The 31s Annual IEEE Inernaional Conference on Compuer Communicaions: Mini-Conference A Fresh Look a Iner-Domain Roue Aggregaion João Luís Sobrinho Insiuo de Telecomunicações Insiuo Superior Técnico joao.sobrinho@lx.i.p Franck Le IBM T. J. Wason Research fle@us.ibm.com Absrac We presen hree roue aggregaion sraegies o scale he Inerne s iner-domain rouing sysem. These sraegies resul from a keen undersanding on how he cusomer-provider, peer-peer rouing policies propagae roues belonging o long prefixes in relaion o how hey propagae roues belonging o shorer prefixes ha cover he long ones. The firs sraegy, Coordinaed Roue Suppression, requires coordinaion beween he Auonomous Sysems (ASs) of he Inerne, and we presen a proocol o perform such coordinaion. The second sraegy, No Impor Provider Roues, does no require any coordinaion beween he ASs, bu benefis only some of hem. The hird sraegy, Implici Long Roues, does no rely on any coordinaion beween he ASs eiher and i is he mos efficien sraegy. However, i presupposes modificaions o he way rouers build heir forwarding ables. We evaluae he hree roue aggregaion sraegies over a publicly available descripion of he Inerne opology and on synheically generaed Inerne-like opologies. The resuls are very promising, wih savings in he amoun of sae informaion required o susain iner-domain close o he opimum possible. I. INTRODUCTION The Inerne rouing sysem is in need o scale as is growh and is operaional pracices such as he allocaion of provider-independen prefixes, muli-homing, and raffic engineering creae an excessive number of prefixes o be exchanged among, sored by, and accessed a is core rouers [1]. If he problem is already imperious wih IPv4, i can be furher aggravaed wih IPv6, given he added possibiliies for segmenaion of is larger space [2]. Roue aggregaion purpors o subsiue ses of roues peraining o long prefixes by single roues peraining o shorer prefixes ha cover he long prefixes. We make use of roue aggregaion o scale iner-domain rouing, whereby rouing decisions depend on he cusomer-provider and peer-peer agreemens ha Auonomous Sysems (ASs) esablish beween hem [3], [4]. We consider a shor, paren prefix covering each of a number of long, child prefixes in order o presen hree iner-domain roue aggregaion sraegies: Coordinaed Roue Suppression; No Impor Provider Roues; and Implici Long Roues. In all hree sraegies here is an aggregaion node ha generaes a paren roue. The aggregaion node can be any node whose eleced child roues are all cusomer roues. The Coordinaed Roue Suppression aggregaion sraegy builds on he observaion ha if he forwarding-able enry peraining o a given child prefix coincides wih he forwarding-able enry peraining o he paren prefix, hen he former is no needed o expedie daa packes [6]. To ransform his observaion, which is local o a node, o a nework-wide roue aggregaion sraegy requires a minimum of coordinaion beween neighbor nodes. The No Impor Provider Roues aggregaion sraegy resuls from he observaion ha, under cerain mild condiions on he opology of he nework, a node wih an eleced child roue learned from providers may delee ha roue and rely, insead, on he paren roue. This roue aggregaion sraegy does no require any coordinaion beween nodes, bu does no apply o all of hem. The Implici Long Roues aggregaion sraegy is kindled by he suble observaion ha whenever a node expors o a neighbor a paren roue, wihou roue aggregaion i would also expor o ha same neighbor all child roues. Thus, child roues are implici in he exporaion of he paren roue: heir explici exporaion is unnecessary. This sraegy does no require coordinaion among nodes, bu presupposes ha hey are able o consruc heir forwarding ables from implici knowledge. All hree roue aggregaion sraegies are nework-wide, decenralized, and preserve he communicaion pahs impared by he cusomer-provider, peerpeer