BGP Basic Configuration Example [ Step by step]

BGP Basic Configuration Example [ Step by step]


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 255.255.255.0


Note 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 Case Studies: Synchronization


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

Bilel-A

Enthusiastic Network Engineer specializing in Cisco ACI, passionate about solving challenges. A lifelong learner who loves gaining and sharing knowledge. Profile: https://www.linkedin.com/in/bilel-ameur-71116b2b5
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