• 1273:32000 – Do not announce to MCI Europe (AS702)
• 1273:31752 – Prepend twice to Reach (AS4637)
• 1273:39963 – Prepend three times to Level 3 Upstream connection (AS3356)

C&W Blackhole BGP Community Attribute Values (1273:666)

C&W local preference alteration BGP communities

• The local-preference hierarchy within C&W AS1273 is as follows
  

  Value	Effect
  100	Customers (BGP and injected static)
  90	Backup customer connections
  80	Peers
  75	Transit/Upstream Providers
  70	Last resort customer connections

• The following BGP communities can be sent to influence the local-preference of a customer route
  

  BGP Community String	Effect
  1273:90	Sets local preference value within AS1273 to 90
  1273:80	Sets local preference value within AS1273 to 80
  1273:70	Sets local preference value within AS1273 to 70
  1273:no-export	Prevents this route from being announce to any AS1273 EBGP peer
  1273:no-advertise	Prevents this route from being announced to any AS1273 EBGP or IBGP peer

Applying BGP Community string with sample configuration

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

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.routeserver.org 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.