A Study of Global Inter-domain Dynamics using Link Weight Measurements

 

Please contact Mohit Lad (mohit@cs.ucla.edu) or Jong Han Park (jpark@cs.ucla.edu) for any questions or concerns.

2008.01.08

 

We are investigating long-term routing instabilities by analyzing aggregate route changes from multiple BGP monitors for 6 months period of time from Jan 1, 2007 to June 30, 2007. The basic idea is to weigh links using number of routes carried as seen by an observation point and examine how these weights change. The BGP data we used are from 59 monitors and contain more than 22,000 ASes and 60,000 links.  We observe that some links see “significant” route changes repeatedly, and were wondering if anybody either from the ISPs involved or otherwise can throw more light on these.

 

Table 1 shows the top 10 most frequently active links that are observed by most of the monitors during the 6 months time period.

 

LINK

# of times detected as active

174 (Cogent) – 9121 (TTNet)

166

3257 (Tiscali) – 9121 (TTNet)

113

9304 (Hutchison) – 15412 (Flag Telecom)

55

1273 (Cable&Wireless) – 4651 (Thai Gateway)

54

6762 (Seabone) – 7473 (Singapore Telecom)

39

1299 (Telianet) – 4837 (China Backbone)

35

174 (Cogent) – 4648 (Netgate Telecom)

31

3549 (Global Crossing) – 6389 (Bell South)

24

3491 (BTN) – 20485 (TransTelecom)

18

4761 (Indosat) – 5511 (France Telecom)

17

6453 (Teleglobe) – 30890 (Evolva Telecom)

16

Table 1. Top 10 Active Links

 

To give some insight of the kind of weight changes experienced, we present some instances of the routing changes involving the first 5 active links using LinkRank Tool.

Note for all figures below, blue node indicates observation point, the weight (label) on each link indicates the number of routes gained (if positive) or lost (if negative) in that time interval with red indicating loss and green indicating gain. 

 

Link 174 – 9121

 

Figure 1(a) and Figure 1(b) depicts LinkRank graph for this particular link at one of the time intervals in which this link was active.

 

 

                     (a)                                                  (b)

Figure 1. LinkRank graph observed from monitor 129.250.0.171 (a) At 2007-03-08 07:45 GMT, link 174-9121 loses 1128 routes (b) At 2007-03-08 07:50 GMT, link 174-9121 gains 874 routes.

 

Observe that about 1100 routes lost along 2914-9121 sub-path are distributed along many other links (Figure 1a). A short while later, things return back to normal (Figure 1b). This phenomenon persists about 30-40 times per month from March 2007 to June 2007.  From Jan 2007 to Feb 2007, the link does not seem to have this behavior.

 

Figure 2 below depicts another LinkRank graph from another monitor at the same time period.

 

 

               (a)                                    (b)

Figure 2. LinkRank graph observed from monitor 216.18.31.102 (a) At 2007-03-08 07:45 GMT, link 174-9121 loses 1001 routes (b) At 2007-03-08 07:50 GMT, link 174-9121 gains 747 routes.

 

This file lists times that this link appears as active, and you can load file1 and file2 to LinkRank to duplicate the above graphs.

 

Link 3257 – 9121

 

Now we move to the next active link, 3257 – 9121. This particular link sees changes from Jan 2007 to Feb 2007.  The link does not exhibit this behavior from March 2007 to May 2007.  Then in June 2007, the link starts to appear as active again.

 

Figure 3 below shows LinkRank graph of this link in one of the time intervals appeared as active.

 

 

           (a)                       (b)

Figure 3. LinkRank graph observed from monitor 12.0.1.63 (a) At 2007-01-22 00:35 GMT, link 3257-9121 loses 888 routes (b) At 2007-01-22 00:45 GMT, link 3257-9121 gains 889 routes.

 

LinkRank graphs with other monitors show similar observation. Routes are lost and gained within a 10 minute span.

 

This file lists times that this link appears as active, and you can load file1 and file2 to LinkRank to duplicate the above graphs.

 

Link 9304 – 15412

 

Starting from Feb 2007 to June 2007, it appears about 5 to 10 times as active per month.  This link appears as active 15 times on May 19, 2007.  In each active time interval, its LinkRank graph looks similar to the graphs in Figure 4.

 

 

(a)                                          (b)

Figure 4. LinkRank graph observed from monitor 144.228.241.81 (a) At 2007-05-19 04:20 GMT, link 9304-15412 loses 570 routes (b) At 2007-05-19 05:20 GMT, link 9304-15412 gains 568 routes.

 

We suspect that some change took place at the end of Jan 2007 regarding this link and caused this instability.

 

This file lists times that this link appears as active, and you can load this file to LinkRank to duplicate the above graphs.

 

Link 1273 – 4651

 

Unlike any of the above links, this link appears as active uniformly throughout the 6 months period that we study.  Figure 5 shows the LinkRank graphs of this link when active.

 

 

(a)                                                                                                                               (b)

Figure 5. LinkRank graph observed from monitor 134.222.86.174 (a) At 2007-05-27 07:17 GMT, link 1273-4651 loses 1201 routes (b) At 2007-05-27 07:18 GMT, link 1273-4651 gains 1205 routes.

 

This file lists times that this link appears as active, and you can load this file to LinkRank to duplicate the above graphs.

 

 

Link 6762 – 7473

 

This link also appears as active uniformly throughout the 6 months period that we study.  Figure 6 shows the LinkRank graphs of this link when active.

 

 

               (a)                                      (b)

Figure 6. LinkRank graph observed from monitor 157.130.10.233 (a) At 2007-05-02 05:30 GMT, link 6762-7473 gains about 400 routes (b) At 2007-05-02 05:31 GMT, link 6762-7473 loses about 400 routes.

 

This file lists times that this link appears as active, and you can load this file to LinkRank to duplicate the above graphs.