This is used to minimize ibgp peering. It is represented
with parenthesis in the bgp table
RULES:
Ø
Intra confederation means confederation within a
single AS
Ø
Intra confederation AS can be confed internal or confed external
Ø
Select normal ebgp routes over confed ebgp
routes. Select confed ebgp routes over ibgp routes
Ø
A router
that does not support confed cannot operate in a bgp ntwk
Default config
We av decided not to
advertise 20.20.20.0 and 40.40.40.0 into ospf. Instead we wld use next-hop-self
so that addresses can be inserted into bgp table (since rule says next hop
address must be reachable before ntwks can be advertised into bgp)
R1......................
int s0/1
ip add 20.20.20.1 255.255.255.0
no shut
int s0/0
ip add 10.10.10.1 255.255.255.0
no shut
int lo 1
ip add 150.150.150.1 255.255.255.0
no shut
exit
router ospf 1
network 10.10.10.0 0.0.0.255 area 0
exit
R2..................
int s0/0
ip add 10.10.10.2 255.255.255.0
no shut
int s0/1
ip add 30.30.30.2 255.255.255.0
no shut
int lo 1
ip add 77.77.77.1 255.255.255.0
no shut
exit
router ospf 1
network 10.10.10.0 0.0.0.255 area 0
network 30.30.30.0 0.0.0.255 area 0
exit
R3..........................
int s0/1
ip add 40.40.40.1 255.255.255.0
no shut
int s0/0
ip add 30.30.30.1 255.255.255.0
no shut
int lo 1
ip add 99.99.99.1 255.255.255.0
no shut
exit
router ospf 1
network 30.30.30.0 0.0.0.255 area 0
exit
ISP1..................................
int s0/0
ip add 40.40.40.2 255.255.255.0
no shut
int lo 1
ip add 200.200.200.1 255.255.255.0
no shut
exit
router bgp 111
nei 40.40.40.1 remote-as 100
bgp router-id 200.200.200.1
no synchronization
ISP2..................
int s0/1
ip add 20.20.20.2
255.255.255.0
no shut
int lo 1
ip add 100.100.100.1
255.255.255.0
no shut
exit
router bgp 222
nei 20.20.20.1
remote-as 100
bgp router-id
100.100.100.1
no synchronization
Task 1) cfg
confederation such that r2 and r3 are in 65002. and r1 is in 65001. Advertise
ntwk 200.200.200.0 and ntwk 100.100.100.0 into bgp
R1(config)# router bgp
65001
bgp confederation identifier 100
bgp confederation peers 65002
nei 10.10.10.2
remote-as 65002
nei 20.20.20.2
remote-as 222
R2(config)# router bgp
65002
bgp confederation identifier 100
bgp confederation peers 65001
nei 10.10.10.1
remote-as 65001
nei 30.30.30.1
remote-as 65002
R3(config)# router bgp
65002
bgp confederation identifier 100
bgp confederation peers 65001
nei 40.40.40.2
remote-as 111
nei 30.30.30.2
remote-as 65002
Now lets advertise the 100.100.100.0 and 200.200.200.0
ntwk
ISP1(config-router)# network
200.200.200.0 mask 255.255.255.0
ISP2(config-router)# network
100.100.100.0 mask 255.255.255.0
Note that R2 will forward these
routes to R1 and R3 but recall that these routes would not be in the bgp table
of R1 and R3 if the next hop addres ntwk
(i.e. 20.20.20.0) is not their routing table. they do not actualy need to be
able reach it. eg assuming we cfged ntwk 20.20.20.0 0.0.0.255 area 0, then the
ntwk wil shw up in d bgp table irrespective wheda we can reach 20.20.20.2. SO
FAR 20.20.20.0 nwtk shws up in routin table, den bgp wld insert d ntwk into its
bgp table
R1(config-router)# nei 10.10.10.2 next-hop-self
R3(config-router)# nei 30.30.30.2 next-hop-self
Lets do a sh of the
routes
R1(config-router)# do sh ip bgp 200.200.200.0
BGP routing table entry for 200.200.200.0/24, version 3
Paths: (1 available, best #1, table Default-IP-Routing-Table)
(65002) 111
30.30.30.1 (metric 128) from 10.10.10.2 (77.77.77.1)
Origin IGP, metric 0,
localpref 100, valid, confed-external,
best
where 30.30.30.1 is d next hop, 10.10.10.2 is nei ip add and 77.77.77.1
is the router id of d router that advertised it
R2(config-router)# do sh ip bgp 200.200.200.0
BGP routing table entry for 200.200.200.0/24, version 5
30.30.30.1 from 30.30.30.1 (99.99.99.1)
Origin IGP, metric 0,
localpref 100, valid, confed-internal,
best
ISP1# sh ip bgp
Network Next
Hop Metric LocPrf Weight Path
*> 100.100.100.0/24 40.40.40.1 0 100
222 i
*> 200.200.200.0 0.0.0.0 0 32768
i
We see that ISP1 is not aware that a confederation was cfged
R1(config-router)# do sh ip bgp nei 10.10.10.2
BGP neighbor is 10.10.10.2, remote AS 65002, external link
BGP version 4, remote router ID
77.77.77.1
Neighbor under common administration …….that
is under same AS
R2(config-router)# do sh ip bgp nei 30.30.30.1
BGP neighbor is 30.30.30.1,
remote AS 65002,
internal link
BGP version 4, remote router ID
99.99.99.1
Neighbor under common administration
No comments:
Post a Comment