Here am going show you how to aggregate the
network.
Note I changed the address scheme so that I
can aggregate the address.
R4#sh ip route 44.4.0.0 255.255.252.0
longer-prefixes
*Jan
9 00:47:18.382: %SYS-5-CONFIG_I: Configured from console by console
R4#sh ip bgp regexp ^$
BGP table version is 19, local router ID is
150.4.4.4
Status codes: s suppressed, d damped, h
history, * valid, > best, i - internal,
r RIB-failure, S Stale
Origin codes: i - IGP, e - EGP, ? -
incomplete
Network Next Hop Metric LocPrf Weight Path
*> 4.1.0.0/24 0.0.0.0 0 32768 i
*> 4.2.0.0/24 0.0.0.0 0 32768 i
*> 4.3.0.0/24 0.0.0.0 0 32768 i
*> 44.4.1.0/24 0.0.0.0 0 32768 ?
*> 44.4.2.0/24 0.0.0.0 0 32768 ?
*> 44.4.3.0/24 0.0.0.0 0 32768 ?
Here am going to aggregate all 44.4.x.x/24
network.
As aggregation we found 44.4.0.0 / 22.
Note: while doing
aggregation it should be must that one subnet should be present in the bgp
routing table. Then only the advertise aggregation will be propagated.
R4#sh ip route 44.4.0.0 255.255.252.0
longer-prefixes
Codes: C - connected, S - static, R - RIP,
M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2
i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * - candidate default, U - per-user static route
o - ODR, P - periodic downloaded static route
Gateway of last resort is not set
44.0.0.0/24 is subnetted, 3 subnets
C
44.4.1.0 is directly connected, Loopback11
C
44.4.2.0 is directly connected, Loopback12
C
44.4.3.0 is directly connected, Loopback13
So this is my valid aggregate address.
Hence lets configure the aggregate address.
R4(config)#router bgp 400
R4(config-router)#aggregate-address
44.4.0.0 255.255.252.0
R4#sh ip bgp regexp ^$
BGP table version is 20, local router ID is
150.4.4.4
Status codes: s suppressed, d damped, h
history, * valid, > best, i - internal,
r RIB-failure, S Stale
Origin codes: i - IGP, e - EGP, ? -
incomplete
Network Next Hop Metric LocPrf Weight Path
*> 4.1.0.0/24 0.0.0.0 0 32768 i
*> 4.2.0.0/24 0.0.0.0 0 32768 i
*> 4.3.0.0/24 0.0.0.0 0 32768 i
*> 44.4.0.0/22 0.0.0.0 32768 i
*> 44.4.1.0/24 0.0.0.0 0 32768 ?
*> 44.4.2.0/24 0.0.0.0 0 32768 ?
*> 44.4.3.0/24 0.0.0.0 0 32768 ?
R4#sh ip bgp 44.4.0.0/22
BGP routing table entry for 44.4.0.0/22,
version 20
Paths: (1 available, best #1, table
Default-IP-Routing-Table)
Advertised to update-groups:
1
Local, (aggregated by 400 150.4.4.4)
0.0.0.0 from 0.0.0.0 (150.4.4.4)
Origin IGP, localpref 100, weight 32768, valid, aggregated, local,
atomic-aggregate, best
This information gives us the details about
the who is aggregate this prefixes. This will be helpful when the R4 again
receive its own aggregate address it will not consider that update by seeing
this value.
Now lets check on R6 and try to reach this
prefix form R6.
R6#sh ip bgp 44.4.0.0/22
BGP routing table entry for 44.4.0.0/22,
version 110
Paths: (1 available, best #1, table
Default-IP-Routing-Table)
Not
advertised to any peer
100
400, (aggregated by 400 150.4.4.4)
155.1.16.1 from 155.1.16.1 (150.1.1.1)
Origin IGP, localpref 100, valid, external, atomic-aggregate, best
R6#sh ip bgp | in 44.4
*> 44.4.0.0/22 155.1.16.1 0 100 400 i
*> 44.4.1.0/24 155.1.16.1 0 100 400 ?
*> 44.4.2.0/24 155.1.16.1 0 100 400 ?
