CBGP - SourceForgec-bgp.sourceforge.net/downloads/cbgp-1.pdfOutcome of BGP decision process does not rely on time

Interdomain Routing with BGP4, 2526 Nov. 2004© 2004, B. Quoitin 1.1

Interdomain routing with BGP4Interdomain routing with BGP4

CBGPA new approach to BGP simulation

http://cbgp.info.ucl.ac.be/(1/2)

Bruno Quoitin([email protected])

Université Catholique de LouvainComputer Science and Engineering Dept.


Day 1Day 1

Introduction & Internals


AgendaAgenda

IntroductionHow does it work ? Internals

topology representationsimulator's principleBGP details

How do we use it ? Scriptingsetting up the topologysetting up BGP routerspolicies

Hands on...


MotivationsMotivations

Main interests: Traffic Engineeringstudy effects of manipulating BGP attributesinvestigate changes in BGP protocol

RequirementsPolicy Routing (no protocol dynamics)Large timescale aspects (10ths of minutes,hours)Scalability & efficiency: topologies with same order of magnitude as Internet


MotivationsMotivations

Why a new simulator ?

Traditional simulators do not scaleJavasim/SSFNetPacketlevel simulationGranularity is too high


HistoryHistory

Development started in December 2002under the ATRIUM project and now continued under the TOTEM project.

First version (1.0.0)simplified BGP decision process (localpref, aspath, tiebreak)ASlevel: one router per AS


HistoryHistory

Latest version (1.1.17)complete decision processroute reflectorsversatile filtersintradomain routingvarious MED behaviourscommandline

Announced version (1.1.18)integration within TOTEM toolboxsupport for XML topologies


New approachNew approach

Assumptions:BGP sessions rely on TCPOutcome of BGP decision process does not rely on time

Consequences:Transmission lines never fail => simulator only preserves BGP messages ordering on each transmission lineDeterministic BGP decision process


How does it work ?How does it work ?

Conceptual view

scheduler[queue of events]

script / CLI

start/stop

setup

setup

setup, read update

read

readtopology DB

[nodes, links, ...]

Router configs DB[peerings, ...]

routers states DB[RIBs, sessions...]


Internals (1)Internals (1)

Topology databaseTopology represented as a graph

node = router, identified by a single IP addressedge = physical link

Graph implementationradixtree contains all nodes: O(1)adjacencies maintained in sorted heaps: O(n)

Edge attributesdelay (informal)metric (for intradomain routing)

Current limitation:single link between nodes



Example: topological view

10.0.0.1

10.0.0.2

10.0.0.3

10.0.0.4

physical link

iBGP session

AS110

5

5

5



Example: content of topology database

10.0.0.1 10.0.0.2 10.0.0.3 10.0.0.4

adjacencies(sorted heap)10.0.0.2, 1010.0.0.3, 5

... ... ...

network (radix-tree)



Routers configs databaseList of BGP neighbors (sorted heap)Per peer input/output filters

Routers states databaseRouting table (radixtrees)

STATIC routesIGP routes (computed)BGP routes (filled by BGP decision process)

BGP sessionsAdjRIBs, LocRIBs (radixtrees)



Example: routers configs/states databases

10.0.0.1 10.0.0.2 10.0.0.3 10.0.0.4

BGP neighbors: (sorted heap) 10.0.0.2 [filters, Adj-RIB-in, Adj-RIB-out] 10.0.0.3 [...] 10.0.0.4 [...]

...

...

...

...

...

...

network

Loc-RIB (radix-tree)

Routing table (radix-tree)

.........



SchedulerSingle linear global queueHolds messages (with src, dst and nexthop)Sequential processing of messages by a single threadMessages are propagated hopbyhop until they reach their final destination



Simulator's FIFO queue

PUSHnew msg POP msg

UPDATE [192.168.0/24]src=10.0.0.1dst=10.0.0.2next-hop=10.0.0.2

UPDATE [192.168.1/24]src=10.0.0.3dst=10.0.0.4next-hop=10.0.0.4

...

