，但他們的實際角色是什麼？通常，這個人不是全職的Scrum Master，而是一個項目經理、產品擁有者或者資深開發者，他們並未全心投入這個角色。當Scrum Master兼顧多項責任時，事情就開始出軌。即使你有一個專門的Scrum Master，他們可能也無法解決由於技術複雜性或超出他們工作職責的限制所帶來的實際障礙。

沒有指定的產品擁有者

需要有人負責產品，但通常這個人會被其他優先事項所佔據。如果沒有明確的視野和產品所有權，特性開發可能會出錯。當要求由外部高級主管指導時，這一點尤其正確，導致開發努力被浪費。雖然產品擁有者應該做出這些決定，但很少有人願意冒這些風險，許多人對他們實際想要什麼並不確定。

缺乏預算策略

故事點並不能替代預算。當你操縱估算來獲得更多的資金和時間，或者為了符合預算限制而向下談判，你就會對團隊的真實速度失去了視覺。傳統的會計方法也與敏捷開發不兼容。在預算上吝嗇往往會導致團隊燒休息，而不達到預期的結果。

我對敏捷宣言的看法

以下是我用自己的話來解釋敏捷宣言：把對變化的反應性放在遵循高級管理層設定的嚴格路線圖之上。尊重個人和互動超過辦公室政治。強調工作軟體超過無休止，毫無意義的會議。偏愛客戶合作超過預算談判。實現這一點並非易事，但對於官僚機構來說，這是在數位時代適應和繁榮的唯一途徑。

  • 3 min read

Deploying a Koa.js Application to an AWS EC2 Ubuntu Instance

I am developing an application using Koa.js, a new web framework created by the team behind Express. In this step-by-step tutorial, I'll guide you through deploying a Koa.js application on an Amazon Web Services (AWS) Ubuntu server.

Launching the Ubuntu Instance on AWS

First, launch an Ubuntu instance on AWS. You'll need to modify the security group settings.

Security Group Settings

If you don't make these changes, attempting to access the public domain in a browser will result in a "Connecting" state until it times out, rendering the site unreachable.

Site Unreachable

By default, the launch wizard only enables SSH.

SSH Only

Click the "Edit" button to add inbound rules for HTTP port 80 and HTTPS port 443.

Edit Inbound Rules

Installing Node.js

SSH into your instance and install Node.js according to the official documentation:

curl -sL https://deb.nodesource.com/setup_6.x | sudo -E bash -
sudo apt-get install -y nodejs

Setting Up Nginx as a Reverse Proxy Server

Next, install Nginx:

sudo apt-get update
sudo apt-get install nginx

Open the configuration file and make the following edits. Don't forget the semicolons:

server {
    listen 80 default_server;
    listen [::]:80 default_server;

    root /var/www/yourApp;

    location / {
        proxy_pass http://localhost:3000;
        proxy_http_version 1.1;
        proxy_set_header Upgrade $http_upgrade;
        proxy_set_header Connection 'upgrade';
        proxy_set_header Host $host;
        proxy_cache_bypass $http_upgrade;
    }
}

Save the file and restart the Nginx service:

sudo systemctl restart nginx

Deploying Your Application

Clone your Git repository into the /var/www/yourApp directory. You'll likely encounter a "Permission Denied" error, so change the ownership of the folder:

sudo chown -R ubuntu /var/www

Create a simple app.js to run your server:

var koa = require("koa")
var app = koa()

// logger
app.use(function* (next) {
  var start = new Date()
  yield next
  var ms = new Date() - start
  console.log("%s %s - %s", this.method, this.url, ms)
})

// response
app.use(function* () {
  this.body = "Hello World"
})

app.listen(3000)

Start the server:

node app.js

Open your browser and navigate to your public domain. You should see your Koa.js application running.

App Running

Done! Feel free to leave a comment below if you have any questions. :)

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  • 3 min read

Deploying a Koa.js Application to an AWS EC2 Ubuntu Instance

Hello everyone, and welcome to "Continuous Improvement," the podcast where we explore different strategies and techniques for improving our skills and knowledge in the technology world. I'm your host, Victor, and in today's episode, we're going to dive into deploying a Koa.js application on an Amazon Web Services (AWS) Ubuntu server.

But before we begin, a quick reminder to subscribe to our podcast on your favorite platform and follow us on social media to stay updated on all our latest episodes. Alright, let's get started!

The first step in deploying our Koa.js application is to launch an Ubuntu instance on AWS. Now, it's important to modify the security group settings to ensure our application is accessible.

