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43-H3C_BGP_Route_Selection_Configuration_Examples

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Introduction

This document provides examples for configuring BGP route selection based on route attributes.

Prerequisites

The configuration examples in this document were created and verified in a lab environment, and all the devices were started with the factory default configuration. When you are working on a live network, make sure you understand the potential impact of every command on your network.

This document assumes that you have basic knowledge of BGP and routing policy.

Example: Configuring route selection based on the AS_PATH attribute

Network configuration

As shown in Figure 1, all devices run BGP. Configure a routing policy on Device B and Device C to ensure that traffic from AS 100 to AS 400 is preferentially forwarded by Device D.

Figure 1 Network diagram

‌

Analysis

For devices in AS 100 to select the optimal route based on AS numbers, increase the local preference for routes whose AS_PATH attributes end with the specified AS number. Configure a routing policy on Device C to set the local preference to 300 for routes whose AS_PATH attributes end with AS number 400.

To filter routes based on AS numbers, use an AS path list.

Procedures

Configuring IP addresses for interfaces

# Configure an IP address for interface Ten-GigabitEthernet 3/1/1 on Device A.

<DeviceA> system-view

[DeviceA] interface ten-gigabitethernet 3/1/1

[DeviceA-Ten-GigabitEthernet3/1/1] ip address 12.12.12.1 24

[DeviceA-Ten-GigabitEthernet3/1/1] quit

# Configure IP addresses for other interfaces as shown in Figure 1. (Details not shown.)

Configuring BGP connections

# On Device A, enable the default BGP instance, set the AS number to 100, and specify 12.12.12.2 and 13.13.13.3 as BGP peers.

[DeviceA] bgp 100

[DeviceA-bgp-default] router-id 1.1.1.1

[DeviceA-bgp-default] peer 12.12.12.2 as-number 100

[DeviceA-bgp-default] peer 13.13.13.3 as-number 100

[DeviceA-bgp-default] address-family ipv4 unicast

[DeviceA-bgp-default-ipv4] peer 12.12.12.2 enable

[DeviceA-bgp-default-ipv4] peer 13.13.13.3 enable

[DeviceA-bgp-default-ipv4] quit

[DeviceA-bgp-default] quit

# On Device B, enable the default BGP instance, set the AS number to 100, specify 12.12.12.1 and 24.24.24.4 as BGP peers, and redistribute direct routes.

[DeviceB] bgp 100

[DeviceB-bgp-default] router-id 2.2.2.2

[DeviceB-bgp-default] peer 12.12.12.1 as-number 100

[DeviceB-bgp-default] peer 24.24.24.4 as-number 200

[DeviceB-bgp-default] address-family ipv4 unicast

[DeviceB-bgp-default-ipv4] peer 12.12.12.1 enable

[DeviceB-bgp-default-ipv4] peer 24.24.24.4 enable

[DeviceB-bgp-default-ipv4] import-route direct

[DeviceB-bgp-default-ipv4] quit

[DeviceB-bgp-default] quit

# On Device C, enable the default BGP instance, set the AS number to 100, specify 13.13.13.1 and 35.35.35.5 as BGP peers, and redistribute direct routes.

[DeviceC] bgp 100

[DeviceC-bgp-default] router-id 3.3.3.3

[DeviceC-bgp-default] peer 13.13.13.1 as-number 100

[DeviceC-bgp-default] peer 35.35.35.5 as-number 300

[DeviceC-bgp-default] address-family ipv4 unicast

[DeviceC-bgp-default-ipv4] peer 13.13.13.1 enable

[DeviceC-bgp-default-ipv4] peer 35.35.35.5 enable

[DeviceC-bgp-default-ipv4] import-route direct

[DeviceC-bgp-default-ipv4] quit

[DeviceC-bgp-default] quit

# On Device D, enable the default BGP instance, set the AS number to 200, specify 24.24.24.2 and 46.46.46.6 as BGP peers, and advertise the route 4.4.4.4/32.

[DeviceD] bgp 200

[DeviceD-bgp-default] router-id 4.4.4.4

[DeviceD-bgp-default] peer 24.24.24.2 as-number 100

[DeviceD-bgp-default] peer 46.46.46.6 as-number 400

[DeviceD-bgp-default] address-family ipv4 unicast

[DeviceD-bgp-default-ipv4] peer 24.24.24.2 enable

[DeviceD-bgp-default-ipv4] peer 46.46.46.6 enable

[DeviceD-bgp-default-ipv4] network 4.4.4.4 32

[DeviceD-bgp-default-ipv4] quit

[DeviceD-bgp-default] quit

# On Device E, enable the default BGP instance, set the AS number to 300, specify 35.35.35.3 and 56.56.56.6 as BGP peers, and advertise the route 5.5.5.5/32.

