Some Hard Knowledge of BGP Community Local-AS.

AS a well-known BGP community in the IT industry, Local-AS is used in confederations scenarios to prevent transmitting traffic outside the local-as. if you don’t know what BGP community is and how to work, and I will give you a suggestion to read several articles about BGP first before you want to continue to understand the CCIE RS Lab which SPOTO is committed to. SPOTO will provide some free study materials and you can download them to help your certification exam.

Let see the configuration for better understanding, we are continuing our previous topology.

Topology:-

Goal:

·configure the topology as per the diagram and assign the IP addresses.

·configure iBGP and EBGP neighborship.

·configure router 2 to advertise 12.0.0.0/24 prefix all the routers within the AS 650123.

R1#show ip interface brief

Interface IP-Address OK? Method Status Protocol

FastEthernet0/0 10.1.1.1 YES manual up up

Serial3/0 1.1.1.1 YES manual up up

Serial3/3 4.1.1.2 YES manual up up

Loopback0 11.0.0.1 YES manual up up

R2#show ip interface brief

Interface IP-Address OK? Method Status Protocol

FastEthernet0/0 20.1.1.1 YES manual up up

Serial3/0 1.1.1.2 YES manual up up

Serial3/1 2.1.1.1 YES manual up up

Loopback0 12.0.0.1 YES manual up up

R3#show ip interface brief

Interface IP-Address OK? Method Status Protocol

FastEthernet0/0 30.1.1.1 YES manual up up

Serial3/1 2.1.1.2 YES manual up up

Serial3/2 3.1.1.1 YES manual up up

Loopback0 13.0.0.1 YES manual up up

R4#show ip interface brief

Interface IP-Address OK? Method Status Protocol

FastEthernet0/0 40.1.1.1 YES manual up up

Serial3/2 3.1.1.2 YES manual up up

Serial3/3 4.1.1.1 YES manual up up

Loopback0 14.0.0.1 YES manual up up

R5#show ip interface brief

Interface IP-Address OK? Method Status Protocol

FastEthernet0/0 10.1.1.2 YES manual up up

Loopback0 15.0.0.1 YES manual up up

R6#show ip interface brief

Interface IP-Address OK? Method Status Protocol

FastEthernet0/0 30.1.1.2 YES manual up up

Loopback0 16.0.0.1 YES manual up up

R1(config)#router bgp 650123

R1(config-router)#neighbor 1.1.1.2 remote-as 650123

R1(config-router)#neighbor 10.1.1.2 remote-as 650005

R1(config-router)#neighbor 4.1.1.1 remote-as 650004

R1(config-router)#neighbor 2.1.1.2 remote-as 650123

R1(config-router)#neighbor 2.1.1.2 next-hop-self

R1(config-router)#neighbor 1.1.1.2 next-hop-self

R1(config-router)#network 10.0.0.0

R1(config-router)#network 1.0.0.0

R1(config-router)#network 4.0.0.0

R1(config-router)#network 11.0.0.0 mask 255.255.255.0

R1(config-router)#no auto-summary

R1(config-router)#no synchronization

R1(config-router)#exit

R2(config)#router bgp 650123

R2(config-router)#neighbor 1.1.1.1 remote-as 650123

*Jan 26 13:34:05.043: %BGP-5-ADJCHANGE: neighbor 1.1.1.1 Up

R2(config-router)#neighbor 2.1.1.2 remote-as 650123

R2(config-router)#network 20.0.0.0

R2(config-router)#network 2.0.0.0

R2(config-router)#network 1.0.0.0

R2(config-router)#network 12.0.0.0 mask 255.255.255.0

R2(config-router)#no synchronization

R2(config-router)#no auto-summary

R2(config-router)#exit

R3(config)#router bgp 650123

R3(config-router)#neighbor 2.1.1.1 remote-as 650123

*Jan 26 13:36:03.887: %BGP-5-ADJCHANGE: neighbor 2.1.1.1 Up

R3(config-router)#neighbor 30.1.1.2 remote-as 650006

R3(config-router)#neighbor 1.1.1.1 remote-as 650123

*Jan 26 14:00:00.539: %BGP-5-ADJCHANGE: neighbor 1.1.1.1 Up

R3(config-router)#neighbor 1.1.1.1 next-hop-self

R3(config-router)#neighbor 2.1.1.1 next-hop-self

R3(config-router)#network 2.0.0.0

R3(config-router)#network 3.0.0.0

R3(config-router)#network 30.0.0.0

R3(config-router)#network 13.0.0.0 mask 255.255.255.0

R3(config-router)#no synchronization

R3(config-router)#no auto-summary

R3(config-router)#exit

R4(config)#router bgp 650004

R4(config-router)#neighbor 3.1.1.1 remote 650123

*Jan 26 13:30:57.211: %BGP-5-ADJCHANGE: neighbor 3.1.1.1 Up

R4(config-router)#neighbor 4.1.1.2 remote 650123

