Valley-free violation in Internet routing — Analysis based on BGP Community data

Abstract

The valley-free rule defines patterns of routing paths that allow the Internet Autonomous Systems (AS) to minimize their routing costs through selective announcement of BGP routes. The valley-free rule has been widely perceived as a universal property of the Internet BGP routing that is only violated due to transient configuration errors. Analysing the valleyfree violations is important for a better understanding of BGP behaviour and inter-domain routing. This requires knowledge of the business relationships between ASes. The ground-truth data of AS relationships are not publicly available. Previous algorithms have inferred AS relationships based on the assumption that AS paths should be valley-free. Such inference results are biased and can not provide an objective assessment of the valley-free rule. Instead we extract the AS relationships directly from routing polices encoded in the BGP Community attribute. We are able to extract the business relationship of more than 30% of AS links based on BGP data collected from the RouteViews and RIPE RIS repositories in June 2011. We use our inferred AS relationships to analyse the valley-free violations in BGP routing. We reveal that the non valley-free paths are significantly more frequent than previously reported. As many as one fifth of AS paths in IPv6 BGP updates are valley paths. A substantial portion of these valley paths are persistent during the whole month of measurement. These observations strongly indicate that the valley paths are not merely a result of BGP misconfigurations. Instead they are the outcome of complex business relationships and deliberate policies by ASes using distinct unconventional models.

A survey of interdomain routing policies

“…The model supposes the routing policies obey constraints imposed by business relationships between neighboring autonomous systems. While a number of measurement studies have used public data to infer that these constraints are sometimes violated [10,14,32,37], our survey presented a unique opportunity to ask network operators directly about when and how they violate these constraints; responses suggest that violations are the exception, rather than the rule (Section 4.1). These exceptions may arise from incorrect initial assumptions or changes in routing policies over the past decade.…”

“…How accurate are these models? Researchers have highlighted exceptions to modeled routing policies [10,14,32,37], or aspects of interdomain routing that these models omit [35].…”

Improving the discovery of IXP peering links through passive BGP measurements

“…It should be noted that the valley-free rule is not an enforcement rule. It is observed that a small number of routing paths do not follow this rule, either because of policy misconfigurations [20], or due to the complexity of some AS relationships which is not captured by the simple customer/peer/sibling model [21].…”

A survey on the recent efforts of the Internet Standardization Body for securing inter-domain routing

“…However, there are exceptions to valley-free constraints [24,93] as they are not upheld sometimes to accommodate customized economic models due to a complex AS relationship between the ASes. For example, for contingency connectivity, ASes usually have one or more backup links with other ASes.…”