rouing policies [5]. We evaluae hese hree roue aggregaion sraegies over an inferred opology of he Inerne made publicly available by he Cooperaive Associaion for Inerne Daa Analysis (CAIDA) [7] and over Inerne-like opologies generaed wih a model similar o he one presened in [8]. The resuls show very significan savings in he amoun of sae informaion required o susain iner-domain rouing. The remainder of he paper is organized as follows. Secion II reviews imporan facs abou iner-domain rouing. The hree roue aggregaion sraegies are discussed in Secion III. Secion IV presens experimenal resuls. Secion V debaes relaed work while Secion VI concludes he paper and poins o fuure research. II. INTER-DOMAIN ROUTING The AS-level srucure of he Inerne can be modeled as graph, where each node sands for an AS and each link joins wo ASs wih direc conneciviy beween hem, regulaed eiher by a cusomer-provider agreemen or a peerpeer agreemen [3], [4]. Prefixes are allocaed o ASs. An AS holding a prefix generaes a roue peraining o ha prefix ha is subsequenly propagaed hroughou he whole Inerne by he Border Gaeway Proocol (BGP), in compliance wih he cusomer-provider, peer-peer rouing policies [5]. These policies prescribe he following: a cusomer roue (learned 978-1-4673-0775-8/12/$31.00 2012 IEEE 2556
u 7 p 1 p 2 u 1 2 u 2 1 Fig. 1. Solid double arrows join a provider and a cusomer, wih he provider above he cusomer; dashed double arrows join wo peers. Prefix p is a paren prefix wih child prefixes p 1 and p 2. Node i generaes a p i -roue (i = 1, 2). Node is he aggregaion node: i generaes a p-roue. from a cusomer) is preferred o a peer roue (learned from a peer) which, in urn, is preferred o a provider roue (learned from a provider); an AS expors cusomer roues o all is neighbors, and expors all roues o is cusomers, hese being he only exporaions allowed; all expored roues are impored a he receiving AS. We do no consider oher aribues of BGP relaed o rouing such as AS-PATH and MED. Some erminology will prove useful. Roues peraining o prefix q are called q-roues. Suppose ha node z generaes a q-roue. Afer propagaion by he rouing proocol, each node u z eiher receives a q-roue or does no. If u receives a q-roue, hen is eleced (mos preferred) q-roue can be a cusomer, a peer, or a provider roue. In all hree cases, node u insalls an enry in is forwarding able, poining prefix q o he se f(u; q) of is neighbors from which he eleced q-roue was learned. Such neighbors are called he q-forwarding-neighbors of u. If u does no receive any q-roue, hen is forwarding able does no conain an enry peraining o q. Figure 1 depics a small Inerne-like nework, where a solid double arrow joins a provider and a cusomer, wih he provider a a higher level han he cusomer, and a dashed double arrow joins wo peers. Node 1 generaes a p 1 -roue. The eleced p 1 -roue a node u 7 is a cusomer roue. I is learned from boh and which become he p 1 -forwardingneighbors of u 7, f(u 7 ; p 1 ) = {, }, as shown in each of he sub-figures of Figure 2. (The differences beween he hree sub-figures relae o differen roue aggregaion sraegies o be discussed in he nex secions). We say ha a nework is policy-conneced if a q-roue generaed a any specific node resuls in an eleced q-roue a every node. The nework of Figure 2 is policy-conneced. Hopefully, he Inerne is policy-conneced as well. p u 8 III. ROUTE AGGREGATION A. Aggregaion Node and Aggregaion Coefficien We focus on a shor, paren prefix p conaining each of a collecion of longer, child prefixes p 1, p 2,..., p N. The ses of addresses represened by he child prefixes are pairwise disjoin, hey are conained in he larger se of addresses represened by he paren prefix, alhough hey need no form a pariion of he laer se. The node ha generaes a p i - roue is denoed by i. Given he paren prefix p and is child prefixes