FIFO queue

Deliver msg tonext-hop router

source routersend msg



Structure of a router (simplified)

yes

yes

dst=local?

BGP peer ?

Forwarding:? route

DecisionProcess

no

drop

yes

nodrop

Output filter

no

Input filter

Loc-RIB

poppedmsg

pushmsg

RT

Adj-RIB-in

Adj-RIB-out



Decision process (simplified)

0). ignores routes with unreachable nexthop1). prefer routes with highest LOCALPREF2). prefer routes with shortest ASPATH...i). prefer eBGP routes over iBGP routes...j). prefer routes with nearest IGP nexthop...n). prefer routes with smallest IP address



Per peer filterssequence of rules (predicates, actions)predicates: match prefix, communityactions: localpref, communities, aspath prepending, ...

Input filter:(predicates, actions)(predicates, actions)...

Output filter:(predicates, actions)(predicates, actions)...

Decisionprocess

Adj-RIB-in Adj-RIB-out

Loc-RIB

Input filter:(predicates, actions)(predicates, actions)...

Adj-RIB-in Adj-RIB-out

Output filter:(predicates, actions)(predicates, actions)...

Peer 1

Peer 2

Peer 1

Peer 2



Filtering one route

filter(ROUTE)foreach (rule R=(predicate, actions))

if (R.predicate matches ROUTE)for (i= 0; i < size(R.actions); i++)

if (R.action[i] == ACCEPT)return ACCEPT;

elsif (R.action[i] == DENY) {return DENY;

elseapply(R.action[i], ROUTE);

return ACCEPT;



Example: running simulation

1.1

2.1

3.1

4.1AS1

FIFO queue

<empty>

Loc-RIB:192.168/16, local

AS2

AS3

AS4



Example: running simulation FIFO queue

192.168/16[AS1]src=1.1dst=2.1

192.168/16[AS1]src=1.1dst=3.1


AS1

AS2

AS3

AS41.1

2.1

3.1

4.1




Loc-RIB:192.168/16, [AS1]


192.168/16[AS1]

AS1

AS2

AS3

AS41.1

2.1

3.1

4.1




192.168/16[AS2 AS1]src=2.1dst=3.1


AS1

AS2

AS3

AS41.1

2.1

3.1

4.1

Loc-RIB:192.168/16, [AS1]





Loc-RIB:192.168/16, [AS1]

192.168/16[AS1]

AS1

AS2

AS3

AS41.1

2.1

3.1

4.1

Loc-RIB:192.168/16, [AS1]




192.168/16[AS2 AS1]src=3.1dst=4.1


AS1

AS2

AS3

AS41.1

2.1

3.1

4.1

Loc-RIB:192.168/16, [AS1]

Loc-RIB:192.168/16, [AS1]





192.168/16[AS2 AS1}

Loc-RIB:192.168/16, AS2 AS1

AS1

AS2

AS3

AS41.1

2.1

3.1

4.1

Loc-RIB:192.168/16, [AS1]

Loc-RIB:192.168/16, [AS1]


Loc-RIB:192.168/16, [AS2 AS1]




192.168/16[AS4 AS2 AS1]src=4.1dst=3.1

AS1

AS2

AS3

AS41.1

2.1

3.1

4.1

Loc-RIB:192.168/16, [AS1]

Loc-RIB:192.168/16, [AS1]


Loc-RIB:192.168/16, [AS2 AS1]




AS1

AS2

AS3

AS41.1

2.1

3.1

4.1

Loc-RIB:192.168/16, [AS1]

Loc-RIB:192.168/16, [AS1]

192.168/16[AS3 AS1}


Loc-RIB:192.168/16, [AS2 AS1]




AS1

AS2

AS3

AS41.1

2.1

3.1

4.1

Loc-RIB:192.168/16, [AS1]

Loc-RIB:192.168/16, [AS1]

192.168/16[AS4 AS2 AS1}

<empty>


Scripting (1)Scripting (1)

How do we setup a CBGP simulation ?through scriptingfile / interactiveCISCOlike syntax

A few main steps:create nodes and linksconfigure static routesconfigure IGPsetup BGP routers (peerings, filters, etc)run simulation...