*Jan 26 13:31:14.247: %BGP-5-ADJCHANGE: neighbor 4.1.1.2 Up

R4(config-router)#network 4.0.0.0

R4(config-router)#network 3.0.0.0

R4(config-router)#network 40.0.0.0

R4(config-router)#network 14.0.0.0 mask 255.255.255.0

R4(config-router)#no auto-summary

R4(config-router)#no synchronization

R4(config-router)#exit

R5(config)#router bgp 650005

R5(config-router)#neighbor 10.1.1.1 remote-as 650123

R5(config-router)#network 10.0.0.0

*Jan 26 13:31:08.975: %BGP-5-ADJCHANGE: neighbor 10.1.1.1 Up

R5(config-router)#network 15.0.0.0 mask 255.255.255.0

R5(config-router)#no auto-summary

R5(config-router)#no synchronization

R5(config-router)#exit

R6(config)#router bgp 650006

R6(config-router)#neighbor 30.1.1.1 remote-as 650123

*Jan 26 13:31:00.731: %BGP-5-ADJCHANGE: neighbor 30.1.1.1 Up

R6(config-router)#network 16.0.0.0 mask 255.255.255.0

R6(config-router)#network 30.0.0.0

R6(config-router)#no auto-summary

R6(config-router)#no synchronization

R6(config-router)#exit

R1#show ip bgp summary

BGP router identifier 11.0.0.1, local AS number 650123

BGP table version is 24, main routing table version 24

14 network entries using 2016 bytes of memory

21 path entries using 1680 bytes of memory

6/5 BGP path/bestpath attribute entries using 816 bytes of memory

3 BGP AS-PATH entries using 72 bytes of memory

0 BGP route-map cache entries using 0 bytes of memory

0 BGP filter-list cache entries using 0 bytes of memory

BGP using 4584 total bytes of memory

BGP activity 14/0 prefixes, 30/9 paths, scan interval 60 secs

Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd

1.1.1.2 4 650123 40 45 24 0 0 00:30:07 4

2.1.1.2 4 650123 10 11 24 0 0 00:01:10 7

4.1.1.1 4 650004 34 33 24 0 0 00:22:46 4

10.1.1.2 4 650005 27 35 24 0 0 00:20:32 2

R2#show ip bgp summary

BGP router identifier 12.0.0.1, local AS number 650123

BGP table version is 20, main routing table version 20

14 network entries using 2016 bytes of memory

19 path entries using 1520 bytes of memory

5/5 BGP path/bestpath attribute entries using 680 bytes of memory

3 BGP AS-PATH entries using 72 bytes of memory

0 BGP route-map cache entries using 0 bytes of memory

0 BGP filter-list cache entries using 0 bytes of memory

BGP using 4288 total bytes of memory

BGP activity 14/0 prefixes, 23/4 paths, scan interval 60 secs

Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd

1.1.1.1 4 650123 46 41 20 0 0 00:31:05 7

2.1.1.2 4 650123 46 38 20 0 0 00:29:07 8

R3#show ip bgp summary

BGP router identifier 13.0.0.1, local AS number 650123

BGP table version is 38, main routing table version 38

14 network entries using 2016 bytes of memory

21 path entries using 1680 bytes of memory

6/5 BGP path/bestpath attribute entries using 816 bytes of memory

3 BGP AS-PATH entries using 72 bytes of memory

0 BGP route-map cache entries using 0 bytes of memory

0 BGP filter-list cache entries using 0 bytes of memory

BGP using 4584 total bytes of memory

BGP activity 14/0 prefixes, 38/17 paths, scan interval 60 secs

Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd

1.1.1.1 4 650123 10 10 38 0 0 00:00:08 7

2.1.1.1 4 650123 40 48 38 0 0 00:30:12 4

3.1.1.2 4 650004 33 39 33 0 0 00:25:07 4

30.1.1.2 4 650006 27 37 33 0 0 00:20:53 2

R4#show ip bgp summary

BGP router identifier 14.0.0.1, local AS number 650004

BGP table version is 17, main routing table version 17

14 network entries using 2016 bytes of memory

24 path entries using 1920 bytes of memory

5/5 BGP path/bestpath attribute entries using 680 bytes of memory

3 BGP AS-PATH entries using 72 bytes of memory

0 BGP route-map cache entries using 0 bytes of memory

0 BGP filter-list cache entries using 0 bytes of memory

BGP using 4688 total bytes of memory

BGP activity 14/0 prefixes, 36/12 paths, scan interval 60 secs

Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd

3.1.1.1 4 650123 41 33 17 0 0 00:25:28 8

4.1.1.2 4 650123 40 37 17 0 0 00:25:11 12

R5#show ip bgp summary