p i (1 i N), he goal of roue aggregaion is o scale he rouing processes by judiciously replacing roues and forwarding-able enries peraining o subses of child prefixes by single roues and single forwarding-able enries peraining o he paren prefix, all he while respecing he communicaion pahs ha resul from he cusomer-provider, peer-peer rouing policies. An aggregaion node, denoed by, is chosen o generae a p-roue, which roue is propagaed hroughou he nework by he rouing proocol, as any oher roue. The only consrain ha we impose on he aggregaion node is ha is eleced p i -roue be a cusomer roue for all 1 i N. For provider-dependen prefixes, he choice of aggregaion node is a naural one. For provider-independen prefixes, he choice of aggregaion node may be performed off-line or decided auonomously a a node as long as i saisfies he consrain enunciaed above. We leave a full sudy abou he choice of aggregaion node, paren prefix, and se of child prefixes for anoher work. Regardless of he prefix hey perain o, we say ha a cusomer roue is beer han eiher a peer or a provider roue, and ha a peer roue is beer han a provider roue. Thus, for example, a cusomer paren roue is beer han a provider child roue. The cornersone of our roue aggregaion sraegies, presened in Secions III-B, III-C, and III-D, is he following heorem which esablishes a relaionship beween he eleced p i -roues and he p i -forwarding-neighbors wihou roue aggregaion, on he one hand, and he eleced p-roues and p-forwarding-neighbors, on he oher. Theorem 1. For every node u oher han he aggregaion node : he eleced p i -roue is eiher beer han or as good as he eleced p-roue; if he eleced p i -roue is as good as he eleced p-roue, hen every p-forwarding-neighbor is a p i -forwardingneighbor oo, ha is, f(u; p) f(u; p i ). Our roue aggregaion sraegies are nework-wide, scaling forwarding ables, rouing ables, and he rae of roue exchanges. We measure he efficiency of a roue aggregaion sraegy by he normalized difference beween he oal number of eleced roues wihou and wih roue aggregaion. Le m i denoe he number of nodes ha elec a p i -roue wih roue aggregaion, and m denoe he oal number of nodes. Assuming he nework o be policy-conneced, he raio above is expressed by Nm N i=1 (1 + m i), Nm and is called aggregaion coefficien. B. Coordinaed Roue Suppression The following observaion kindles he roue aggregaion sraegy of his secion. If, a a node u, he p i -forwardingneighbors wihou roue-aggregaion coincide wih he p- forwarding-neighbors, hen u does no need a forwardingable enry peraining o child prefix p i [6]. Wihou ha 2557
forwarding-able enry, daa packes wih address conained in p i are expedied across he p-forwarding-neighbors, he same neighbors as wihou roue aggregaion. However, some oher neighbor of u may depend on i o learn a p i -roue and build is own forwarding able. Take Figure 1 as example. The only p 1 -forwarding-neighbor of is which is also is only p- forwarding-neighbor. Node does no need o impor a p 1 - roue from o build is forwarding able. Bu is a p 1 - forwarding-neighbor of u 7 and he p 1 -forwarding-neighbors of u 7, f(u 7 ; p 1 ) = {, }, do no coincide wih is p- forwarding-neighbors, f(u 7 ; p) = { }. Since u 7 learns a p 1 - roue from, needs o impor a p 1 -roue from afer all in order o expor i furher o u 7. Wih a minimum of local coordinaion, nodes can noify heir neighbors when hey do no need o learn a p i -roue from hem. Tha coordinaion is realized wih p i -suppression messages, messages ha a node sends o anoher o ell i ha i does no need o receive a p i -roue. Node u mainains a variable S u conaining he se of is neighbors ha need o learn a p i -roue from i. The nodes of S u are hose o which u has expored a p i -roue and from which i has no received a p i -suppression message. When u expors a p i -roue o is neighbor x i adds x o S u. If, laer