*> 44.4.3.0/24 155.1.16.1 0 100 400 ?
See we got all the updates including the
aggregate address.
Summary only command is used to advertise
only the summary address.
R4#sh run | s router bgp
router bgp 400
no
synchronization
bgp
log-neighbor-changes
network 4.1.0.0 mask 255.255.255.0
network 4.2.0.0 mask 255.255.255.0
network 4.3.0.0 mask 255.255.255.0
aggregate-address
44.4.0.0 255.255.252.0 summary-only
redistribute eigrp 1 route-map 44_network
neighbor 150.5.5.5 remote-as 500
neighbor 150.5.5.5 ttl-security hops 2
neighbor 150.5.5.5 update-source Loopback0
neighbor 155.1.34.3 remote-as 100
no
auto-summary
R4#sh ip bgp regexp ^$
BGP table version is 25, local router ID is
150.4.4.4
Status codes: s suppressed, d damped, h
history, * valid, > best, i - internal,
r RIB-failure, S Stale
Origin codes: i - IGP, e - EGP, ? -
incomplete
Network Next Hop Metric LocPrf Weight Path
*> 4.1.0.0/24 0.0.0.0 0 32768 i
*> 4.2.0.0/24 0.0.0.0 0 32768 i
*> 4.3.0.0/24 0.0.0.0 0
32768 i
*> 44.4.0.0/22 0.0.0.0 32768 i
s> 44.4.1.0/24 0.0.0.0 0 32768 ?
s> 44.4.2.0/24 0.0.0.0 0 32768 ?
s> 44.4.3.0/24 0.0.0.0 0
32768 ?
Note this s indicates suppressed. So lets
check on R6 router.
R6#sh ip bgp | in 44.4
*> 44.4.0.0/22 155.1.16.1 0 100 400 I
R6#traceroute 44.4.1.4 source loopback 1
Type escape sequence to abort.
Tracing the route to 44.4.1.4
1
155.1.16.1 4 msec 84 msec 48 msec
2
155.1.123.3 200 msec 244 msec 124 msec
3
155.1.34.4 208 msec * 152 msec
Note the summary only command effect all
the peer internal and external peers.
Now lets do more interesting with
aggregation
R1#sh ip bgp ne 150.3.3.3 advertised-routes
BGP table version is 121, local router ID
is 150.1.1.1
Status codes: s suppressed, d damped, h
history, * valid, > best, i - internal,
r RIB-failure, S Stale
Origin codes: i - IGP, e - EGP, ? -
incomplete
Network Next Hop Metric LocPrf Weight Path
*> 6.1.0.0/16 155.1.16.6 0 0 600 i
*> 6.2.0.0/16 155.1.16.6 0 0 600 i
*> 6.3.0.0/16 155.1.16.6 0 0 600 i
*> 150.1.1.0/24 0.0.0.0 0 32768 i
*> 150.2.2.0/24 155.1.123.2 2 32768 i
*> 150.3.3.0/24 155.1.123.3 2 32768 i
Total number of prefixes 6
R1#sh ip bgp ne 150.2.2.2 advertised-routes
BGP table version is 121, local router ID
is 150.1.1.1
Status codes: s suppressed, d damped, h
history, * valid, > best, i - internal,
r RIB-failure, S Stale
Origin codes: i - IGP, e - EGP, ? -
incomplete
Network Next Hop Metric LocPrf Weight Path
*> 6.1.0.0/16 155.1.16.6 0 0 600 i
*> 6.2.0.0/16 155.1.16.6 0 0 600 i
*> 6.3.0.0/16 155.1.16.6 0 0 600 i
*> 150.1.1.0/24 0.0.0.0 0 32768 i
*> 150.2.2.0/24 155.1.123.2 2 32768 i
*> 150.3.3.0/24 155.1.123.3 2 32768 i
Total number of prefixes 6
So here R1 sending updates to R2 and R3
about 6.x.x.x/16 and 150.x.x.x/24 network. Here what am going to do is one
neighbor going to get only the aggregate route and another neighbor will get
the another aggregate routes.
So R1 going to aggregate 6.x.x.x/16 network
to R2 and 150.x.x.x/24 network to R3.
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