[DeviceE] bgp 300

[DeviceE-bgp-default] router-id 5.5.5.5

[DeviceE-bgp-default] peer 35.35.35.3 as-number 100

[DeviceE-bgp-default] peer 56.56.56.6 as-number 400

[DeviceE-bgp-default] address-family ipv4 unicast

[DeviceE-bgp-default-ipv4] peer 35.35.35.3 enable

[DeviceE-bgp-default-ipv4] peer 56.56.56.6 enable

[DeviceE-bgp-default-ipv4] network 5.5.5.5 32

[DeviceE-bgp-default-ipv4] quit

[DeviceE-bgp-default] quit

# On Device F, enable the default BGP instance, set the AS number to 400, specify 46.46.46.4 and 56.56.56.5 as BGP peers, and advertise the route 6.6.6.6/32.

[DeviceF] bgp 400

[DeviceF-bgp-default] router-id 6.6.6.6

[DeviceF-bgp-default] peer 46.46.46.4 as-number 200

[DeviceF-bgp-default] peer 56.56.56.5 as-number 300

[DeviceF-bgp-default] address-family ipv4 unicast

[DeviceF-bgp-default-ipv4] peer 46.46.46.4 enable

[DeviceF-bgp-default-ipv4] peer 56.56.56.5 enable

[DeviceF-bgp-default-ipv4] network 6.6.6.6 32

[DeviceF-bgp-default-ipv4] quit

[DeviceF-bgp-default] quit

# Display the BGP routing table on Device A. The output shows the routes advertised by Device D, Device E, and Device F, and the AS_PATH attributes of the routes.

[DeviceA] display bgp routing-table ipv4

Total number of routes: 12

BGP local router ID is 1.1.1.1

Status codes: * - valid, > - best, d - dampened, h - history

s - suppressed, S - stale, i - internal, e – external

a - additional-path

Origin: i - IGP, e - EGP, ? - incomplete

Network NextHop MED LocPrf PrefVal Path/Ogn

* >i 2.2.2.2/32 12.12.12.2 0 100 0 ?

* >i 3.3.3.3/32 13.13.13.3 0 100 0 ?

* >i 4.4.4.4/32 24.24.24.4 0 100 0 200i

* i 35.35.35.5 100 0 300 400

200i

* >i 5.5.5.5/32 35.35.35.5 0 100 0 300i

* i 24.24.24.4 100 0 200 400

300i

* >i 6.6.6.6/32 24.24.24.4 100 0 200 400i

* i 35.35.35.5 100 0 300 400i

* >i 12.12.12.0/24 12.12.12.2 0 100 0 ?

* >i 13.13.13.0/24 13.13.13.3 0 100 0 ?

* >i 24.24.24.0/24 12.12.12.2 0 100 0 ?

* >i 35.35.35.0/24 13.13.13.3 0 100 0 ?

Configuring routing policies

# Create routing policy aspath on Device C, and set the local preference to 300 for routes whose AS_PATH attributes end with AS number 400.

[DeviceC] ip as-path 1 permit 400$

[DeviceC] route-policy aspath permit node 20

[DeviceC-route-policy-aspath-20] if-match as-path 1

[DeviceC-route-policy-aspath-20] apply local-preference 300

[DeviceC-route-policy-aspath-20] quit

[DeviceC] route-policy aspath permit node 25

# Apply routing policy aspath to routes from the peer 35.35.35.5.

[DeviceC] bgp 100

[DeviceC-bgp-default] address-family ipv4

[DeviceC-bgp-default-ipv4] peer 35.35.35.5 route-policy aspath import

Verifying the configuration

# Display the BGP routing table on Device A. The output shows that the local preference of routes whose AS_PATH attributes end with AS number 400 changes to 300.

[DeviceA] display bgp routing-table ipv4

Total number of routes: 11

BGP local router ID is 1.1.1.1

Status codes: * - valid, > - best, d - dampened, h - history

s - suppressed, S - stale, i - internal, e – external

a - additional-path

Origin: i - IGP, e - EGP, ? - incomplete

Network NextHop MED LocPrf PrefVal Path/Ogn

* >i 2.2.2.2/32 12.12.12.2 0 100 0 ?