on, u receives a p i - suppression message from x, hen i wihdraws x from S u. When u receives a p i -roue from a neighbor v ha does no become a p i -forwarding-neighbor, i sops imporing ha roue and raher replies o v wih a p i -suppression message, meaning ha u does no need o learn a p i -roue from v. Se S u is empy when no neighbor of u relies on i o learn a p i -roue. If S u is empy and he p i -forwarding-neighbors of u coincide wih is p-forwarding-neighbors, hen u does no need o elec a p i -roue. I sops imporing p i -roues alogeher and sends p i - suppression messages o each of is p i -forwarding-neighbors. Le us see he effec of his roue aggregaion sraegy on he nework of Figure 1 (see also Sub-figure 2a). We focus on child prefix p 1. Node 2 has no neighbors o expor a p 1 -roue o. I can reach boh 1 and via eiher one of is providers and, f( 2 ; p 1 ) = {, } = f( 2 ; p). Thus, 2 does no impor p 1 -roues. I sends p 1 -suppression messages o and. Likewise, u 2 does no impor p 1 -roues and sends a p 1 - suppression message o. Nodes 2 and u 2 were he only nodes o which node expored a p 1 -roue. Since received p 1 -suppression messages from boh hese nodes, se S u4 becomes empy, and since reaches boh and 1 exclusively hrough, f(, p 1 ) = { } = f( ; p), i sops imporing he p 1 -roue learned from and sends i a p 1 -suppression message. Node u 8 expors a p 1 -roue o boh u 7 and, bu does no become a p 1 -forwarding-neighbor of eiher of hese nodes. They boh send i a p 1 -suppression message. Therefore, S u8 becomes empy. Because u 8 reaches boh and 1 exclusively hrough, f(u 8 ; p 1 ) = { } = f(u 8 ; p), i sops imporing he p 1 -roue learned from and sends i a p 1 -suppression message. Node also receives a p 1 - suppression message from. Having received p 1 -suppression messages from all is neighbors, node sees se S u6 become empy. Because reaches boh and 1 exclusively hrough, f( ; p 1 ) = {} = f( ; p), i will sop imporing he p 1 - roue learned from and sends a p 1 -suppression message o he laer node (which is of no consequence here). The colored nodes of Sub-figure 2a are hose ha elec a p 1 -roue. C. No Impor Provider Roues The following consequence of policy-connecedness riggers he roue aggregaion sraegy of his secion. Theorem 2. Suppose ha he nework is policy-conneced. If, wihou roue aggregaion, he eleced p i -roue a a node is a provider roue, hen any of is providers is boh a p i - forwarding-neighbor and a p-forwarding-neighbor. Alhough he hypohesis of policy-connecedness seems a mild one in pracice, i is crucial for he conclusion of Theorem 2 o hold. For example, consider he nework of Figure 1 wihou link u 7. The eleced p 1 -roue a u 1 is a provider roue wih being he sole p 1 -forwarding-neighbor of u 1. On he oher hand, here is no p-roue a u 1. Such a roue would have o be learned from and could only have learned i from 1. However, 1 does no expor o is provider he provider roue learned from. The relevance of Theorem 2 resides in he fac ha, under policy-connecedness, he p i -forwarding-neighbors wihou roue aggregaion and he p-forwarding-neighbors are he same a nodes whose eleced p i -roues are provider roues. Therefore, hese nodes do no need forwarding-able enries peraining o p i. Moreover, if such a node belongs o he se of p i -forwarding-neighbors of any oher node, hen he eleced p i -roue a he laer node is also a provider roue, and can be dispensed wih as far as forwarding of daa packes wih address conained in p i is concerned. These observaions righly sugges ha he pahs raversed by daa packes wih address conained in p i are unchanged wih a roue aggregaion sraegy whereby all nodes whose eleced p i -roues are provider roues sop imporing hem. We call his roue aggregaion sraegy No Impor Provider Roues. In Figure 1, nodes u 1, u 2,, and 2 are exacly he ones ha elec a p 1 -provider roue, as