OSPF and BGP Basic SetupWord文件下载.docx
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OSPF and BGP Basic SetupWord文件下载.docx
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area<
areanumber>
"
OSPFworksthroughbroadcast.Areaislikepartitiontoseperatedifferentbroadcastdomain.
AboveisexamplefromCisco,thereare3areasconnectedthroughArea0.Area0isreservedasbackbone.Thebackbonehastobeatthecenterofallotherareas,i.e.allareashavetobephysicallyconnectedtothebackbone.
ForsmallLANenviroment,oneareaisenough.Forourexample,wewillsetasfollowing:
core_a:
router
ospf
10
network
192.168.1.1
0.0.0.0
area
100
access_a:
192.168.1.2
Toseeifitworksornot,wecantrytoseeiftheyfoundtheirneighbour.
core_a#show
ip
neighbor
Neighbor
ID
Pri
State
Dead
Time
Address
Interface
1
FULL/DR
00:
29
FastEthernet0/0
core_a#
ButcurrentlyitonlyexchangeOSPFroutes.NormallywewantOSPFtoredistributeconnectedandstaticroutesforus.Soweneedtoadd:
redistribute
connected
metric-type
subnets
static
Nowletmeaddastaticrouteataccess_a,wecanseeatcore_a
access_a(config)#ip
route
1.1.1.1
255.255.255.255
null0
route
Codes:
C
-
connected,
S
static,
R
RIP,
M
mobile,
B
BGP
D
EIGRP,
EX
EIGRP
external,
O
OSPF,
IA
OSPF
inter
area
N1
NSSA
external
type
1,
N2
2
E1
E2
i
IS-IS,
su
IS-IS
summary,
L1
level-1,
L2
level-2
ia
area,
*
candidate
default,
U
per-user
o
ODR,
P
periodic
downloaded
Gateway
of
last
resort
is
not
set
1.0.0.0/32
subnetted,
[110/21]
via
192.168.1.2,
00,
192.168.1.0/24
directly
DefaultRoute
Bydefault,itwillnotredistributeanydefaultroute.Inordertoletitredistribute,weneedtouse"
default-informationoriginate"
command.
!
default-information
originate
metric
3
1
Now
access_a
learn
the
default
route:
access_a#show
to
0.0.0.0
Null0
O*E1
0.0.0.0/0
110/11
192.168.1.1,
07,
access_a#
Security
AsOSPFwilllearnpeersthemselves,itisbettertoaddauthenticationkeyforsecuritypurpose.
interface
XXXX
message-digest-key
<
keyid>
md5
key>
XX
area-id>
authentication
message-digest
Example:
10
7
096B6B273C363E21
100
CostControl
OSPFcalculatethecostbyinterfacebandwidth.Defaultis(100M/interfacebandwidth).Sothecostwillincreaseby1iftheconnectionisoverFastEthernetinterface,whilethecostwillincreaseby64iftheconnectionisoveraT1link.Thecostaccumulateuntilitreachthedestination.
Intheaboveexample,thecostforAtoreachEwillbe(1+10)=11or(1+1+2)=4.OSPFwillthenchoosethepaththroughCandDwhichhaslowercost.
TherearetwobasicwaytocontrolOSPFcost:
∙Use"
ipospfcostxx"
underinterface.NotethisonlyaffectOSPFroutereceived.
1.1.1.1
Routing
entry
for
1.1.1.1/32
Known
10"
distance
110,
21,
extern
Last
update
from
on
FastEthernet0/0,
05:
10:
43
ago
Descriptor
Blocks:
ago,
Route
traffic
share
count
Metric
=
(redistribution
cost
20)
+
(100M/100M)
21
If
we
apply
under
30,
03
Interface
forced
10.
Total
30.
metric"
parameterduringtheredistribution
Continue
above
example:
09
Change
redistribution
at
to:
50
60,
02
now
become
50)
60
AdvanceControl
Route-maporaccess-listcanbeusetocontrolroutereceive/redistribution.
distribute-list
access-list>
in/out>
subnets
route-map
name>
rf--OSPF-REDISTRIBUTE-CONNECTED
rf--OSPF-REDISTRIBUTE-STATIC
BGP
BGP(BorderGatewayProtocol)isroutingprotocolwidelyusebetweenISPs.UnlikeOSPF,itispeertopeerbasedinsteadofbroadcast.
BGPCaseStudies
BGP:
ConfiguringBGP
PathSelection
BGPuseAS(AutonomousSystems)numberstoindicatethepathtodestination.Eachparty(e.g.ISP)hastheirownASnumber.ASnumber,likeIPaddress,needtoapplyfromrelatedNIC(e.g.APNIC,CNNIC,TWNIC).AlsolikeprivateIPaddress,therearearangeofASnumberreservedforprivateuse.IANAhasreservedAS64512throughtoAS65535tobeusedasprivateASnumbers.
Whenannoucing/redistributingroutestotheirpeers,theirASnumberisprependtotheroutes.Themoretheroutesredistributeamongdifferentparties,thelongertheASpath.
Intheaboveexample,therearetwopathsforAS100tonetworkbroadcastfromAS300:
∙ASpath:
200300
400500300
TherouterwillchoosetheshorterASpathasbestroute.
core_b,f0/0:
192.168.2.1/24
access_b,f0/0:
192.168.2.2/24
core_a,s1/0:
10.10.10.1/30
core_b,s1/0:
10.10.10.2/30
core_a&
access_a,core_b&
access_bhasOSPFrunning
BGPusespeertopeersetupandonerouteronlyuseoneASnumber.Hereistheminimumconfiguration:
bgp
AS
number>
neighbor
remote
peer
IP>
remote-as
xx.xx.xx.xx
mask
yy.yy.yy.yy
Usuallyweuse"
networkxx.xx.xx.xx"
commandtoannouceourIPrangetoremotepeer,insteadofredistributeconnected/static/OSPFroutes.AlsowhenworkingwithISP,theminimumIPsegmentisClassC(/24).
Assume
have
two
ISP
A
and
B,
which
has
AS100
AS200
respectively.
(Use
private
when
working
client
CPE
if
they
don'
t
their
own
AS)
10.10.10.2
200
192.168.1.0
255.255.255.0
core_b:
10.10.10.1
192.168.2.0
Inthisexample,core_aisusingAS100andcore_bisusingAS200.WeannouncethecorrespondingLANIPtoremotenetwork.
summary
BGP
identifier
local
number
table
version
3,
main
routing
3
2
entries
using
234
bytes
memory
path
104
3/2
path/bestpath
attribute
372
AS-PATH
24
0
cache
filter-lis
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