CISCOlike syntaxsequence of keywords and parameters

cbgp> net add node 10.0.0.1cbgp> bgp add router 1 10.0.0.1cbgp> bgp router 10.0.0.1cbgp-router> add network 192.168/16cbgp-router> add peer 1 10.0.0.2cbgp-router> peer 10.0.0.2 upcbgp-router> exitcbgp> bgp router 10.0.0.1 show rib 192.168/16

Console



Classes of commandsnet ...

commands related to topology and IP routingbgp ...

commands related to BGPsim ...

commands related to the simulatormiscelaneous additional commands


Network commands (1)Network commands (1)

net add node IPaddr

net add link IPaddr1 IPaddr2 Delay

net link IPaddr1 IPaddr2 igpweight Weight

net node IPaddr route add Prefix Nh Metric

net node IPaddr spfprefix Prefix



net node IPaddr show rt Prefix

net node IPaddr1 recordroute IPaddr2

and more...


net add node 10.0.0.1net add node 10.0.0.2net add link 10.0.0.1 10.0.0.2 10


Example

10.0.0.1 10.0.0.210

Routing table: Routing table:

Console


net add node 10.0.0.1net add node 10.0.0.2net add link 10.0.0.1 10.0.0.2 10net node 10.0.0.1 spf-prefix 10/8net node 10.0.0.2 spf-prefix 10/8


Example

10.0.0.1 10.0.0.210

Routing table:10.0.0.2 IGP


Console


net add node 10.0.0.1net add node 10.0.0.2net add node 20.0.0.1net add link 10.0.0.1 10.0.0.2 10net add link 10.0.0.2 20.0.0.1 5net node 10.0.0.1 spf-prefix 10/8net node 10.0.0.2 spf-prefix 10/8net node 10.0.0.2 route add 20.0.0.1/32 20.0.0.1 5net node 20.0.0.1 route add 10.0.0.2/32 10.0.0.2 5

Console


Example

10.0.0.1 10.0.0.210

Routing table:10.0.0.2/32 IGP

Routing table:10.0.0.1/32 IGP20.0.0.1/32 STATIC

Domain 1

Domain 220.0.0.1

Routing table:10.0.0.2/32 STATIC


net options igp-inter onnet add node 10.0.0.1net add node 10.0.0.2net add node 20.0.0.1net add link 10.0.0.1 10.0.0.2 10net add link 10.0.0.2 20.0.0.1 5net node 10.0.0.1 spf-prefix 10/8net node 10.0.0.2 spf-prefix 10/8

Console


Example

10.0.0.1 10.0.0.210

Routing table:10.0.0.2/32 IGP20.0.0.1/32 IGP

Routing table:10.0.0.1/32 IGP20.0.0.1/32 IGP

Domain 1

Domain 220.0.0.1



BGP commands (1)BGP commands (1)

bgp add router ASnum IPaddr

bgp router IPaddr add network Network

bgp router IPaddr1 add peer ASnum IPaddr2

bgp router IPaddr1 peer IPaddr2 up

bgp router IPaddr1 peer IPaddr2 nexthopself



bgp router IPaddr1 show rib IPaddr2|Prefix/*

bgp router IPaddr1 show ribin Peer|* IPaddr2|Prefix|*

bgp router IPaddr recordroute Prefix

bgp router IPaddr1 peer IPaddr2nexthopselfrrclientvirtualrecv Message


bgp add router 1 10.0.0.1bgp router 10.0.0.1

add peer 1 10.0.0.2peer 10.0.0.2 up

bgp add router 1 10.0.0.2bgp router 10.0.0.2

add peer 1 10.0.0.1peer 10.0.0.1 up

sim run


Example (iBGP)

10.0.0.1 10.0.0.210



ConsoleAS1 AS1

iBGP sessionAS 1



Example (eBGP)

