1. Overview/Introduction
This document is meant to concisely describe the signalling options that Deutsche Telekom’s AS3320 makes available to customer networks supported by BGP routing (transit service products). The intended audience is a customer’s network administrator who is familiar with BGP and general public Internet routing techniques as well as how to configure and control their routers. This version of the document describes the options as defined for the initial roll out of the advanced routing policy definitions (implemented using the TROPOS configuration generator) identified as TSD3320 v1.0 targetted for January 17th 2005.
2. Customer Requests for Special Handling of Routes (by AS3320)
based routing can signal requests for specific treatment of their routes by setting BGP
communities as defined in this chapter.
2.1 Well known BGP communities
The official list of defined well known BGP communities is maintained by IANA, and made
available at http://www.iana.org/assignments/bgp-well-known-communities .
The long standing 3 well known BGP communities (NO_EXPORT, NO_ADVERTISE,
NO_EXPORT_SUBCONFED) are internally used within AS3320.
AS3320 does NOT accept routes with these BGP communities from neighbor AS (to avoid various inconsistencies within AS3320 and potentially with route announcements to customers). The recently defined well known BGP Community NOPEER however is supported by AS3320; customer networks can use this BGP community to restrict propagation of their route. Use of this BGP community as described in the defining RFC is encouraged.
2.1.1 No export
mnemonic: wkcNoExport
aka: NO_EXPORT (IANA)
no-export (IOS)
value: 65535:65281 0xFFFFFF01
AS3320 does not accept routes marked with this BGP community over eBGP.
2.1.2 No advertise
mnemonic: wkcNoAdvertise
aka: NO_ADVERTISE (IANA)
no-advertise (IOS)
value: 65535:65282 0xFFFFFF02
AS3320 does not accept routes marked with this BGP community over eBGP.
2.1.3 No export subconfed
mnemonic: wkcLocalAS
aka: NO_EXPORT_SUBCONFED (IANA)
local-AS (IOS)
value: 65535:65283 0xFFFFFF03
AS3320 does not accept routes marked with this BGP community over eBGP.
2.1.4 NOPEER
mnemonic: wkcNOPEER
aka: NOPEER (IANA)
value: 65535:65284 0xFFFFFF04
Defined by RFC 3765 (G. Huston, "NOPEER BGP community for BGP route scope control")
AS3320 supports this BGP community.
2.2 Controlling Route Priority within AS3320 (Local_Preference)
Currently AS3320 assigns a standard local preference value of 100. It is expected that policies regarding internal route priority will be refined. There are options to statically set lower or higher priorities. Requesting higher priorities requires authorization.
With TDS3320 v1.0 configuration of a LocalPref options has to be requested explicitly to
enable these request BGP communities for a customer AS. (In the next release we will enable at least reqLPrefStd100 and reqLPrefLow50 by default.)
2.2.1 Standard Priority (100)
mnemonic: reqLPrefStd100
value: 65001:100
Can be used to explicitly request standard routing priority within AS3320; e.g. to override
higher priority set that might be applicable for whatever reason and configuration option.
2.2.2 Low Priority (50)
mnemonic: reqLPrefLow50
value: 65001:50
This request will be honored if any Local Preference option is configured for the customer
connection.
2.2.3 High Priority (150)
mnemonic: reqLPrefHigh150
value: 65001:150
Raising priority will be honored only for authorized routes.
2.3 Requesting Blackholing Service
mnemonic: reqBlackhole
value: 65000:0
Requires authorization from holder of address space; the set of routes accepted for
blackholing in general will be different from the routes accepted for regular routing.
Blackholing routes will be more specific routes covering address space supported for regular routing.
3. Influencing Route Propagation to Other AS
3.1 Restrict Route Propagation
Customer networks may use these BGP communities to restrict propagation of their routes from AS3320 to it’s peers (including upstream); please consider using the well known BGP community NOPEER where appropriate. The restriction can be defined by explicitly naming peer AS to be excluded, or by excluding certain classes of peer networks.
3.1.1 by peer AS
mnemonic: reqDontPropagateAS[:as]
value: 65010:xxx for AS numbers 0 < xxx < 64512
3.1.2 by peer class
mnemonic: reqDontPropagateClass[:class]
value: 65010:6500x
subvalues: 65010:65001 peer
65010:65002 upstream
65010:65003 peer and upstream
65010:65007 peer and upstream
3.2 Announce with AS Path Prepending
AS path prepending is a common way of making routes less attractive (as AS path length is usually one of the BGP path selection criteria). Customer networks may use these
BGP communities to selectively request from AS3320 insertion of extra copies of the AS number 3320 when propagating their routes to any of it’s neighbors.
Currently extension of the AS path can be requested by one or two extra AS numbers
(resulting in AS paths seen by neighbor ASs with two or three times 3320).
The path prepending can be requested for explicitly named neighbor ASs or by certain classes of neighbor networks.
3.2.1 AS path prepending per peer AS for AS numbers 0 < xxx < 64512
mnemonic: req2ASprependAS:xxx
value: 65012:xxx
mnemonic: req3ASprependAS:xxx
value: 65013:xxx
3.2.2 AS path prepending per peer class
mnemonic: req2ASprependClass[:class]
value: 65012:xxx
mnemonic: req3ASprependClass[:class]
value: 65013:xxx
subvalues: (for n= 2,3 number of requested occurances of 3320 in path)
6501n:65001 peer
6501n:65002 upstream
6501n:65004 customer
6501n:65003 peer and upstream
6501n:65005 customers and peers
6501n:65006 customers and upstream
6501n:65007 all neighbors
4. Route classification
Customer networks connected to Deutsche Telekom’s AS3320 Internet backbone with BGP
based routing will receive routes with additional classification signalled by BGP community
attributes as defined in this chapter.
4.1 Class of Peer (BGP neighbor injecting the route into AS3320)
4.1.1 Customer network
mnemonic: markNetCustomer
value: 3320:9010
4.1.2 Peer network
mnemonic: markNetPeer
value: 3320:9020
4.2 Country of Import
mnemonic: markCountryImport[:CC]
value: 3320:1ccc with "ccc" 3 decimal digits from the ISO 3166 country codes
subvalues: (with the commonly known 2 letter ISO 3166 country codes)
(please see Appendix A)
CC 3320:1ccc country name
e.g. DE 3320:1276 Germany
4.3 Region of Import
mnemonic: markRegion:2rrr (with rrr 3 decimal digits)
value: 3320:2rrr
subvalues: 3320:2010 Europe
3320:2020 North America
3320:2030 Pacific Rim
5. Options to be explicitly requested/configured
(more details to follow in future versions of this document)
5.1 MD5 protection of eBGP sessions
In general AS3320 expects to negotiate a MD5 key for each neighbor AS to protect all eBGP sessions; AS3320 will propose a MD5 key in each case.
5.2 Announcement of a default route
5.3 Authorization for High Priority (Local Pref)
5.4 Authorization for Blackholing
5.5 Squashing MED
AS3320 accepts and honors by default MED announced by customer networks.
6. Miscellaneous …
Other functions and topics that will be addressed in future versions of this document (or
additional documents) include:
– use of multi-hop eBGP for load-sharing over multiple parallel circuits between a
single pair of border gateways (and in general)
– maximum-prefix limit
– IRR based automatic route filter generation
– authorization requirements and schemes
7. General Information
We are conservative in the set of functions offered; some refinements are likely to follow
early 2005 – including the handling of configuration requests, network data, and authorization.
Future releases certainly will provide significantly enhanced policies and a richer set of
signalling functions.
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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