BGP Tutorial for ISP customers – Configuring BGP

To bring BGP session minimum requires a configuration is really simple.  Just three lines of BGP statement will bring BGP session.
This is kinds of important to know, when you are troubleshooting.  If BGP doesnt come up, just simplify BGP configuration. It is sometimes best troubleshooting steps.

• BGP Tutorial for ISP customers – Do I need BGP?
• BGP Tutorial for ISP customers – Own ASN or borrowing one.
• BGP Tutorial for ISP customers – Enough memory for full routes?
• BGP Tutorial for ISP customers – Controlling outbound traffic.
• BGP Tutorial for ISP customers – Controlling inbound traffic.
• BGP Tutorial for ISP customers – Configuring BGP
• BGP Tutorial for ISP customers – BGP community string from ISP.
• BGP Tutorial for ISP customers – Verifying BGP routes.
• BGP Tutorial for ISP customers – BGP Troubleshooting.

 

 

Basic configruation

router bgp 65535
network z.z.z.0
neighbor y.y.y.y remote-as 65500

Cisco_Router(config)#router bgp 65535 <– your ASN 65535 in this example
Cisco_Router(config-router)#neighbor y.y.y.y remote-as KKKK ß BGP neighbors ASN, y.y.y.y is neighbor IP address
Cisco_Router(config-router)#network z.z.z.0 mask 255.255.255.0 ß BGP route that you want to announce to neighbor

** Do you need to specify BGP version 4 unless one of peer is using different version

 

MD5 configuration

After MD5 setup and establishing BGP, wait until hold time is expired. Somtime MD5 disgest issue would be encounter.

router bgp 65535
network z.z.z.0
neighbor y.y.y.y remote-as 65500
neighbor y.y.y.y password <– MD5 will be encrypted after applied.

Cisco_Router(config)#router bgp 65535 <– your ASN 65535 in this example
Cisco_Router(config-router)#neighbor y.y.y.y remote-as KKKK <– BGP neighbors ASN, y.y.y.y is neighbor IP address
Cisco_Router(config-router)#network z.z.z.0 mask 255.255.255.0 <– BGP route that you want to announce to neighbor
Cisco_Router(config-router)#neighbor y.y.y.y password abcdefg <– MD5 password abcdefg in this case

 

Route-map filtering configuration

Using route-map, you can control in/outbound BGP announcement and apply various attributes

router bgp 65535
network z.z.z.0
neighbor y.y.y.y remote-as 65500
neighbor y.y.y.y route-map ISP-out out

route-map ISP-out permit 10
match ip address 100
set as-path prepend 65535 65535 65535 65535

access-list 100 permit z.z.z.0 0.0.0.255

Cisco_Router(config)#router bgp 65535 <– your ASN 65535 in this example
Cisco_Router(config-router)#neighbor y.y.y.y remote-as KKKK <– BGP neighbors ASN, y.y.y.y is neighbor IP address
Cisco_Router(config-router)#network z.z.z.0 mask 255.255.255.0 <– BGP route that you want to announce to neighbor
Cisco_Router(config-router)#network y.y.y.y route-map ISP-out out <– BGP route-map is applied on outbound

 

BGP Filter-list configuration

It provides different kinds of filtering

router bgp 65535
network z.z.z.0
neighbor y.y.y.y remote-as 65500
neighbor y.y.y.y filter-list 200 in
ip as-path access-list 200 permit _7777$ <– Only allow BGP route on the path ASN started with 7777

Cisco_Router(config)#router bgp 65535 <– your ASN 65535 in this example
Cisco_Router(config-router)#neighbor y.y.y.y remote-as KKKK <– BGP neighbors ASN, y.y.y.y is neighbor IP address
Cisco_Router(config-router)#network z.z.z.0 mask 255.255.255.0 <– BGP route that you want to announce to neighbor
Cisco_Router(config-router)#network y.y.y.y filter-list 200 in <– BGP filter-list is applied on inbound

 

BGP community string configuration

See following BGP series of article