基於O(1)流表條目實現具擴展性之服務鏈

On Scalable Service Function Chaining with O(1) Flowtable Entries

黃子銘(Tzu-Ming Huang)

指導教授 ： 曾煜棋 ； 林靖茹

國立交通大學/資訊學院/網路工程研究所/碩士(2018年)

摘要

隨著NFV與SDN的發展，網路不再單純提供戶相連接的工具，同時也能加入各種不同的服務，例如網頁應用防火牆、負載平衡等等，實際上我們常同時對一種連線使用一序列的服務，這種稱為服務鏈(Service Function Chaining)。為了在SDN網路之中使用服務鏈，過去IETF組織提出了一個Network Service Header 架構，透過在Flowtable定義一系列的轉送規則，讓管理者可以自由定義所要使用的服務，然而這個方法為了使其簡單容易實作，同時也降低了他的擴展能力，例如：我們已經定義了一個服務鏈依序為: 服務一、服務二，這時我們有個需求，交換服務的順序，這時又需要再Flowtable定義另外一系列的轉送規則，當有多樣化的服務鏈需求，Flowtable的大小將會不堪負荷。我們提出基於中國餘數定理的服務鏈方法，透過把所會經過的服務鏈經過中國餘數定理的編碼後放於封包之中，而在Flowtable僅需要儲存服務與交換器對應的質數，然後在交換的過程中透過取餘數的方法得到路徑與經過的服務，使得多樣的服務鏈需求不在需要使用大量的Flowtable entry。這裡預期服務鏈的需求不再被有限Flowtable大小所限制，而拖垮整體網路效率，有效的解決多樣的服務鏈需求所會遭遇的問題。

關鍵字

服務鏈 ； 軟體定義網路 ； 網路功能虛擬化

並列摘要

The emergence of Network Function Virtualization (NFV) enables flexible and agile service function chaining in a Software Defined Network (SDN). While this virtualization technology efficiently offers customization capability, it however comes with a cost of consuming precious TCAM resources. Due to this, the number of service chains that an SDN can support is limited by the flowtable size of a switch. To break this limitation, this paper presents CRT-Chain, a service chain forwarding protocol that requires only constant flowtable entries, regardless of the number of service chain requests. The core of CRT-Chain is an encoding mechanism that leverages Chinese Remainder Theorem (CRT) to compress the forwarding information into small labels. A switch does not need to insert forwarding rules for every service chain request, but only needs to conduct very simple modular arithmetic to extract the forwarding rules directly from CRT-Chain’s labels attached in the header. We further incorporate prime reuse and path segmentation in CRT-Chain to reduce the header size and, hence, save bandwidth consumption. Our evaluation results show that, when a chain consists of no more than 5 functions, CRT-Chain actually generates a header smaller than the legacy 32-bit header defined in IETF. By enabling prime reuse and segmentation, CRT-Chain further reduces the total signaling overhead to a level lower than the conventional scheme, showing that CRT-Chain not only enables scalable flowtable-free chaining but also improves network efficiency.

並列關鍵字

service function chaining ； software defined network ； network function virtualization

參考文獻

[1] P. Quinn, U. Elzur, and C. Pignataro, “Network Service Header (NSH),” RFC 8300, Jan. 2018. [Online]. Available: https://rfc-editor.org/rfc/rfc8300.txt

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