BGP Community String for XO AS2828

   April 3, 2007  Leave a comment

Attention

This BGP Community string information might be outdated. Please contact XO AS2828 to get more recent one. This BGP communites is ONLY for the customer who has BGP with XO AS2828. ipbalance.com is not maintaining this BGP Community string.

XO BGP Communities Controls

Local Preference BGP Community String
The general XO routing policy is to prefer our customer’s BGP and static routes over "external"
(non-customer) BGP routes.
For our BGP customers, XO has implemented a powerful, flexible system whereby we allow our customers to control – via predefined BGP communities – the XO treatment of their announcements. These BGP communities control XO local-preference (local-pref) of customer -announced routes within our network. The most powerful attribute is local-preference.
In BGP, the higher the local-pref, the more preferred the route on the network. This affects XO backbone route selection only, and not the route selection made by XO peers and customers, because localpreference is non-transitive. This means it does not get passed beyond the XO network. The customer has a range of six local-preferences to which they can set their routes.
The following table details the local-prefs, including the actual value, the BGP community accepted from the customer to set the local-pref, and a description of what that local-pref will do in the network.

 

BGP Community String Local Prep Description
2828:1507 70 Lower (less preferred) than all
other routes on network, incl all
public & private peer routes
2828:1508 80 Same as public and private
peers.
2828:1509 90  
none 100 Default for all customer routes,
BGP and static
2828:1510 100 Explicitly set customer BGP
announcements to 100
2828:1511 110 Higher (more preferred) than all
default customer BGP and static
routes
2828:1512 120 Highest (most preferred) localpref
that a customer can specify

 

AS-Path Controls

The next attribute that customers can use to control their routing is via AS path length.
The most common use of AS-path prepending is in a direct peering route-map on the customer end where they can prepend their own AS to their routes as they announce the routes to AS2828. XO also accepts BGP communities that prepend AS 2828 either one time or three times to the route as it leaves the 2828 network.
Currently, there are three general groups on which the customer can set 2828 prepends:

 

BGP Communities that Change Customer Announcements to Certain Peers atAS2828 Border
Provider
Name or
Group		 "Don’t
Advertise to"
BGP Community		 "Prepend
Once"
BGP Community		 "Prepend
Twice"
BGP Community		 “Prepend
Thrice”
BGP Community
All
Peers		 2828:1000 2828:1100
 2828:1200
 2828:1300
Sprint 2828:1003 2828:1103
 2828:1203
 2828:1303
Cable &
Wireless		 2828:1004 2828:1104 2828:1204
 2828:1304
Verizon 2828:1006 2828:1106
 2828:1206
 2828:1306
Level3 2828:1007 2828:1107
 2828:1207
 2828:1307
ATT 2828:1008 2828:1108
 2828:1208
 2828:1308

 

Origin Attribute
Another standard option for customers to control XO treatment of their advertisements involves the use of the origin attribute.
XO does not alter origin code on routes customers send us. Routes set with the IGP origin code are more preferred than routes tagged with the origin EGP code, which are more preferred than origin-Incomplete routes.


DoS Discard Community
XO provides a mechanism allowing customers to trigger the XO backbone to discard all traffic entering the XO network from external sources destined for any routes specifically announced by a BGP customer with a special BGP community.


XO customers may announce this route to XO to mitigate the over utilization of their uplink or general harm caused by such an attack until they open a ticket (if required) and XO technicians help stop the attack.

 

Other Accepted BGP Communities
BGP Community String Description
2828:1650 Used to blackhole traffic
no-export/no-advertise Don’t announce outside of XO

 

MED Controls

Another standard option for customers to control XO treatment of their advertisements involves the use of the MED attribute. The lower the MED attribute set on a route, the more preferred the route. XO currently accepts MED from its customers.
For more details on (Cisco) BGP path selection and attributes, see Cisco’s Web site.

 

Sample Customer Configurations
The following configurations are samples, provided for educational purposes only.
Customers managing their own CPE, running BGP to XO Communications, should understand the abilities of the protocol, and manage their router based on their own needs. Inbound controls could be stricter and many other variations could place different configuration requirements.
The examples below show simple and complex configurations, but they could become more complex depending on the customer’s needs.
For further guidance, see the Cisco Web site.

 

 

Applying BGP Community string with sample configuration

1. Get the latest BGP community string from your ISP/upstream provider or check www.ShowipBGP.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

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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