BGP Community String

Support for transit customers

1759:1050 Set local pref 50 (lower than upstream LP)
1759:1100 Set local pref 110 (lower than CIX LP)
1759:1150 Set local pref 150 (lower than primary customer LP)
1759:666 Black hole routing

Prepend x times (x=1,2,3) or do NOT announce (x=0)

1759:100X All direct peers
1759:200x Upstream Provider
1759:300X Cix and private peers
1759:400x CIX
1759:500x Private peers

Following signaling BGP communities are available for FICIX peers:

1759:1110 Set local pref 110

(lower than CIX default local pref)

1759:666 Black hole routing

Applying BGP Community string with sample configuration

1. Get the latest BGP community string from your ISP/upstream provider or check new.CiscoNET.com web site.

2. Pick the best BGP community string for your traffic shaping plan (mainly incoming traffic).
Most of ISPs are providing community string with local preference and AS prepending
option. Cannot tell which one is better than the other. It will depend on your global traffic shaping plan.

3. Follow the below commands ( Cisco only )

The below Sample configuration will tag the 10.0.0.0/24 route with [ISP AS]:120 or [ISP AS]:3 and will not tag any other routes.

router#config t
router(config)#ip bgp-community new-format
router(config)#access-list 10 permit 10.0.0.0 0.0.0.255
router(config)#access-list 10 deny any

router(config)#route-map [to-ISP] permit 10
router(config-route-map)#match ip address 10
router(config-route-map)#set community [ISP AS]:120 <---- using Local Preference

router(config-route-map)#set community [ISP AS]:3 <------- using AS prepending
router(config-route-map)#route-map [to-ISP] permit 20
router(config-route-map)#exit

router(config)#router bgp [xxxx] <------------------------------- xxxx = customer's ASN
router(config-router)#neighbor x.x.x.x send-community
router(config-router)#neighbor x.x.x.x route-map [to-ISP] out
router(config-router)#exit
router(config)#exit
router#copy running-config startup-config

4. And then, go to www.CiscoNET.com and pick one of route server on the map to see your announcement. If you are using AS prepending option, you will see your AS prepends on route servers. Sometime you might not see your route with particular ISP path.
In most of case it might not be any routing problem, just the route path was dropped at somewhere by BGP best path selection scheme. Try Oregon route server, if you can see your route. The Oregon route server is providing many possible and available paths between BGP speakers and neighbors.
If you don't see your route on there? check other route servers and also check your
BGP configuration. You might need to contact your upstream provider to check what they are learning BGP route from you.

Add as favourites (15) | Views: 157 | E-mail

Be first to comment this article

Write Comment
Please keep the topic of messages relevant to the subject of the article. Personal verbal attacks will be deleted. Please don't use comments to plug your web site. Such material will be removed. Just ensure to Refresh your browser for a new security code to be displayed prior to clicking on the 'Send' button. Keep in mind that the above process only applies if you simply entered the wrong security code.
Name:
E-mail
Title:
BBCode:
Comment:
Code:*