Sensibility analysis of BGP
convergence and scalability
using network simulation
Wolfgang Mühlbauer
5. Oktober 2004
SEP: Sensibility analysis of BGP convergence and scalability
using network simulation
Outline
• Running the experiments
• Influence of MRAI timer settings on
– convergence times
– number of updates
• Propagation of updates
– number of affected ASes
– propagation radius
SEP: Sensibility analysis of BGP convergence and scalability
using network simulation
Experiments - SSFNet
• Network simulation with SSFNet
– global view
– existing BGP implementation
• Modifications to SSFNet
– Modeling the behavior of Cisco routers
• Normal distribution of MRAI timer value
• Community values
• Best Path Selection Process, …
– Configuring link failures
– MRAI timer basis: per-peer or per-prefix, …
SEP: Sensibility analysis of BGP convergence and scalability
using network simulation
Experiments – Doing simulation
AS Pairs
Subtree
(AS Pairs)
DML Files
Simulatio
nSSFNet
• AS Pairs: define topology, reflect
commercial relationships (e.g. 12>13)
• Subtree extraction: reduce complexity
and size of sample networks
• DML Files: configuration files, input for
SSFNet
SEP: Sensibility analysis of BGP convergence and scalability
using network simulation
Experiments – DML Files
• Topology Converter: Automatical
generation of DML files out of AS Pairs
• Configurable BGP parameters:
– MRAI timer
– Link failure dynamics
– Interior structure of ASes (route reflectors, …)
– WRATE, SSLD
–…
SEP: Sensibility analysis of BGP convergence and scalability
using network simulation
Experiments – Sample topologies
# ASes
Middle Topology
Topology 1140
Topology 7774
15
95
105
# external
links
27
1145
614
based on AS
Pairs?
no
yes (2003)
yes (04/2004)
Middle Topology
SEP: Sensibility analysis of BGP convergence and scalability
using network simulation
Outline
• Running the experiments
• Influence of MRAI timer settings on
– convergence times
– number of updates
• Propagation of updates
– number of affected Ases
– propagation radius
SEP: Sensibility analysis of BGP convergence and scalability
using network simulation
MRAI – How it works
AS 2
AS 1
AS 5
AS 3
AS 4
SEP: Sensibility analysis of BGP convergence and scalability
using network simulation
MRAI – How it works
AS 2
AS 1
AS 5
AS 3
AS 4
AS 1 issues an update to AS 2 and AS 3
SEP: Sensibility analysis of BGP convergence and scalability
using network simulation
MRAI – How it works
AS 2
AS 1
AS 5
AS 3
AS 4
AS 2 "passes on" the information to AS 4
SEP: Sensibility analysis of BGP convergence and scalability
using network simulation
MRAI – How it works
AS 2
AS 1
AS 5
AS 3
AS 4
timer instance
is started
AS 4 "passes on" the information to AS 5
SEP: Sensibility analysis of BGP convergence and scalability
using network simulation
MRAI – How it works
AS 2
AS 1
AS 5
AS 3
AS 4
AS 3 sends its update to AS 4 not until now!
SEP: Sensibility analysis of BGP convergence and scalability
using network simulation
MRAI – How it works
AS 2
AS 1
?
AS 3
AS 4
AS 5
timer is not
expired yet
AS 4 may prefer to reach AS 1 via AS 3, but …
SEP: Sensibility analysis of BGP convergence and scalability
using network simulation
MRAI – How it works
AS 2
AS 1
AS 5
AS 3
AS 4
timer expires
update is sent, now AS 4 can reach AS 1 via AS 3
SEP: Sensibility analysis of BGP convergence and scalability
using network simulation
MRAI – Simulations
• Automatical testing of 3 dimensions:
different link
failures (5)
MRAI timer
values in sec
(4,5,10,...,60)
different
seeds (20)
• For Topology 7774 measure:
– Convergence time
– Number of external updates
SEP: Sensibility analysis of BGP convergence and scalability
using network simulation
simulation
MRAI – Results
SEP: Sensibility analysis of BGP convergence and scalability
using network simulation
MRAI – per prefix or per peer
per peer
per prefix
0.0.0.1/2
6
0.0.0.2/26
SEP: Sensibility analysis of BGP convergence and scalability
using network simulation
MRAI – per prefix or per peer
• used topologies:
– Topology 1140
– Topology 7774
• testing of 4 dimensions
–
–
–
–
5 different failure scenarios
different MRAI timer values (4s, 5s, 10s, …, 60s)
per-peer and per-prefix timer basis
3 different seeds for random number generator
• we measure
– convergence times
– number of external updates
SEP: Sensibility analysis of BGP convergence and scalability
using network simulation
MRAI – per-prefix vs per-peer
SEP: Sensibility analysis of BGP convergence and scalability
using network simulation
Outline
• Running the experiments
• Influence of MRAI timer settings on
– convergence times
– number of updates
• Propagation of updates
– number of affected Ases
– propagation radius
SEP: Sensibility analysis of BGP convergence and scalability
using network simulation
Propagation – Update Radius
radius 0
radius 0
SEP: Sensibility analysis of BGP convergence and scalability
using network simulation
Propagation – Update Radius
radius 1
radius 1
radius 1
radius 1
radius 1
SEP: Sensibility analysis of BGP convergence and scalability
using network simulation
Propagation – Update Radius
radius 2
radius 2
SEP: Sensibility analysis of BGP convergence and scalability
using network simulation
Propagation – Affected ASes
1) US to D
2) D to US
US providers use link 1 for German destinations
German providers use link 2 for US destinations
SEP: Sensibility analysis of BGP convergence and scalability
using network simulation
Propagation – Affected ASes
1) US to D
2) D to US
Link 1 fails due to some reason
SEP: Sensibility analysis of BGP convergence and scalability
using network simulation
Propagation – Affected ASes
2) D to US
US to D
Even traffic from US to D is now routed over link 2
But: Routers in D won‘t get an update message
and are therefore not „affected“
SEP: Sensibility analysis of BGP convergence and scalability
using network simulation
Propagation – Link Classification
• classify ASes according to their
commercial relationships:
– tier1 ASes: no provider
– stub ASes: no customer
– middle Ases: all the rest
• classify external links according to the
ASes they connect:
tier1-tier1, tier1-middle, middle-middle,
middle-stub, stub-stub
• Harmfulness of links reflected?
SEP: Sensibility analysis of BGP convergence and scalability
using network simulation
Propagation - Simulations
• used topologies:
– Topology Middle
– Topology 1140
– Topology 7774
• testing of 3 dimensions
– 10 different failure scenarios
– different link categories
– 3 different seeds for random number generator
• we measure
– number and ratio of affected ASes
– mean and maximum of propagation radius
SEP: Sensibility analysis of BGP convergence and scalability
using network simulation
Propagation – Affected ASes
SEP: Sensibility analysis of BGP convergence and scalability
using network simulation
Propagation – Affected ASes
Topology 7774
SEP: Sensibility analysis of BGP convergence and scalability
using network simulation
Propagation - Radius
SEP: Sensibility analysis of BGP convergence and scalability
using network simulation
Danke fürs Zuhören!
Email: muehlbaw@in.tum.de
SEP: Sensibility analysis of BGP convergence and scalability
using network simulation