* >i 3.3.3.3/32 13.13.13.3 0 100 0 ?

* >i 4.4.4.4/32 24.24.24.4 0 100 0 200i

* i 35.35.35.5 100 0 300 400

200i

* >i 5.5.5.5/32 35.35.35.5 0 100 0 300i

* i 24.24.24.4 100 0 200 400

300i

* >i 6.6.6.6/32 35.35.35.5 300 0 300 400i

* i 24.24.24.4 100 0 200 400i

* >i 12.12.12.0/24 12.12.12.2 0 100 0 ?

* >i 13.13.13.0/24 13.13.13.3 0 100 0 ?

* >i 24.24.24.0/24 12.12.12.2 0 100 0 ?

* >i 35.35.35.0/24 13.13.13.3 0 100 0 ?

# Verify that packets from Device A to 6.6.6.6 are forwarded by Device D.

[DeviceA] tracert 6.6.6.6

traceroute to 6.6.6.6 (6.6.6.6), 30 hops at most, 52 bytes each packet, press CT

RL_C to break

1 12.12.12.2 (12.12.12.2) 2.417 ms 1.887 ms 1.773 ms

2 35.35.35.5 (35.35.35.5) 4.057 ms 2.293 ms 2.739 ms

3 6.6.6.6 (6.6.6.6) 5.145 ms 4.205 ms 4.402 ms

Configuration files

Device A

interface LoopBack0

ip address 1.1.1.1 255.255.255.255

interface ten-gigabitethernet 3/1/1

port link-mode route

ip address 12.12.12.1 255.255.255.0

interface ten-gigabitethernet 3/1/2

port link-mode route

ip address 13.13.13.1 255.255.255.0

bgp 100

router-id 1.1.1.1

peer 12.12.12.2 as-number 100

peer 13.13.13.3 as-number 100

address-family ipv4 unicast

peer 12.12.12.2 enable

peer 13.13.13.3 enable

Device B

interface LoopBack0

ip address 2.2.2.2 255.255.255.255

interface ten-gigabitethernet 3/1/1

port link-mode route

ip address 12.12.12.2 255.255.255.0

interface ten-gigabitethernet 3/1/2

port link-mode route

ip address 24 24.24.2 255.255.255.0

bgp 100

router-id 2.2.2.2

peer 12.12.12.1 as-number 100

peer 24.24.24.4 as-number 200

address-family ipv4 unicast

import-route direct

peer 12.12.12.1 enable

peer 24.24.24.4 enable

Device C

interface LoopBack0

ip address 3.3.3.3 255.255.255.255

interface ten-gigabitethernet 3/1/1

port link-mode route

ip address 13.13.13.3 255.255.255.0

interface ten-gigabitethernet 3/1/2

port link-mode route

ip address 35.35.35.3 255.255.255.0

bgp 100

router-id 3.3.3.3

peer 13.13.13.1 as-number 100

peer 35.35.35.5 as-number 300

address-family ipv4 unicast

import-route direct

peer 13.13.13.1 enable

peer 35.35.35.5 enable

peer 35.35.35.5 route-policy aspath import

route-policy aspath permit node 20

if-match as-path 1

apply local-preference 300

route-policy aspath permit node 25

ip as-path 1 permit 400$

Device D

interface LoopBack0

ip address 4.4.4.4 255.255.255.255

interface ten-gigabitethernet 3/1/1

port link-mode route

ip address 24.24.24.4 255.255.255.0

interface ten-gigabitethernet 3/1/2

port link-mode route

ip address 46.46.46.4 255.255.255.0

bgp 200

router-id 4.4.4.4

peer 24.24.24.2 as-number 100

peer 46.46.46.6 as-number 400

address-family ipv4 unicast

network 4.4.4.4 255.255.255.255

peer 24.24.24.2 enable

peer 46.46.46.6 enable

Device E

interface LoopBack0

ip address 5.5.5.5 255.255.255.255

interface ten-gigabitethernet 3/1/1

port link-mode route

ip address 35.35.35.5 255.255.255.0

interface ten-gigabitethernet 3/1/2

port link-mode route

ip address 56.56.56.5 255.255.255.0

bgp 300

router-id 5.5.5.5

peer 35.35.35.3 as-number 100

peer 56.56.56.6 as-number 400

address-family ipv4 unicast

network 5.5.5.5 255.255.255.255

peer 35.35.35.3 enable

peer 56.56.56.6 enable

Device F

interface LoopBack0

ip address 6.6.6.6 255.255.255.255

interface ten-gigabitethernet 3/1/1

port link-mode route

ip address 46.46.46.6 255.255.255.0

interface ten-gigabitethernet 3/1/2