10.0.0.1 10.0.0.210


Routing table:10.0.0.1/32 IGP20.0.0.1/32 STATIC20.0.0/24 BGP

AS 1

AS 220.0.0.1

Routing table:10.0.0.2/32 STATIC20.0.0/24 BGP

iBGP

eBGP

bgp router 10.0.0.2add network 10.0.0/24add peer 2 20.0.0.1peer 20.0.0.1 up


sim run

Console

! missing route !(20.0.0/24)



Nexthopself

bgp router 10.0.0.2add network 10.0.0/24add peer 2 20.0.0.1peer 20.0.0.1 next-hop-selfpeer 20.0.0.1 up


sim run

Console

10.0.0.1 10.0.0.210

Routing table:10.0.0.2/32 IGP20.0.0/24 BGP

Routing table:10.0.0.1/32 IGP20.0.0.1/32 STATIC20.0.0/24 BGP

AS 1

AS 220.0.0.1

Routing table:10.0.0.2/32 STATIC20.0.0/24 BGP

iBGP

eBGP

Use peer 20.0.0.1 next-hop-self



without Nexthopself



sim run

Console

10.0.0.1 10.0.0.210

Routing table:10.0.0.2/32 IGP20.0.0.1/32 IGP20.0.0/24 BGP

Routing table:10.0.0.1/32 IGP20.0.0.1/32 IGP20.0.0/24 BGP

20.0.0.1

Routing table:10.0.0.2/32 IGP10.0.0/24 BGP

Use net options igp-inter on

AS 1

AS 2

iBGP

eBGP


Miscellaneous commandsMiscellaneous commands

sim run

include Scriptexample: include /workspace/scripts/toto.cli

print Messageexample: print “Hello World\n”

# This is a comment


Policies (1)Policies (1)

bgp router IPaddr1 peer IPaddr2 filter [in|out]addruleinsertrule Indexremoverule Index

where a rule is composed ofmatch logical combination of predicatesactions comma separated list of actions



Supported match predicatesany

match all routescommunity is Community

match routes that contain given community(specified as X or X:Y)

prefix is Prefixmatch routes for exact given prefix

prefix in Prefixmatch routes contained in given prefix



Not yet implementedregular expressions on ASPathless specific prefixes



Supported actionsaccept

accept the routedeny

deny the routeaspath prepend Amount

prepend the route's aspath Amount timescommunity add Community

add the given community to the routecommunity strip Community

remove all the route's communities



Supported actions (cont')localpref Pref

change the route's localprefmetric Med|internal

change the route's multiexitdiscriminator(absolute value or based on IGP)

redcommunity add prepend Amount Targetadd a redistribution community that requestsprepending Amount times towards Target

redcommunity add ignore Targetadd a redistribution community that requestsignoring Target



ExamplePrefer routes received from neighbor 2.0.0.1

bgp router 1.0.0.1add peer 2 2.0.0.1peer 2.0.0.1

filter inadd-rule

match anyaction “local-pref 120”



ExampleDeny routes towards martian prefix 192.168/16

bgp router 1.0.0.1add peer 2 2.0.0.1peer 2.0.0.1

filter outadd-rule

match “prefix is 192.168/16”action deny


CBGP results (1)CBGP results (1)

Different meansdisplaying routing table of one routerdisplaying AdjRIBin and LocRIB of one BGP routertraceing route from one router to anothertraceing ASpath from one router to a prefixrecording BGP messages exchanged during the simulation



Routing table of one node

cbgp> net node 1.0.0.1 show rt *4.0.0.0/8 4.0.0.1 0 BGP4.0.0.1/32 4.0.0.1 5 STATIC5.0.0.0/8 5.0.0.2 0 BGP5.0.0.2/32 5.0.0.2 5 STATIC

cbgp> net node 1.0.0.1 show rt 5/85.0.0.0/8 5.0.0.2 0 BGP

cbgp> net node 1.0.0.1 show rt 5.0.0.25.0.0.2/32 5.0.0.2 5 STATIC



LocRIB of one router

cbgp> bgp router 1.0.0.1 show rib *i> 1.0.0.0/8 1.0.0.1 0 0 null i*> 4.0.0.0/8 4.0.0.1 0 4294967295 4 i*> 5.0.0.0/8 5.0.0.2 0 4294967295 5 i

