BGP Community String:
|
Standard Community
|
Do Not Advertise
|
One
Prepend
|
Two Prepends
|
Three Prepends
|
All
|
16030:100 | 16030:1000 | 16030:1001 | 16030:1002 | 16030:1003 |
All Transits | 16030:101 | 16030:1010 | 16030:1011 | 16030:1012 | 16030:1013 |
All Peers | 16030:102 | 16030:1020 | 16030:1021 | 16030:1022 | 16030:1023 |
All Customers | 16030:103 | 16030:1030 | 16030:1031 | 16030:1032 | 16030:1033 |
Catnix (Barcelona) | 16030:104 | 16030:1040 | 16030:1041 | 16030:1042 | 16030:1043 |
SwissIX (Zurich) | 16030:105 | 16030:1050 | 16030:1051 | 16030:1052 | 16030:1053 |
NYIIX (New York) | 16030:106 | 16030:1060 | 16030:1061 | 16030:1062 | 16030:1063 |
Ams-IX (Amsterdam) | 16030:107 | 16030:1070 | 16030:1071 | 16030:1072 | 16030:1073 |
Linx (London) | 16030:108 | 16030:1080 | 16030:1081< | 16030:1082 | 16030:1083 |
Route maps examples:
This example shows how to deny all your advertisement to All Transits:
route-map altecom-out
permit 10
set community 16030:1010
This example shows how to prepend advertisements to Ams-IX two times, and deny advertisements to All Transits:
route-map altecom-out
permit 10
set community 16030:1010 16030:1072
Applying BGP Community string with sample configuration
1. Get the latest BGP community string from your ISP/upstream provider or check www.ShowipBGP.com.
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 16030:1032 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-AS16030 permit 10
router(config-route-map)#match ip address 10
router(config-route-map)#set community 16030:1032 <—— using Local Preference
router(config-route-map)#route-map to-AS16030 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-AS16030 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.