port link-mode route

ip address 56.56.56.6 255.255.255.0

bgp 400

router-id 6.6.6.6

peer 46.46.46.4 as-number 200

peer 56.56.56.5 as-number 300

address-family ipv4 unicast

network 6.6.6.6 255.255.255.255

peer 46.46.46.4 enable

peer 56.56.56.5 enable

Example: Configuring route selection based on the MED attribute

Network configuration

As shown in Figure 2, all devices run BGP. EBGP runs between Device A and Device B, and between Device A and Device C. IBGP runs between Device B and Device C.

Configure a routing policy to ensure that traffic from AS 100 to AS 200 is preferentially forwarded by Device C. Before you configure the routing policy, the traffic is preferentially forwarded by Device B.

Figure 2 Network diagram

‌

Analysis

To ensure that the traffic is preferentially forwarded by Device C, configure a routing policy on Device B to change the MED value for the route to Device A. Make sure the MED value is not the default MED value 0.

Procedures

Configuring basic BGP

# Configure an IP address for interface Ten-GigabitEthernet 3/1/1 on Device A.

<DeviceA> system-view

[DeviceA] interface ten-gigabitethernet 3/1/1

[DeviceA-Ten-GigabitEthernet3/1/1] ip address 12.12.12.1 24

[DeviceA-Ten-GigabitEthernet3/1/1] quit

# Configure IP addresses for other interfaces as shown in Figure 2. (Details not shown.)

# On Device A, enable the default BGP instance, set the AS number to 100, and specify 12.12.12.2 and 13.13.13.3 as BGP peers.

[DeviceA] bgp 100

[DeviceA-bgp-default] router-id 1.1.1.1

[DeviceA-bgp-default] peer 12.12.12.2 as-number 200

[DeviceA-bgp-default] peer 13.13.13.3 as-number 200

[DeviceA-bgp-default] address-family ipv4 unicast

[DeviceA-bgp-default-ipv4] peer 12.12.12.2 enable

[DeviceA-bgp-default-ipv4] peer 13.13.13.3 enable

[DeviceA-bgp-default-ipv4] quit

[DeviceA-bgp-default] quit

# On Device B, enable the default BGP instance, set the AS number to 200, and specify 12.12.12.1 and 3.3.3.3 as BGP peers.

[DeviceB] bgp 200

[DeviceB-bgp-default] router-id 2.2.2.2

[DeviceB-bgp-default] peer 12.12.12.1 as-number 100

[DeviceB-bgp-default] peer 3.3.3.3 as-number 200

[DeviceB-bgp-default] peer 3.3.3.3 connect-interface LoopBack0

[DeviceB-bgp-default] address-family ipv4 unicast

[DeviceB-bgp-default-ipv4] peer 12.12.12.1 enable

[DeviceB-bgp-default-ipv4] peer 3.3.3.3 enable

[DeviceB-bgp-default-ipv4] network 23.23.23.0 24

[DeviceB-bgp-default-ipv4] quit

[DeviceB-bgp-default] quit

# Configure a static route to 3.3.3.3/32 on Device B.

[DeviceB] ip route-static 3.3.3.3 32 23.23.23.3

# On Device C, enable the default BGP instance, set the AS number to 200, and specify 13.13.13.1 and 2.2.2.2 as BGP peers.

[DeviceC] bgp 200

[DeviceC-bgp-default] router-id 3.3.3.3

[DeviceC-bgp-default] peer 13.13.13.1 as-number 100

[DeviceC-bgp-default] peer 2.2.2.2 as-number 200

[DeviceC-bgp-default] peer 2.2.2.2 connect-interface LoopBack0

[DeviceC-bgp-default] address-family ipv4 unicast

[DeviceC-bgp-default-ipv4] peer 13.13.13.1 enable

[DeviceC-bgp-default-ipv4] peer 2.2.2.2 enable

[DeviceC-bgp-default-ipv4] network 23.23.23.0 24

[DeviceC-bgp-default-ipv4] quit

[DeviceC-bgp-default] quit

# Configure a static route to 2.2.2.2/32 on Device C.

[DeviceC] ip route-static 2.2.2.2 32 23.23.23.2

# Display the BGP routing table on Device A. The output shows that the route with the next hop 12.12.12.2 becomes the optimal route to the network 23.23.23.0/24.