shown in Sub-figure 2b. They can refrain from imporing he p 1 -roues learned from heir providers wihou disoring he flow of daa packes. Especially, node 2 will sill be able o balance daa packes wih address conained in p 1 beween and (muli-homing). The No Impor Provider Roues aggregaion sraegy does no require any kind of coordinaion among he nodes. On he oher hand, i only saves on he forwarding-able sizes of hose nodes whose eleced p i -roues are provider roues. In paricular, here are no savings o he so called Tier- 1 nodes, which are he ones wihou providers. Being an uncoordinaed sraegy, i may happen ha no all nodes abide o he No Impor Provider Roues aggregaion sraegy a he same ime. Ye, nodes have incenives o comply wih he sraegy. Consider he example of Figure 1 in relaion o child prefix p 1 (see also Sub-figure 2b). Node elecs a provider p 1 -roue, ha was learned from. If does no impor ha roue, hen i saves on is forwarding-able 2558
u 7 u 8 u 7 u 8 u 7 u 8 u 1 1 2 u 2 u 1 2 u 2 1 u 1 1 2 u 2 (a) (b) (c) Fig. 2. The p 1 -forwarding-neighbors of he nodes of Figure 1 and hree roue aggregaion sraegies: (a) Coordinaed Roue Suppression; (b) No Impor Provider Roues; (c) Implici Long Roues. Colored nodes are hose ha elec a p 1 -roue. size wihou changing is forwarding of daa packes. Thus, has an incenive o follow No Impor Provider Roues. Assume ha i does so. Then, no longer expors a p 1 - roue o u 2 or o 2. The forwarding of daa packes a u 2 is unperurbed by his absence. Tha is no so in relaion o 2. This node learns a p-roue from and boh a p-roue and a p 1 -roue from. Because of he longes-mach prefix rule, 2 will sar forwarding daa packes wih address conained in p 1 exclusively o, hus forsaking muli-homing. However, node 2 has a double incenive o refrain from imporing he p 1 -roue learned from. I saves on he size of is own forwarding able and i revers o balancing he forwarding of daa packes wih address conained in p 1 across is providers and. D. Implici Long Roues Theorem 1 saes ha he eleced p i -roue a any node (oher han he aggregaion node) wihou roue aggregaion is beer han or as good as he eleced p-roue a he same node. In urn, his conclusion implies ha whenever a node expors a p- roue o a neighbor, wihou roue aggregaion i also expors a p i -roue o ha same neighbor. This remark suggess ha he neighbor can infer he p i -roue from he p-roue wihou explici exporaion of he former, he presence of a p-roue sanding for iself and for he presence of a p i -roue. If a node u learns a p-roue from every neighbor from which i learns a p i -roue, hen u can sop imporing p i -roues. The forwarding-able enry a u peraining o he paren prefix p poins a he same neighbors ha would be poined a by he forwarding-able enry peraining o he child prefix p i, since each learned p-roue implicily represens a p i -roue as well. Now, consider a node u ha does no learn a p-roue from a leas one neighbor from which i learns a p i -roue. In his case, node u has o keep a forwarding-able enry peraining o child prefix p i and has o build his forwardingable enry aking ino accoun he meaning of learned p-roues as sanding for hemselves and for p i -roues. Specifically, if he eleced p i -roue is as good as he eleced p-roue, hen he se of neighbors poined a by he forwarding-able enry peraining o p i mus be compounded wih he p-forwardingneighbors. And, if he eleced p i -roue is worse han he eleced p-roue, hen he se of neighbors poined a by he forwardingable enry peraining o p i mus be replaced by he se of p- forwarding-neighbors. We call his roue aggregaion sraegy Implici Long Roues. Consider again Figure 1 wih respec o child prefix p 1 and assume ha all nodes abide o he Implici Long Roues aggregaion sraegy (see also Sub-figure 2c). I is easy o verify ha each of he nodes 2, u 1, u 2,,,, and u 8 learn p-roues from exacly he same neighbors