This is used to minimize the no of ibgp peering within our
AS.
RULES:
Ø
We have the route-reflector (which reflects the
routes to the clients) and the Route-reflector Clients
Ø
When a RF gets an update from a non-client, it
forwards it to ebgp peers and clients. When it gets update from a client,it
forwards it to all client peers except the sender. When it gets up date from an ebgp peer, it forwards to all peer.
Ø
Client shld only av ibgp peering with their RF
Ø
Cluster-id and originator id are used to detect
loops in a redundant Rf design
Ø
For ibgp routes, prefer a non-reflected route to
a reflected route. For two reflected routes, prefer routes with shorter
cluster-id
Ø
Originator ID is the router-id of the ibgp
router that forwarded the route to the route-reflector
Ø
Cluster ID is the router-id of the
route-reflector
Default config include
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
network 20.20.20.0 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
network 40.40.40.0 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: Advertise ntwk 100.100.100.0 and 200.200.200.0 into
bgp.
Ensure reachability between 100.100.100.0/24 and 200.200.200.0/24 such that r1 only forms ibgp relationship with r2 and r3 only forms with r2 only.
Ensure reachability between 100.100.100.0/24 and 200.200.200.0/24 such that r1 only forms ibgp relationship with r2 and r3 only forms with r2 only.
Here R2
will be the route-reflector, i.e. it will form nei relationship with R1 and R3.
R1(config)# router bgp 100
nei 20.20.20.2
remote-as 222
nei 10.10.10.2
remote-as 100
R2(config)# router bgp 100
nei 10.10.10.1 remote-as
100
nei 30.30.30.1
remote-as 100
R3(config)# router bgp 100
nei 20.20.20.2
remote-as 222
nei 30.30.30.2
remote-as 100
Lets advertise 100.100.100.0/24 and
200.200.200.0/24
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:
If ISP2 advertises network 100.100.100.0, R1 will get it
(learnt via ebgp).R2 will get it (R1 will advertise it to R2 as an ibgp
route).R2 will not advertise it because route learnt via ibgp are not
advertised to other ibgp peers
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 since we cfged ntwk 20.20.20.0 0.0.0.255 area 0 in ospf fur router R1, 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
With next-hop-self, we are sure the next-hop will exist in the routing table irrespective of wheda we cfged 20.20.20.0 & 40.40.40.0 in ospf
With next-hop-self, we are sure the next-hop will exist in the routing table irrespective of wheda we cfged 20.20.20.0 & 40.40.40.0 in ospf
Here we can see that R2 is the only router getting both
100.100.100.0 and 200.200.200.0 routes.
R1# sh ip bgp
Network Next
Hop Metric LocPrf Weight Path
*> 100.100.100.0/24
20.20.20.2 0 0
222 i
R3# sh ip bgp
Network Next
Hop Metric LocPrf
Weight Path
*>
200.200.200.0 40.40.40.2 0 0
111 i
R2# sh ip bgp
Network Next
Hop Metric LocPrf Weight
Path
*>i100.100.100.0/24 10.10.10.1 0 100 0 222
i
*>i200.200.200.0 30.30.30.1 0 100 0 111
i
Hence
we need to configure route-reflector on R2 to reflect the routes
R2(config-router)# nei 10.10.10.1
route-reflector-client
nei 30.30.30.1
route-reflector-client
Lets only show the bgp table of R1
R1# sh ip bgp
Network Next
Hop Metric LocPrf Weight Path
*> 100.100.100.0/24 20.20.20.2 0 0 222
i
*>i200.200.200.0 30.30.30.1 0 100 0 111
i
R1(config-router)# do sh ip bgp 200.200.200.0
BGP routing table entry for 200.200.200.0/24, version
5
Paths: (1 available, best #1, table
Default-IP-Routing-Table)
30.30.30.1
(metric 128) from 10.10.10.2 (77.77.77.1)
Origin
IGP, metric 0, localpref 100, valid, internal, best
Originator: 99.99.99.1, Cluster
list: 77.77.77.1
This shows that we are
this router is a route-reflector-client
R2(config-router)# do sh ip bgp 200.200.200.0
BGP routing table
entry for 200.200.200.0/24, version 7
Paths: (1 available,
best #1, table Default-IP-Routing-Table)
111, (Received from a RR-client)
30.30.30.1 from 30.30.30.1 (99.99.99.1)
Origin IGP, metric 0, localpref 100,
valid, internal, best
This shows that R2 is
the route-reflector
Taskn 2) cfg the cluster-id on R2 as its loopback
add(default cfg)
R2(config-router)# bgp cluster-id 77.77.77.1
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