BGP Attribute Session Basic Configuration Network Topology Overview
■ Content
1 eBGP and iBGP Configuration
2 Verify Results of Pre-configuration on RT4
3 AS-Path Attribute Configuration
4 Verify after network command line on RT4
✓ RT4 receives 1.1.1.1/32 route from RT2 and RT3
but in this session RT4 only receive 1.1.1.1/32
route from RT3
Step
4 AS-Path Attribute
❖ BGP Attributes Table
Priority Attribute
1 ✓ Weight
2 ✓ Local Preference
3 ✓ Originate
4 As Path Length
5 ✓ Origin Code
6 MED
7 eBGP path over iBGP path
8 Shortest IGP path to BGP next hop
9 Oldest Path
10 Router ID
11 Neighbor IP Address
https://networklessons.com/bgp/bgp-attributes-and-path-selection
❖ IP address Assign
Device Name IP Address Subnet Mask
RT1 and RT2 10.10.12.1 and 10.10.12.2 255.255.255.252
RT1 and RT3 10.10.13.1 and 10.10.13.2 255.255.255.252
RT2 and RT4 10.10.24.1 and 10.10.24.2 255.255.255.252
RT3 and RT4 10.10.34.1 and 10.10.34.2 255.255.255.252
RT1 Loopback 0 1.1.1.1 255.255.255.255
RT2 Loopback 0 2.2.2.2 255.255.255.255
RT3 Loopback 0 3.3.3.3 255.255.255.255
RT4 Loopback 0 4.4.4.4 255.255.255.255
1 eBGP and iBGP Configuration
RT1 RT2 RT3 RT4
interface Loopback0 interface Loopback0 interface Loopback0 interface Loopback0
ip address 1.1.1.1 255.255.255.255 ip address 2.2.2.2 255.255.255.255 ip address 3.3.3.3 255.255.255.255 ip address 4.4.4.4 255.255.255.255
! ! ! !
interface Ethernet0/0 interface Ethernet0/0 interface Ethernet0/0 interface Ethernet0/0
description RT1_TO_RT2 description RT2_TO_RT1 description RT3_TO_RT1 description RT4_TO_RT3
ip address 10.10.12.1 255.255.255.252 ip address 10.10.12.2 255.255.255.252 ip address 10.10.34.1 255.255.255.252 ip address 10.10.34.2 255.255.255.252
! ! ! !
interface Ethernet0/1 interface Ethernet0/1 interface Ethernet0/1 interface Ethernet0/1
description RT1_TO_RT3 description RT2_TO_RT4 description RT3_TO_RT4 description RT4_TO_RT2
ip address 10.10.13.1 255.255.255.252 ip address 10.10.24.1 255.255.255.252 ip address 10.10.13.2 255.255.255.252 ip address 10.10.24.2 255.255.255.252
! ! ! !
interface Ethernet0/2 interface Ethernet0/2 interface Ethernet0/2 interface Ethernet0/2
no ip address no ip address no ip address no ip address
shutdown shutdown shutdown shutdown
! ! ! !
interface Ethernet0/3 interface Ethernet0/3 interface Ethernet0/3 interface Ethernet0/3
no ip address no ip address no ip address no ip address
shutdown shutdown shutdown shutdown
! ! ! !
router bgp 100 router bgp 400 router bgp 400 router bgp 400
bgp log-neighbor-changes bgp log-neighbor-changes bgp log-neighbor-changes bgp log-neighbor-changes
network 1.1.1.1 mask 255.255.255.255 network 2.2.2.2 mask 255.255.255.255 network 3.3.3.3 mask 255.255.255.255 network 4.4.4.4 mask 255.255.255.255
neighbor 10.10.12.2 remote-as 400 network 10.10.12.0 mask 255.255.255.252 network 10.10.13.0 mask 255.255.255.252 network 10.10.24.0 mask 255.255.255.252
neighbor 10.10.13.2 remote-as 400 network 10.10.24.0 mask 255.255.255.252 network 10.10.34.0 mask 255.255.255.252 network 10.10.34.0 mask 255.255.255.252
neighbor 10.10.12.1 remote-as 100 neighbor 10.10.13.1 remote-as 100 neighbor 10.10.24.1 remote-as 400
neighbor 10.10.24.2 remote-as 400 neighbor 10.10.34.2 remote-as 400 neighbor 10.10.34.1 remote-as 400
neighbor 10.10.24.2 next-hop-self neighbor 10.10.34.2 next-hop-self
2 Verify Results of Pre-configuration on RT4
RT4
❖ Verify that RT4 chosen 1.1.1.1/32 route from RT2
❖ It showing the ( *> ) * Valid and > is Best route
❖ IGP ( Using the network command, it’s showing up as i )
❖ RT4 receives 1.1.1.1/32 route from RT2 and RT3
❖ RT4 Chosen RT2, because of RT2 Router ID is 2.2.2.2
❖ AS-Path 100 i (*** not using AS-Path config *** )
❖ Check RT2 and RT3 BGP Table
❖ (RT2 Priority because of RT2’s Router ID is 2.2.2.2)
RT2
❖ Why chosen RT2 ???
Weight
Local Preference
Originate
As Path Length
Origin Code
MED
eBGP path over iBGP path
Shortest IGP path to BGP next hop
Oldest Path RT3
Router ID = Different
Neighbor IP Address
RT4
❖ Verify that RT4 chosen 1.1.1.1/32 route from RT2 /s 10.10.24.1
3 AS-Path Attribute Configuration , This session RT3 is Priority ❖ Why chosen RT3 ???
Weight = Check the same go to next step
RT2
Local Preference = Check the same go to next step
route-map AS-PATH permit 100
set as-path prepend 100 100 100 ❖ Show ip bgp Originate = Change the network command (Same)
! ❖ Show ip bgp summary As Path Length = Using the AS-Path Prepend
router bgp 400 ❖ Clear ip bgp * soft
neighbor 10.10.12.1 remote-as 400 Origin Code
neighbor 10.10.12.1 route-map AS-PATH in MED
eBGP path over iBGP path
4 Verify after AS-Path Prepend configuration on RT4 Shortest IGP path to BGP next hop
Oldest Path
Router ID
Neighbor IP Address
❖ RT4 receives 1.1.1.1/32 route from RT2 and RT3
❖ RT4 Chosen RT3, because of Shortest AS Path, 100 i
❖ AS-Path has become 100 100 100 100 i
RT4
❖ Verify that RT4 chosen 1.1.1.1/32 route from RT3 /s 10.10.34.1
• Thank You for Reading
• Thank you for taking the time to go through this guide on
BGP Attribute Session. I hope it provides valuable insights
and practical knowledge for your network configurations.
• If you have any questions, feedback, or would like to discuss
further, feel free to reach out. Let's connect and continue
learning together!
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