from which hey learn p 1 -roues. Therefore, each of hese nodes can sop imporing p 1 -roues, and hey may perceive an advanage in doing so since i saves on heir forwarding-able sizes. Because node does no elec a p 1 -roue, i can expor none o u 7. Thus, u 7 learns a p 1 -roue from is cusomer and a p-roue from is cusomer. According o Implici Long Roues, node u 7 builds is forwarding-able enry peraining o p 1 from and from is p-forwarding-neighbors, which is jus. Ulimaely, he forwarding-able enry peraining o p 1 poins a se {, }, he same se as wihou roue aggregaion. Noe ha u 7 has an incenive o build is forwarding able as described since i allows i o spread daa packes wih address conained in p 1 over and. Sub-figure 2c shows which nodes need o elec a p 1 -roue according o he Implici Long Roues aggregaion sraegy. IV. RESULTS We presen a summary of resuls relaed o he performance of he hree roue aggregaion sraegies: Coordinaed Roue Aggregaion (CRA); No Impor Provider Roues (NIPR); and Implici Long Roues (ILR). We have realized he sraegies boh on an inferred AS-level opology of he Inerne provided by CAIDA [7] and on synheic Inerne-like opologies generaed according a model similar o ha presened in [8]. Tier-1 ASs are hose wihou providers. The Tier of any oher AS is one plus he Tier of is provider of highes Tier. Sub ASs are hose wihou cusomers. We randomly (uniform disribuion) seleced an AS o ake he role of aggregaion node and randomly (uniform disribuion) assigned child prefixes o he sub ASs ha can be reached from he aggregaion node hrough a sequence of cusomer ASs. Table I summarizes he resuls for four child prefixes. The aggregaion coefficiens increase wih he Tier of he aggregaion node, since higher- Tier aggregaion nodes correspond o beer clusering of he ASs ha hold he child prefixes. However, even for Tier-1 aggregaion nodes, he aggregaion coefficiens are very close o he opimum value, which is 0.75 for four child prefixes. As expeced from heir descripion, Implici Long Roues yields he highes aggregaion coefficiens, followed by Coor- 2559
TABLE I ROUTE AGGREGATION COEFFICIENTS FOR FOUR CHILD PREFIXES, AS A FUNCTION OF THE TIER OF THE AGGREGATION NODE. 4 Prefixes Inferred Inerne Synheic Topology CRA 0.718 0.727 Tier 1 NIPR 0.715 0.725 ILR 0.719 0.727 CRA 0.731 0.731 Tier 2 NIPR 0.713 0.727 ILR 0.732 0.731 CRA 0.742 0.740 Tier 3 NIPR 0.711 0.730 ILR 0.743 0.740 TABLE II ROUTE AGGREGATION COEFFICIENTS FOR 8 AND 16 CHILD PREFIXES WITH TIER-1 AGGREGATION NODES. Tier 1 Inferred Inerne Synheic Topology CRA 0.842 0.850 8 Prefixes NIPR 0.840 0.848 ILR 0.842 0.850 CRA 0.911 0.916 16 Prefixes NIPR 0.899 0.914 ILR 0.912 0.916 dinaed Roue Aggregaion, wih No Impor Provider Roues remaining for las, alhough he aggregaion coefficiens of he firs wo aggregaion sraegies are barely he same. The resuls presened in able I indicae ha he size of he forwarding ables, and he number of roues o be sored and exchanged in he Inerne can be significanly reduced hrough roue aggregaion. Table II presens aggregaion coefficiens for when he number of child prefixes increases o 8 and o 16. The resuls are close o he opima of 0.875 and 0.938, respecively, furher confirming ha he proposed aggregaion sraegies can significanly scale he Inerne s iner-domain rouing sysem. V. RELATED WORK References [6], [9] propose Forwarding Table Aggregaion. This is a echnique local o each node which consiss in he idenificaion, in is forwarding able, of paren and child prefixes poining a he same se of neighbors. The forwardingable enries peraining o hese child prefixes can be deleed wihou disurbing he flow of daa packes. This approach reduces he size of he forwarding ables, on accoun of heir pos-processing afer he usual updaes ha arise from roues eleced by he rouing proocol, bu i does no scale he rouing processes ha susain he forwarding ables. In