cbgp> bgp router 1.0.0.1 show rib 5/8*> 5.0.0.0/8 5.0.0.2 0 4294967295 5 i

cbgp> bgp router 1.0.0.1 show rib 5.0.0.2*> 5.0.0.0/8 5.0.0.2 0 4294967295 5 i



AdjRIBin of one router

cbgp> bgp router 1.0.0.1 show rib-in 4.0.0.1 ** 2.0.0.0/8 4.0.0.1 0 4294967295 4 2 i*> 4.0.0.0/8 4.0.0.1 0 4294967295 4 i* 6.0.0.0/8 4.0.0.1 0 4294967295 4 2 6 i



Traceing route

cbgp> net node 1.0.0.1 record-route 5.0.0.21.0.0.1 5.0.0.2 SUCCESS 1.0.0.1 5.0.0.2

cbgp> net node 1.0.0.1 record-route 6.0.0.21.0.0.1 6.0.0.2 SUCCESS 1.0.0.1 2.0.0.1 6.0.0.1 6.0.0.2



Traceing ASpath

cbgp> bgp router 1.0.0.1 record-route 5/81.0.0.1 5.0.0.0/8 SUCCESS 1 5

cbgp> bgp router 1.0.0.1 record-route 6/81.0.0.1 6.0.0.0/8 SUCCESS 1 2 6



Recording BGP messagesuse “bgp options msgmonitor File”

...6.0.0.2|BGP4|114.00|W|6.0.0.1|6|5.0.0.0/85.0.0.2|BGP4|127.00|A|5.0.0.1|5|6.0.0.0/8|3 6|IGP|5.0.0.1|0||1.0.0.1|BGP4|147.00|A|5.0.0.2|5|6.0.0.0/8|5 3 6|IGP|5.0.0.2|0||5.0.0.1|BGP4|147.00|W|5.0.0.2|5|6.0.0.0/8...


Routereflectors (1)Routereflectors (1)

GoalDecrease number of iBGP sessionsDecrease information known by BGP routersAffect routing choices

How to setup RRs ?Only change sessions with RRclients



Example

client client

RR

AS1

bgp router 1.0.0.1add peer 1 1.0.0.2add peer 1 1.0.0.3peer 1.0.0.2 rr-clientpeer 1.0.0.3 rr-clientpeer 1.0.0.2 uppeer 1.0.0.3 up

Console

Only change sessions with RR-clients

1.0.0.1

1.0.0.31.0.0.2



Multiple RRs

client client

RR

AS1

bgp router 1.0.0.1add peer 1 1.0.0.2add peer 1 1.0.0.3add peer 1 1.0.0.4peer 1.0.0.2 rr-clientpeer 1.0.0.3 rr-clientpeer 1.0.0.2 uppeer 1.0.0.3 uppeer 1.0.0.4 up

Console

1.0.0.1

1.0.0.31.0.0.2

1.0.0.4

RR

Fullmesh of iBGP sessions between RRsDefault clusterID based on IP address (change with set clusterid)


Hands on... (1)Hands on... (1)

Installationdownload from http://cbgp.info.ucl.ac.be/

libgds 1.1.5cbgp 1.1.17

tar xvzf libgds1.1.5.tar.gzcd libgds1.1.5./configure; make; sudo make installcd ..tar xvzf cbgp1.1.17.tar.gzcd cbgp1.1.17./configure; make


Hands on... (2)Hands on... (2)

ExercisesEx1: Write a CBGP script that models basetopo1 (next slide)

Ex2: Based on the topo of Ex1, show the inbound and outbound paths passing on each access link of AS6

Ex3: Try to balance the inbound/outbound paths on each access link of AS6 using localpref and aspath prepending


basetopo1basetopo1

Documents

CBGP - SourceForgec-bgp.sourceforge.net/downloads/cbgp-1.pdfOutcome of BGP decision process does not rely on time