We present the results for
the experiments conducted on the 44 node topology for the BGP-ANYCAST
simulations. The topology has 34 clients and 10 Anycast
server nodes. Of the 10 Anycast servers, 9 are
located in North America and 1 in Europe. All
servers are configured as “global nodes”. Of the 34 clients, 22 are located
in North America and rest in Europe and Asia.
Normally, we would see clients exhibiting regional affinity – i.e., clients in
North America would be served by servers in North America
and so on. However, due the limited number of ASes
considered in the current topology, we find that clients in North America
(especially the ones located in Western and Central parts of North America) are
serviced by the Anycast server in Europe.
The converse also happens to be true – clients in Russia
were observed to be serviced by servers in North America.
We divided the simulations into 3
categories : One with no failures ; One with link down
failures ; and one with prefix withdrawals. In these initial set of
experiments, we created single failures and created them around the Europe Anycast server, as that
server received maximum number of requests. For the explicit withdraw case we
saw a very quick convergence, as the graph is quite strongly connected (the 44
nodes are connected with 467 links, which is around the halfway mark to being
fully connected). For the link down case, we brought just one of the links that
the AS shares with another AS (which seemed to on the preferred path) was
brought down. However, as the simulation is randomized w.r.t.
starting time of BGP nodes, different best paths were selected in each run of
the simulation and hence, we did not see downtime in all cases.
Each simulation experiment was run for a total of 2000 seconds. For the withdraw case, the prefix was withdrawn at 800th second of the simulation and not re-advertised after that. For the linkdown case, the link was brought down at the 677th fo the simulation. (The times for the failure were chosen quite randomly.) For each case, the simulation was
repeated 50 times. We measured mean response times, % of requests received by Anycast servers etc., as discussed further.
Mean Number of responses received from each Anycast server:
The following graph shows the
mean number of requests received by (or responses received from) each of the Anycast
servers. We see that for the explicit withdraw case, the requests are
distributed to other nodes after the failure. The same does not strongly hold
for the linkdown case.
Percentage of responses
The following graph shows the percentage of responses
received from the Anycast servers. The distribution is
quite similar to the Mean response graph above.
The following graph shows the geographic distribution of the
responses from servers. The graph shows mean responses received by clients from the Anycast
servers in a region.
The linkdown case does not show
much change from the No Failure case, as only one link was down and the clients
could still reach the server through other links.
We measured the flips that the clients observed during the
failure cases. However, since we started clients when the network was in a
steady state and also, since only one failure was simulated, affected clients showed
only one flip. We expect to have interesting results for this case when more
failures are simulated.
The main points of focus for the future are:
modeling multiple network failures. A few studies have shown that few
paths in the internet tend to be prone to frequent failures ( the 80-20 rule applies : 80% of the failures occur in
20% of the links). We plan to simulate such failures and in addition to
reported measurements, we would like to measure flips observed by clients,
network churn ( in terms of number of bgp updates sent etc.)
for hierarchy. Support both global and local nodes and observe the amount
of traffic that is absorbed by the local nodes in failure and no-failure
to a larger network. The current topology is quite strongly connected and
is not quite representative of the Internet. We plan to include tier-2 and
tier-3 service providers in the topology for a richer, realistic topology.