SafeGuard

SafeGuard is a novel intra-domain routing system which achieves consistent forwarding without sacrificing network's responsiveness to dynamic changes. In SafeGuard, each packet carries its path cost as a lightweight safeguard information to detect and repair routing inconsistencies.

• Routing inconsistency is the root cause of many routing anomalies such as transient forwarding loops and routing black holes.
• Existing approaches (e.g., Consensus Routing and Ordered FIB update) ensure consistency by delaying routing convergence, which sacrifices network's responsiveness to dynamic changes.
• It is impossible to detect inconsistency if packets do not carry some extra information. (a negative example is included in the paper)

In the example, we use the Abilene topology. The idea of SafeGuard is to let packet carry its path cost towards the destination. Suppose the link between Denver and Kansas City fails, and the network is converging. At this moment, a packet is sent from Denver to Kansas City. In current routing, if Denver has updated its states according to the failure, while Sunnyvale has not, the packet will be bounced back and forth between Denver and Sunnyvale, shaping a forwarding loop. If SafeGuard is in use, the packet carries cost 3161 when it leaves Denver, as the path Sunnyvale-Los Angeles-Houston-Kansas City has cost 3161. When Sunnyvale receives the packet, it detects that the packet's cost (3161) is higher than its own cost (1934, through Denver). Thus it can infer that Denver knows a failure for which it has not received the notification. If Denver pre-computes a protection path Sunnyvale-Los Angeles-Houston-Kansas City, it can look it up by using the packet's cost 3161, and forward through it. Eventually the packet can still reach its destination, even though routers on its path have inconsistent states.

• Ang Li, Xiaowei Yang, and David Wetherall, SafeGuard: Safe Forwarding during Route Changes, in ACM CoNEXT, 2008. PDF
• Ang Li, Xiaowei Yang, and David Wetherall, Towards Disruption-Free Intra-Domain Routing, in ACM SIGCOMM Student Poster, 2008. PDF PPT

• Xiaowei Yang
• Ang Li
• David Wetherall

angl AT cs dt duke dt edu