BGP Basic Configuration Example [ Step by step]
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Topology
BGP Configuration
R1 Configuration:
R1#show run
Building configuration...
Current configuration : 799 bytes
version 15.4
hostname R1
interface Loopback0
ip address 1.1.1.1 255.255.255.255
!
interface GigabitEthernet0/0/0
ip address 8.8.8.1 255.255.255.0
duplex auto
speed auto
!
router bgp 65001
bgp log-neighbor-changes
no synchronization
neighbor 8.8.8.2 remote-as 65002
network 8.8.8.0 mask 255.255.255.0
network 1.1.1.1 mask 255.255.255.255
R2 Configuration:
R2#show running-config
Building configuration...
Current configuration : 846 bytes
!
version 15.4
no service timestamps log datetime msec
no service timestamps debug datetime msec
no service password-encryption
!
hostname R2
!
ip cef
no ipv6 cef
spanning-tree mode pvst
interface Loopback0
ip address 2.2.2.2 255.255.255.255
!
interface GigabitEthernet0/0/0
ip address 8.8.8.2 255.255.255.0
duplex auto
speed auto
!
router bgp 65002
bgp log-neighbor-changes
no synchronization
neighbor 8.8.8.1 remote-as 65001
network 2.2.2.2 mask 255.255.255.255
network 8.8.8.0 mask 255.255.255.0
network 15.1.1.0 mask 255.255.255.0Note about BGP “no synchronization”
If your AS passes traffic from another AS to a third AS, BGP should not advertise a route before all routers in your AS learn about the route via IGP.
BGP waits until IGP propagates the route within the AS and then advertises it to external peers. A BGP router with synchronization enabled does not install iBGP learned routes into its routing table if it is not able to validate those routes in its IGP.
Issue the no synchronization command under router bgp in order to disable synchronization. This prevents BGP from validating iBGP routes in IGP.
BGP peering Verifications
- Show ip bgp neighbor:
R1:
R1#show ip bgp neighbors
BGP neighbor is 8.8.8.2, remote AS 65002, external link
BGP version 4, remote router ID 2.2.2.2
BGP state = Established, up for 00:47:17
Last read 00:47:17, last write 00:47:17, hold time is 180, keepalive interval is 60 seconds
Neighbor capabilities:
Route refresh: advertised and received(new)
Address family IPv4 Unicast: advertised and received
Message statistics:
InQ depth is 0
OutQ depth is 0
Sent Rcvd
Opens: 1 1
Notifications: 0 0
Updates: 3 3
Keepalives: 48 48
Route Refresh: 0 0
Total: 52 52
Default minimum time between advertisements runs is 30 seconds
For address family: IPv4 Unicast
BGP table version 6, neighbor version 6/0
Output queue size : 0
Index 1, Offset 0, Mask 0x2
1 update-group member
Sent Rcvd
Prefix activity: ---- ----
Prefixes Current: 3 3 (Consumes 138 bytes)
Prefixes total: 3 3
Implicit Withdraw: 0 0
Explicit Withdraw: 0 0
Used as bestpath: n/a 1
Used as multipath: n/a 0
Outbound Inbound
Local Policy Denied Prefixes: -------- -------
Total: 0 0
Number of NLRIs in the update sent: max 3, min 1
Address tracking is enabled, the RIB does have a route to 8.8.8.2
Connections established 1; dropped 3
Last reset never
Transport(tcp) path-mtu-discovery is enabled
Connection state is ESTAB, I/O status: 1, unread input bytes: 0
Connection is ECN Disabled, Minimum incoming TTL 0, Outgoing TTL 1
Local host: 8.8.8.1, Local port: 179
Foreign host: 8.8.8.2, Foreign port: 1025
Connection tableid (VRF): 0
Enqueued packets for retransmit: 0, input: 0 mis-ordered: 0 (0 bytes)
Event Timers (current time is 0xC69F4):
Timer Starts Wakeups Next
Retrans 0 0 0x0
TimeWait 0 0 0x0
AckHold 51 0 0x0
SendWnd 0 0 0x0
KeepAlive 48 0 0x0
GiveUp 0 0 0x0
PmtuAger 0 0 0x0
DeadWait 0 0 0x0
Linger 0 0 0x0
ProcessQ 0 0 0x0
iss: 2057115318 snduna: 2057115748 sndnxt: 2057115748 sndwnd: 15955
irs: 3480424370 rcvnxt: 3480424751 rcvwnd: 16004 delrcvwnd: 380
SRTT: 259 ms, RTTO: 579 ms, RTV: 320 ms, KRTT: 0 ms
minRTT: 16 ms, maxRTT: 300 ms, ACK hold: 200 ms
Status Flags: passive open, gen tcbs
Option Flags: nagle, path mtu capable
IP Precedence value : 6
Datagrams (max data segment is 1460 bytes):
Rcvd: 52 (out of order: 0), with data: 0, total data bytes: 0
Sent: 49 (retransmit: 0, fastretransmit: 0, partialack: 0, Second Congestion: 0), with data: 3, total data bytes: 72
Packets received in fast path: 0, fast processed: 0, slow path: 0
fast lock acquisition failures: 0, slow path: 0
R2:
R2#show ip bgp neighbors
BGP neighbor is 8.8.8.1, remote AS 65001, external link