BGP router identifier 15.0.0.1, local AS number 650005

BGP table version is 32, main routing table version 32

14 network entries using 2016 bytes of memory

15 path entries using 1200 bytes of memory

5/5 BGP path/bestpath attribute entries using 680 bytes of memory

3 BGP AS-PATH entries using 72 bytes of memory

0 BGP route-map cache entries using 0 bytes of memory

0 BGP filter-list cache entries using 0 bytes of memory

BGP using 3968 total bytes of memory

BGP activity 20/6 prefixes, 21/6 paths, scan interval 60 secs

Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd

10.1.1.1 4 650123 41 30 32 0 0 00:23:19 13

R1#show ip bgp 15.0.0.1

BGP routing table entry for 15.0.0.0/24, version 12

Paths: (1 available, best #1, table default)

Advertised to update-groups:

2 3

Refresh Epoch 1

650005

10.1.1.2 from 10.1.1.2 (15.0.0.1)

Origin IGP, metric 0, localpref 100, valid, external, best

rx pathid: 0, tx pathid: 0x0

R2#show ip bgp 15.0.0.1

BGP routing table entry for 15.0.0.0/24, version 19

Paths: (1 available, best #1, table default)

Not advertised to any peer

Refresh Epoch 1

650005

1.1.1.1 from 1.1.1.1 (11.0.0.1)

Origin IGP, metric 0, localpref 100, valid, internal, best

rx pathid: 0, tx pathid: 0x0

R3#show ip bgp 15.0.0.1

BGP routing table entry for 15.0.0.0/24, version 122

Paths: (1 available, no best path)

Flag: 0x820

Not advertised to any peer

Refresh Epoch 2

650005

1.1.1.1 (inaccessible) from 1.1.1.1 (11.0.0.1)

Origin IGP, metric 0, localpref 100, valid, internal

rx pathid: 0, tx pathid: 0

(now we are going to configure router 2 to advertise 12.0.0.0/24 prefix all the routers within the AS 650123, make sure it will not cross the AS)

R4#show ip bgp 12.0.0.1

BGP routing table entry for 12.0.0.0/24, version 10

Paths: (1 available, best #1, table default)

Advertised to update-groups:

Refresh Epoch 1

650123

4.1.1.2 from 4.1.1.2 (12.0.0.1)

Origin IGP, metric 0, localpref 100, valid, external, best

rx pathid: 0, tx pathid: 0x0

R6#show ip bgp 12.0.0.1

BGP routing table entry for 12.0.0.0/24, version 6

Paths: (1 available, best #1, table default)

Not advertised to any peer

Refresh Epoch 2

650123

30.1.1.1 from 30.1.1.1 (13.0.0.1)

Origin IGP, localpref 100, valid, external, best

rx pathid: 0, tx pathid: 0x0

[AS_650004 and AS_650006 is getting 12.0.0.1/24 prefixe]

R2(config)#access-list 12 permit 12.0.0.0 0.0.0.255

R2(config)#route-map local-as permit 12

R2(config-route-map)#match ip address 12

R2(config-route-map)#set community local-AS

R2(config-route-map)#exit

R2(config)#route-map local-as permit 120

R2(config-route-map)#exit

R2(config)#router bgp 650123

R2(config-router)#no network 12.0.0.0 mask 255.255.255.0

R2(config-router)#network 12.0.0.0 mask 255.255.255.0 route-map local-as

R2(config-router)#neighbor 1.1.1.1 send-community

R2(config-router)#neighbor 2.1.1.2 send-community

R2(config-router)#end

R3#show ip bgp 12.0.0.1

BGP routing table entry for 12.0.0.0/24, version 52

Paths: (1 available, best #1, table default, not advertised outside local AS)

Not advertised to any peer

Refresh Epoch 3

Local

2.1.1.1 from 2.1.1.1 (12.0.0.1)

Origin IGP, metric 0, localpref 100, valid, internal, best

Community: local-AS

rx pathid: 0, tx pathid: 0x0

R1#show ip bgp 12.0.0.1

BGP routing table entry for 12.0.0.0/24, version 125

Paths: (1 available, best #1, table default, not advertised outside local AS)

Not advertised to any peer

Refresh Epoch 1

Local

1.1.1.2 from 1.1.1.2 (12.0.0.1)

Origin IGP, metric 0, localpref 100, valid, internal, best

Community: local-AS

rx pathid: 0, tx pathid: 0x0

(from the above output we can see all routers in AS 650123 is getting 12.0.0.0/24 prefixe, lets see AS 650006 and 650004)

R4#show ip bgp 12.0.0.1

% Network not in table

[from AS_650004]

R6#sh ip bgp 12.0.0.1

% Network not in table

[from AS_650006]

R5#show ip bgp 12.0.0.1

% Network not in table

[from AS_650005]

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