As you can see in the images provided in the blog post, it is necessary to add inbound rules for HTTP port 80 and HTTPS port 443. Without these changes, accessing the public domain in a browser would result in a "Connecting" state, eventually timing out and rendering the site unreachable.

Now that we have our Ubuntu instance set up, the next step is to install Node.js, the runtime environment for our Koa.js application. SSH into your instance and follow the official documentation instructions to install Node.js.

With Node.js successfully installed, we now move on to setting up Nginx as a reverse proxy server. Nginx will help us route traffic to our Koa.js application.

First, we need to install Nginx by running the appropriate commands. Once that's done, we'll open the Nginx configuration file and make the necessary edits, including adding the server block with the reverse proxy settings. Don't forget those semicolons!

After saving the configuration file, we need to restart the Nginx service to apply the changes.

Now that our server and reverse proxy are set up, it's time to deploy our Koa.js application. Clone your Git repository into the /var/www/yourApp directory on the Ubuntu instance. Keep in mind that you may encounter a "Permission Denied" error, but it can be easily fixed by changing the ownership of the folder.

Great! With the application files in place, it's time to create a simple app.js file to run our Koa.js server. The code in this file sets up a basic Koa.js server with a logger and a response that says "Hello World".

We're almost there! Just a few more steps. Start the server by running the node app.js command in the terminal.

And finally, open your browser and navigate to your public domain. If everything was done correctly, you should now see your Koa.js application running.

Congratulations! You've successfully deployed your Koa.js application on an AWS Ubuntu server. I hope this step-by-step guide has been helpful to you. If you have any questions or need further assistance, please feel free to leave a comment on the blog post.

That wraps up this episode of "Continuous Improvement." I hope you found the information valuable and that it inspires you to continue expanding your skills and knowledge. Don't forget to subscribe to our podcast and follow us on social media for more episodes like this one. Thanks for tuning in, and until next time, keep improving!

heroImage: '/2017-01-07.png'---

  • in zh
  • 2 min read

將 Koa.js 應用程式部署至 AWS EC2 Ubuntu 實例

我正在使用 Koa.js 開發一個應用程式，這是一個由 Express 團隊創建的新網頁框架。在這個逐步教學中，我將指導您如何在 Amazon Web Services (AWS) Ubuntu 伺服器上部署 Koa.js 應用程式。

在 AWS 上啟動 Ubuntu 實例

首先，在 AWS 上啟動一個 Ubuntu 實例。您需要修改安全組設定。

Security Group Settings

如果您沒有進行這些更改，試圖在瀏覽器中訪問公共域將導致“連接”狀態，直到超時，導致無法訪問網站。

Site Unreachable

默認情況下，啟動嚮導僅啟用 SSH。

SSH Only

點擊“編輯”按鈕以添加適用於 HTTP 端口 80 和 HTTPS 端口 443 的入站規則。

Edit Inbound Rules

安裝 Node.js

通過 SSH 登入您的實例並根據官方文檔安裝 Node.js：

curl -sL https://deb.nodesource.com/setup_6.x | sudo -E bash -
sudo apt-get install -y nodejs

設置 Nginx 作為反向代理伺服器

接下來，安裝 Nginx：

sudo apt-get update
sudo apt-get install nginx

打開配置文件並進行以下編輯。別忘了分號：

server {
    listen 80 default_server;
    listen [::]:80 default_server;

    root /var/www/yourApp;

    location / {
        proxy_pass http://localhost:3000;
        proxy_http_version 1.1;
        proxy_set_header Upgrade $http_upgrade;
        proxy_set_header Connection 'upgrade';
        proxy_set_header Host $host;
        proxy_cache_bypass $http_upgrade;
    }
}

保存文件並重新啟動 Nginx 服務：

sudo systemctl restart nginx

部署您的應用程式

將您的 Git 存儲庫克隆到 /var/www/yourApp 目錄。您可能會遇到“Permission Denied”錯誤，所以更改文件夾的所有權：

sudo chown -R ubuntu /var/www

創建一個簡單的 app.js 來運行您的伺服器：

var koa = require("koa")
var app = koa()

// logger
app.use(function* (next) {
  var start = new Date()
  yield next
  var ms = new Date() - start
  console.log("%s %s - %s", this.method, this.url, ms)
})

// response
app.use(function* () {
  this.body = "Hello World"
})

app.listen(3000)

啟動伺服器：

node app.js

打開您的瀏覽器並導航到您的公共域。您應該看到您的 Koa.js 應用程式正在運行。

App Running

完成！如果您有任何問題，請隨時在下面留言。:)