Re: [spring] Segment Routing in Two Dimensional IP Routing

Bo Wang <> Fri, 15 July 2022 09:25 UTC

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Date: Fri, 15 Jul 2022 17:24:51 +0800
From: Bo Wang <>
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Subject: Re: [spring] Segment Routing in Two Dimensional IP Routing
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Dear Zhenqiang,

Thanks for your professional questions. TwoD-IP routing (i.e., src-dst routing) is different from FlowSpec in the following two aspects:

1. FlowSpec is not a policy-routing protocol in essence, while TwoD-IP routing is a policy-routing protocol.

Although FlowSpec and TwoD-IP routing both use src and dst address to classify traffic, their actions on the target traffic are very different.

FlowSpec' primary goal is to mitigate the effects of DoS and DDoS attacks, and its actions mainly include dropping, rate limiting, redirect-to-VRF, reseting DSCP. Therefore, essentially, FlowSpec is not a policy-routing protocol. Instead of specifying the preference of the forwarding path for any routing node, it can only redirect the filtered traffic to one or several specific paths at most.

In contrast, TwoD-IP routing is a policy-routing protocol. It can specify the preference of the target traffic for any router node, including reachability and cost. The forwarding path is dynamically calculated according to the preference, optimization object, and constraint. TwoD-IP routing protocol has better flexibility than FlowSpec.

2. FlowSpec suffers from bad scalability if it is used to make policy-routing, where TwoD-IP routing protocol has good scalability.

FlowSpec faces the challenges of dimensional explosion if it is used to make policy-routing.

TwoD-IP routing protocol has good scalability. It addresses the explosion problem by proposing a novel forwarding table structure with a separation of TCAM and SRAM, where TCAM provides fast lookup speeds and SRMA provides large memory space.

Best Regards,
Bo Wang
Hello Bo Wang,

A SDN controller can use BGP FlowSpec to indicate the headend node to steer corresponding packets to proper SR policy. Besides source and destination IP address, other information such as source port, destination port, protocol etc, can also be specified in the BGP FlowSpec rules. 

Best Regards,
Zhenqiang Li

From: 王博
Date: 2022-07-14 10:39
Subject: [spring] Segment Routing in Two Dimensional IP Routing

We have submitted a draft “Segment Routing in Two Dimensional IP Routing” to SPRING WG. We are looking for your feedback and comments.


This draft describes an extension of SR to support TwoD-IP routing (i.e., src-dst routing) which makes forwarding decisions based on both source and destination IP addresses.

We have implemented a src-dst routing prototype based on segment routing and deployed it over CERNET (China Education and Research Network).

Bo Wang