BGP Community String for Global Crossing AS3549

   March 27, 2007  Leave a comment

Attention

This BGP Community string information might be outdated. Please contact Global Crossing AS3549 to get more recent one. This BGP communites is ONLY for the customer who has BGP with Global Crossing AS3549. www.ipbalance.com is not maintaining this BGP Community string.

 

Control of GBLX BGP Community Attributes

GBLX allows customers to modify various attributes of their announced prefixes within the GBLX network. Customers can alter the local preference of their prefixes, thus changing whether a prefix is chosen as the preferred route. However, many external influences can affect whether any given prefix is chosen as the best route. If you are multihomed and GBLX hears your route(s) from another provider and you alter your local preference to a value lower than the peer’s value, the peer learned prefix will be chosen.

 

In order for you to appropriately manipulate your local preference values, the following is the standard policy applied for GBLX network customers and peers:

 

Customers:
Local Preference : 300
Metric Policy : Accept customers’ metrics

 

Peers:
Local Preference : 200
Metric Policy : Do not accept peers’ metrics.

 

BGP Community String

Action
3549:100 set local preference 100
3549:200

set local preference 200

3549:275

set local preference 275
3549:300 set local preference 300
3549:350 set local preference 350

 

 

Control of Route Propagation

GBLX provides the customer limited control over how their prefixes are propagated to various network peers. This is accomplished using as-path prepending at the GBLX-Peer border. The following BGP communities may be sent to prepend customer announced prefixes:

 

BGP Community String

Action
3549:600 Deny inter-continental export of tagged prefix [iBGP].
3549:666 Deny inter-as export of tagged prefix
(deny to peers, send to customers) [eBGP].

 

For a limited subset of GBLX peering connections, more granular control of announcements is provided. If GBLX sees a BGP community matching 3549:8…, routing announcements sent to the following listed ASNs will be modified according to these rules :

 

ASN

Peer

No Export

Prepend +1

Prepend +2

Prepend +3

174 Cogent 8280 8281 8282 8283
209 Qwest 8010 8011 8012 8013
577 Bellnexxia 8090 8091 8092 8093
701 MCI 8030 8031 8032 8033
1239 Sprint 8060 8061 8062 8063
1257 Tele2 8110 8111 8112 8113
1299 TeliaSonera 8250 8251 8252 8253
1668 AOL 8070 8071 8072 8073
2497 JPNIC 8080 8081 8082 8083
2516 KDDI 8100 8101 8102 8103
2828 XO 8260 8261 8262 8263
2914 NTT Verio 8120 8121 8122 8123
3257 Tiscali 8240 8241 8242 8243
3300 InfoNet Europe 8130 8131 8132 8133
3303 Swisscom 8140 8141 8142 8143
3320 DTAG 8150 8151 8152 8153
3356 Level 3 8160 8161 8162 8163
3561 Savvis 8170 8171 8172 8173
4134 ChinaNet 8230 8231 8232 8233
5511 OpenTransit 8190 8191 8192 8193
6453 Teleglobe 8210 8211 8212 8213
6461 AboveNet 8200 8201 8202 8203
6762 Seabone (TI) 8050 8051 8052 8053
6830 UPC/Chello 8180 8181 8182 8183
7018 AT&T (US) 8220 8221 8222 8223
7473 Singtel 8040 8041 8042 8043
7911 Wilcom 8020 8021 8022 8023
12956 Telefonica 8270 8271 8272 8273

 

This example below illustrates the use of these BGP communities.

A customer with ASN 65535 sends GBLX a route tagged with BGP communities "3549:8011 3549:8033 3549:8190"

When that route is reannounced across GBLX peering connections:

    • Qwest (AS 209) will see an AS path of: "3549 3549 65535"
    • MCI (AS 701) will see a path of: "3549 3549 3549 3549 65535"
    • OpenTransit (AS 5511) will not see the route at all
    • All other peers will see: "3549 65535"

 

 

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 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.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.

 

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