Time Warner Telecom AS4323 BGP Community String

Local Preference

BGP Community String	Description
4323:80	Set Local Preference in AS4323 to 80
4323:100	Set Local Preference in AS4323 to 100
4323:120	Set Local Preference in AS4323 to 120
4323:187	Blackhole BGP Community — Used only for /32 hosts
4323:555	Advertise to External Peers and Backbone Customers
4323:666	Keep with in TWTC backbone

AS prepend

BGP Community String	Description
4323:1	Prepend AS4323 once
4323:2	Prepend AS4323 twice
4323:3	Prepend AS4323 three times

Network Operations E-mail: [email protected]This e-mail address is being protected from spam bots, you need JavaScript enabled to view it
Network Operations Phone: 800-898-6473 (24/7)
Network Operations Phone (International): 1-303-542-6381 (24/7)
Peering E-mail: [email protected]This e-mail address is being protected from spam bots, you need JavaScript enabled to view it

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 BGP 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

or

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..