[DeviceA] display bgp routing-table ipv4

Total number of routes: 2

BGP local router ID is 1.1.1.1

Status codes: * - valid, > - best, d - dampened, h - history

s - suppressed, S - stale, i - internal, e – external

a - additional-path

Origin: i - IGP, e - EGP, ? - incomplete

Network NextHop MED LocPrf PrefVal Path/Ogn

* >e 23.23.23.0/24 12.12.12.2 0 0 200i

* e 13.13.13.3 0 0 200i

Configuring a routing policy

# Create routing policy 10 on Device B and set the cost to 100.

[DeviceB] route-policy 10 permit node 10

[DeviceB-route-policy-10-10] apply cost 100

[DeviceB-route-policy-10-10] quit

# Apply routing policy 10 to routes to the peer 12.12.12.1.

[DeviceB] bgp 200

[DeviceB-bgp-default] address-family ipv4 unicast

[DeviceB-bgp-default-ipv4] peer 12.12.12.1 route-policy 10 export

[DeviceB-bgp-default-ipv4] quit

[DeviceB-bgp-default] quit

Verifying the configuration

# Display the BGP routing table on Device A. The output shows that the MED value for the route with the next hop 12.12.12.2 changes to 100, and the route with the next hop 13.13.13.3 becomes the optimal route.

[DeviceA] display bgp routing-table ipv4

Total number of routes: 2

BGP local router ID is 1.1.1.1

Status codes: * - valid, > - best, d - dampened, h - history

s - suppressed, S - stale, i - internal, e – external

a - additional-path

Origin: i - IGP, e - EGP, ? - incomplete

Network NextHop MED LocPrf PrefVal Path/Ogn

* >e 23.23.23.0/24 13.13.13.3 0 0 200i

* e 12.12.12.2 100 0 200i

Configuration files

Device A

interface LoopBack0

ip address 1.1.1.1 255.255.255.255

interface ten-gigabitethernet 3/1/1

port link-mode route

ip address 12.12.12.1 255.255.255.0

interface ten-gigabitethernet 3/1/2

port link-mode route

ip address 13.13.13.1 255.255.255.0

bgp 100

router-id 1.1.1.1

peer 12.12.12.2 as-number 200

peer 13.13.13.3 as-number 200

address-family ipv4 unicast

peer 12.12.12.2 enable

peer 13.13.13.3 enable

Device B

interface LoopBack0

ip address 2.2.2.2 255.255.255.255

interface ten-gigabitethernet 3/1/1

port link-mode route

ip address 12.12.12.2 255.255.255.0

interface ten-gigabitethernet 3/1/2

port link-mode route

ip address 23.23.23.2 255.255.255.0

bgp 200

router-id 2.2.2.2

peer 3.3.3.3 as-number 200

peer 3.3.3.3 connect-interface LoopBack0

peer 12.12.12.1 as-number 100

address-family ipv4 unicast

network 23.23.23.0 255.255.255.0

peer 3.3.3.3 enable

peer 12.12.12.1 enable

peer 12.12.12.1 route-policy 10 export

route-policy 10 permit node 10

apply cost 100

ip route-static 3.3.3.3 32 23.23.23.3

Device C

interface LoopBack0

ip address 3.3.3.3 255.255.255.255

interface ten-gigabitethernet 3/1/1

port link-mode route

ip address 13.13.13.3 255.255.255.0

interface ten-gigabitethernet 3/1/2

port link-mode route

ip address 23.23.23.3 255.255.255.0

bgp 200

router-id 3.3.3.3

peer 2.2.2.2 as-number 200

peer 2.2.2.2 connect-interface LoopBack0

peer 13.13.13.1 as-number 100

address-family ipv4 unicast

network 23.23.23.0 255.255.255.0

peer 2.2.2.2 enable

peer 13.13.13.1 enable

ip route-static 2.2.2.2 32 23.23.23.2

02-Configuration Examples

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