conras o [6], [9], our roue aggregaion sraegies do no require any pos-processing of forwarding ables, excep, possibly, a he aggregaion node. More significanly, our roue aggregaion sraegies, especially No Impor Provider Roues and Implici Long Roues, scale he whole rouing processes, no jus he forwarding ables. VI. CONCLUSIONS AND FUTURE WORK We proposed novel roue aggregaion sraegies o scale he Inerne s iner-domain rouing sysem. Given a paren prefix and se of child prefixes, we choose for aggregaion node any one node ha elecs a cusomer roue o reach each of he child prefixes. Coordinaed Roue Suppression is based on he observaion ha if a child prefix s forwarding-neighbors a a node coincide wih he paren prefix s forwarding-neighbors, hen he forwarding-able enry corresponding o he child prefix is no needed. To consruc a roue aggregaion sraegy from his forwarding-plane observaion, some coordinaion is required beween nodes. No Impor Provider Roues is based on he observaion ha if he nework is policy-conneced, hen a node ha elecs a provider roue o reach a child prefix ends up no needing ha roue afer all. I is an uncoordinaed sraegy which nodes have incenives o embrace. The boldes proposal is Implici Long Roues. I is based on he observaion ha if a paren roue is expored from a node o a neighbor, hen a child roue would also be expored from he former o he laer node wihou roue aggregaion. Thus, child roues are implici in paren roues, no needing o be expored explicily. This sraegy is uncoordinaed, provides he highes performance, bu relies on a node s abiliy o build is forwarding able aking implici child roues ino accoun. All hree roue aggregaion sraegies remain faihful o he communicaion pahs he resul from he cusomer-provider, peer-peer agreemens ha govern iner-domain rouing and all yield aggregaion coefficiens ha are close o he opimum. A number of issues remain for furher inquiry. We highligh wo of hem here. Firs, we considered a simple address hierarchy consising of pairs paren-prefix, se-of-child-prefixes. This hierarchy can be exended o a full address ree wih muliple levels of descendans (or ascendans) younger han children (older han parens). Second, we did no address he robusness of he proposed roue aggregaion sraegies o link failures and addiions. I urns ou ha Coordinaed Roue Suppression requires exra coordinaion o deal wih failures and addiions, bu ha No Impor Provider Roues and Implici Long Roues are inherenly robus o failures. ACKNOWLEDGMENTS The work of João Luís Sobrinho was parly suppored by FCT projec PEs-OE/EEI/LA0008/2011. REFERENCES [1] V. Fuller and T. Li, Classless iner-domain rouing (CIDR): The inerne address assignmen and aggregaion plan, Augus 2006, RFC 4632. [2] D. Meyer, L. Zhang, and K. Fall, Repor from he IAB workshop on rouing and addressing, Sepember 2007, RFC 4984. [3] G. Huson, Inerconnecion, peering and selemens - par I, Inerne Proocol Journal, vol. 2, no. 1, pp. 2 16, March 1999. [4], Inerconnecion, peering and selemens - par II, Inerne Proocol Journal, vol. 2, no. 2, pp. 2 23, June 1999. [5] L. Gao and J. Rexford, Sable Inerne rouing wihou global coordinaion, IEEE/ACM Transacions on Neworking, vol. 9, no. 6, pp. 681 692, December 2001. [6] X. Zhao, Y. Liu, L. Wang, and B. Zhang, On he aggregaabiliy of rouer forwarding ables, in Proc. INFOCOM 2010, March 2010, pp. 848 856. [7] The CAIDA AS relaionships daase, January 2010, hp://www.caida.org/daa/acive/as-relaionships/. [8] A. Elmokashfi, A. Kvalbein, and C. Dovrolis, On he scalabiliy of BGP: he role of opology growh, IEEE Journal on Seleced Areas in Communicaions, vol. 28, pp. 1250 1261, Ocober 2010. [9] V. Khare, D. Jen, X. Zhao, Y. Liu, D. Massey, L. Wang, B. Zhang, and L. Zhang, Evoluion owards global rouing scalabiliy, IEEE Journal on Seleced Areas in Communicaions, vol. 28, pp. 1363 1375, Ocober 2010. 2560