BGP version 4, remote router ID 1.1.1.1
BGP state = Established, up for 00:48:42
Last read 00:48:42, last write 00:48:42, hold time is 180, keepalive interval is 60 seconds
Neighbor capabilities:
Route refresh: advertised and received(new)
Address family IPv4 Unicast: advertised and received
Message statistics:
InQ depth is 0
OutQ depth is 0
Sent Rcvd
Opens: 1 1
Notifications: 0 0
Updates: 3 3
Keepalives: 49 49
Route Refresh: 0 1
Total: 53 54
Default minimum time between advertisements runs is 30 seconds
For address family: IPv4 Unicast
BGP table version 6, neighbor version 6/0
Output queue size : 0
Index 1, Offset 0, Mask 0x2
1 update-group member
Sent Rcvd
Prefix activity: ---- ----
Prefixes Current: 3 2 (Consumes 115 bytes)
Prefixes total: 3 2
Implicit Withdraw: 0 0
Explicit Withdraw: 0 0
Used as bestpath: n/a 1
Used as multipath: n/a 0
Outbound Inbound
Local Policy Denied Prefixes: -------- -------
Total: 0 0
Number of NLRIs in the update sent: max 3, min 1
Address tracking is enabled, the RIB does have a route to 8.8.8.1
Connections established 1; dropped 0
Last reset never
Transport(tcp) path-mtu-discovery is enabled
Connection state is ESTAB, I/O status: 1, unread input bytes: 0
Connection is ECN Disabled, Minimum incoming TTL 0, Outgoing TTL 1
Local host: 8.8.8.2, Local port: 1025
Foreign host: 8.8.8.1, Foreign port: 179
Connection tableid (VRF): 0
Enqueued packets for retransmit: 0, input: 0 mis-ordered: 0 (0 bytes)
Event Timers (current time is 0xC69F4):
Timer Starts Wakeups Next
Retrans 0 0 0x0
TimeWait 0 0 0x0
AckHold 52 0 0x0
SendWnd 0 0 0x0
KeepAlive 49 0 0x0
GiveUp 0 0 0x0
PmtuAger 0 0 0x0
DeadWait 0 0 0x0
Linger 0 0 0x0
ProcessQ 0 0 0x0
iss: 2057115318 snduna: 2057115748 sndnxt: 2057115748 sndwnd: 15955
irs: 3480424370 rcvnxt: 3480424751 rcvwnd: 16004 delrcvwnd: 380
SRTT: 259 ms, RTTO: 579 ms, RTV: 320 ms, KRTT: 0 ms
minRTT: 16 ms, maxRTT: 300 ms, ACK hold: 200 ms
Status Flags: passive open, gen tcbs
Option Flags: nagle, path mtu capable
IP Precedence value : 6
Datagrams (max data segment is 1460 bytes):
Rcvd: 53 (out of order: 0), with data: 1, total data bytes: 24
Sent: 50 (retransmit: 0, fastretransmit: 0, partialack: 0, Second Congestion: 0), with data: 3, total data bytes: 72
Packets received in fast path: 0, fast processed: 0, slow path: 0
fast lock acquisition failures: 0, slow path: 0
R2#- Show ip BGP
R1#show ip bgp
BGP table version is 6, local router ID is 1.1.1.1
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
*> 1.1.1.1/32 0.0.0.0 0 0 32768 i
*> 2.2.2.2/32 8.8.8.2 0 0 0 65002 i
*> 8.8.8.0/24 0.0.0.0 0 0 32768 i
* 8.8.8.2 0 0 0 65002 i
*> 15.1.1.0/24 8.8.8.2 0 0 0 65002 i
R1#
------------------------------------------------------------------------
R2#show ip bgp
BGP table version is 8, local router ID is 2.2.2.2
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
*> 1.1.1.1/32 8.8.8.1 0 0 0 65001 i
*> 2.2.2.2/32 0.0.0.0 0 0 32768 i
*> 8.8.8.0/24 0.0.0.0 0 0 32768 i
* 8.8.8.1 0 0 0 65001 i
*> 15.1.1.0/24 0.0.0.0 0 0 32768 i- Show ip route:
R1#show ip route
Codes: L - local, 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, E - EGP
i - IS-IS, 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
1.0.0.0/32 is subnetted, 1 subnets
C 1.1.1.1/32 is directly connected, Loopback0
2.0.0.0/32 is subnetted, 1 subnets
B 2.2.2.2/32 [20/0] via 8.8.8.2, 00:00:00
8.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
C 8.8.8.0/24 is directly connected, GigabitEthernet0/0/0
L 8.8.8.1/32 is directly connected, GigabitEthernet0/0/0
15.0.0.0/24 is subnetted, 1 subnets
B 15.1.1.0/24 [20/0] via 8.8.8.2, 00:00:00
------------------------------
R2# show ip route
Codes: L - local, 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, E - EGP
i - IS-IS, 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
1.0.0.0/32 is subnetted, 1 subnets
B 1.1.1.1/32 [20/0] via 8.8.8.1, 00:00:00
2.0.0.0/32 is subnetted, 1 subnets
C 2.2.2.2/32 is directly connected, Loopback0
8.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
C 8.8.8.0/24 is directly connected, GigabitEthernet0/0/0
L 8.8.8.2/32 is directly connected, GigabitEthernet0/0/0
15.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
C 15.1.1.0/24 is directly connected, GigabitEthernet0/0/1
L 15.1.1.1/32 is directly connected, GigabitEthernet0/0/1
