Di Posting Oleh : Simple Learning
Kategori : BGP Core Technologies Routing
Prerequisites: CCNP level skills.
Topology
Note!
Use Lab 81 configuration to complete this lab.
Pic. 1 - Topology Diagram.
Icons designed by: Andrzej Szoblik - http://www.newo.pl
Task 1
Configure EBGP session between R3 and R5.
Task 2
Advertise loopback addresses into BGP on R1, R3 and R5. On R5 do not use the 'network' statement. Ensure the reachability between the advertised subnets.
Lab Solution
Task 1
Configure EBGP session between R3 and R5.
R3 Configuration:
!
router bgp 13
no synchronization
bgp router-id 3.3.3.3
bgp log-neighbor-changes
neighbor 10.1.35.5 remote-as 50
neighbor 172.16.101.1 remote-as 13
neighbor 172.16.101.1 update-source Loopback0
no auto-summary
no synchronization
bgp router-id 3.3.3.3
bgp log-neighbor-changes
neighbor 10.1.35.5 remote-as 50
neighbor 172.16.101.1 remote-as 13
neighbor 172.16.101.1 update-source Loopback0
no auto-summary
!
R5 Configuration:
!
router bgp 50
no synchronization
bgp router-id 5.5.5.5
bgp log-neighbor-changes
neighbor 10.1.35.3 remote-as 13
no auto-summary
no synchronization
bgp router-id 5.5.5.5
bgp log-neighbor-changes
neighbor 10.1.35.3 remote-as 13
no auto-summary
!
Verification:
Pic. 2 - EBGP Session between R3 and R5.
Pic. 3 - Neighbor Details.
Task 2
Advertise loopback addresses into BGP on R1, R3 and R5. On R5 don not use 'network' statement. Ensure the reachability between the advertised subnets.
R1 Configuration:
!
router bgp 13
no synchronization
bgp router-id 1.1.1.1
bgp log-neighbor-changes
network 172.16.101.0 mask 255.255.255.0
neighbor 172.16.103.3 remote-as 13
neighbor 172.16.103.3 update-source Loopback0
no auto-summary
no synchronization
bgp router-id 1.1.1.1
bgp log-neighbor-changes
network 172.16.101.0 mask 255.255.255.0
neighbor 172.16.103.3 remote-as 13
neighbor 172.16.103.3 update-source Loopback0
no auto-summary
!
Notice!
'Network' statement in BGP does advertise the networks (unlike in IGP protocols). The network/subnet must have the EXACT match in the routing table (network/network_mask). If the subnet is being advertised (not a major class), the 'mask' keyword must be used.
Verification:
Pic. 4 - R1's BGP Table.
Subnets advertised locally always set the two BGP attributes as
- Next-Hop = 0.0.0.0
- Weight = 32768
- Path = empty
Pic. 5 - R3 Receives the Prefix.
R3 receives 172.16.101.0/24 but is marked as RIB-Failure. This is due to the fact that Administrative Distance of IBGP is 200, and the same prefix is advertised by OSPF with the Administrative Distance 110.
Notice!
Next-hop attribute point to the source of BGP advertisements (R1's Loopback0): 172.16.101.1.Notice!
R3 automatically assigns Local Preference: 100. The same Local Preference value is assigned by R1 (originator of the prefix). This can be seen on R1 using this command:
Pic. 6 - R1's BGP Prefix Details.
Pic 7 - R5 Receives the Prefix
R3 advertising the prefix to an EBGP neighbor, prepends the AS (13).
R3 Configuration:
!
router bgp 13
no synchronization
bgp router-id 3.3.3.3
bgp log-neighbor-changes
network 172.16.103.0 mask 255.255.255.0
neighbor 10.1.35.5 remote-as 50
neighbor 172.16.101.1 remote-as 13
neighbor 172.16.101.1 update-source Loopback0
no auto-summary
no synchronization
bgp router-id 3.3.3.3
bgp log-neighbor-changes
network 172.16.103.0 mask 255.255.255.0
neighbor 10.1.35.5 remote-as 50
neighbor 172.16.101.1 remote-as 13
neighbor 172.16.101.1 update-source Loopback0
no auto-summary
!
R5 Configuration:
!
ip prefix-list LO seq 5 permit 172.16.105.0/24
!
route-map CONN_TO_BGP permit 10
match ip address prefix-list LO
!
match ip address prefix-list LO
!
router bgp 50
no synchronization
bgp router-id 5.5.5.5
bgp log-neighbor-changes
redistribute connected route-map CONN_TO_BGP
neighbor 10.1.35.3 remote-as 13
no auto-summary
no synchronization
bgp router-id 5.5.5.5
bgp log-neighbor-changes
redistribute connected route-map CONN_TO_BGP
neighbor 10.1.35.3 remote-as 13
no auto-summary
!
Verification:
Pic. 8 - Prefix Redistributed into BGP on R5.
The origin attribute for BGP redistributed prefixes is set to '?' = incomplete.
Notice!
R1 is going to have problem with the reachability to 172.16.105.0/24. The next-hop attribute set by EBGP peer (BGP neighbor) is not changed (except for connections in the same broadcast domain). R1 has no reachability to the next-hop 10.1.35.5.
Pic. 9 - R1's Next-Hop Inaccessible.
Pic. 10 - Detailed Output.
R3 Configuration:
!
router bgp 13
no synchronization
bgp router-id 3.3.3.3
bgp log-neighbor-changes
network 172.16.103.0 mask 255.255.255.0
neighbor 10.1.35.5 remote-as 50
neighbor 172.16.101.1 remote-as 13
neighbor 172.16.101.1 update-source Loopback0
neighbor 172.16.101.1 next-hop-self
no auto-summary
no synchronization
bgp router-id 3.3.3.3
bgp log-neighbor-changes
network 172.16.103.0 mask 255.255.255.0
neighbor 10.1.35.5 remote-as 50
neighbor 172.16.101.1 remote-as 13
neighbor 172.16.101.1 update-source Loopback0
neighbor 172.16.101.1 next-hop-self
no auto-summary
!
Pic. 11 - Next-Hop Address Changed.
Pic. 12 - Proper Ping Test.
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