AS8681 – JT : BGP Communities

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Policy Description

This document describes two aspects of BGP network control that can be used to form policy decisions throughout the JT Network.

Please note that this policy may not yet be in effect across the whole of AS8681.

It has a number of purposes:

  • To allow JT networks and its’ customers to use communities in order to control how prefixes are handled within the network when announcing to external parties.
  • To provide a coherent and conformant policy on BGP prefix management within the network.
  • To allow JT to increase the efficiency of its’ use of external links.

It is divided into the following sections:

  • Description of communities
  • The use of communities in the JT network (both for classification and for control)


The notation used to represent community values splits the 32-bit attribute into two 16-bit decimal numbers seperated by a single colon `:’. Conventionally, the left-hand value is an AS number and the other is site defined.

There are some predefined community values that are common to all AS’s. Refer to RFC1997 and RFC1998 for more details on Communities.

Use of communities in the JT Network

There are two uses for communities in the JT network: classification of prefixes and control of prefixes.

Only JT itself classifies prefixes as they enter the network at its’ borders. Customers and peers should not do so (and such communities will be filtered at the JT border). These attributes can be used by multihomed downstreams to weight traffic in order to distribute it according to local administrative policies. Prefixes are classified according to geographic entry point, class of prefix (Transit, Public Peering, Private Peering) and which entity of each class (Specific Transit provider, Public Peering point etc).

Prefix control allows the path-extension or filtering entirely of customer prefixes where they are announced at the borders of Jersey Telecoms’ network. Only class of network (Transit, Public Peering, Private Peering) and/or class entity (Specific Transit provider, specific Public Peering point etc) can be targeted.

As a matter of policy, the AS number used for all community strings is AS8681. This allows for consistency across the network.

There are five classes of communities, identified by the number of digits in the right-hand side:

1 digit prefix classification by distribution range
2 digits local preference control and blackholing
3 digits prefix classification by peer or IXP from which it was received
4 digits outgoing announcement control
5 digits prefix classification by location at which it was received

In addition to the communities listed below, the well-known communities (local-AS, no-advertise and no-export) are recognised and can be used (in fact, they’re handled automatically by the routers).

One-digit communities

These communities are set by JT upon entry on the network. They indicate the type of prefix and how it should be distributed. The following communities are used:

8681:1 AS8681 Internal Routes These are locally originated internal-only routes which aren’t announced to any peers.
8681:2 AS8681 Supernets These are Jersey Telecom’s own supernet routes. Unless specifically supressed by other means, this prefix will be announced everywhere, including upstreams and peers. This is announced to transit, peering and customers.
8681:3 Customer Originated Routes These are Jersey Telecom’s BGP customer routes. Unless specifically supressed by other means, this prefix will be announced everywhere, including upstreams and peers. This is announced to transit, peering and customers.
8681:4 Peer Originated Routes This is a prefix received from a private or public IXP peer. This is announced to customers.
8681:5 Transit Originated Routes Originated Network This is a prefix recieved from a transit provider. This is announced to customers.
8681:8 DDoS Mitigated Prefixes Prefixes with this community are forwarded to the mitigation platform.
8681:9 Blackholed Prefixes Prefixes with this community are installed in the forwarding table with a “discard” next hop, i.e. packets with the appropriate destination are discarded instead of forwarded.

Two-digit communities

Customers can set two-digit communities to control which local preference prefixes receive. A two digit community may also be used to enable network-wide blackholing of the announced prefix.

Community       Pref
                 50     Last Resort Transit
                 75     Transit
                100     Peering
8681:10         110     Depreferred DSL Routes
8681:13         130     Depreferred Customer Routes / Default for DSL Routes
8681:15         150     Default for Customer Routes
8681:17         170     Preferred Customer Route
                200     Default for JT-originated Routes

8681:99                 Blackhole - All traffic to this prefix will be 
                        blackholed at JT's border

Three-digit communities

Prefixes coming from peers and transit will be tagged with three-digit community values, e.g. a prefix received at DECIX will be tagged with 8681:641. Only the most specific community is added, e.g. a route from DECIX will not have 8681:640 set. Additionally prefixes from peers will be tagged with a 4xx community based on speed of the interconnection.

Community       Entry point
8681:10x        Internal Routes
8681:101        Redistributed Connected Routes
8681:102        Redistributed Static Routes
8681:103        Private-AS BGP Routes

8681:11x        Internal DSL Routes
8681:111        Redistributed ADSL Connected Routes
8681:112        Redistributed ADSL Static Routes
8681:113        Private-AS BGP ADSL Routes

8681:4xx        Special Markings
8681:410        From a Low capacity IXP (10Mbps)
8681:411        From a Medium capacity IXP (100Mbps)
8681:411        From a High capacity IXP (1Gbps)

8681:5xx        External Transit                       ***
8681:520        Level(3)                               ***
8681:530        Level(3) Paris		               ***
8681:540        AboveNet                               ***
8681:550        Cogent                                 ***
8681:560        SURE PEERING                           ***
8681:570        COGENT PARIS                           ***

8681:591        Hurricane Electric   (IPv6)            ***
8681:592        Tele2                (IPv6)            ***

8681:6xx	From an IXP / NAP                      ***

8681:61x	From UK IXPs                           ***
8681:611	From LINX                              ***
8681:612	From LoNAP

8681:62x	From FR IXPs
8681:621	From PaNAP
8681:622	From FreeIX
8681:623	From SFIX

8681:63x	From NL IXPs
8681:631	From AMS-IX
8681:632        From NL-IX

8681:64x	From DE IXPs
8681:641	From DE-CIX

8681:7xx	From a Private Peer

8681:71x	From a UK private peering

8681:800	Tunneled IPv6 Routes                   ***
8681:801	Tunneled IPv6 Peer                     ***
8681:802	Tunneled IPv6 Customer                 ***

8681:999	Invalid communities recieved

Four-digit communities

Customers can set four-digit communities to control where prefixes are announced. The three-digit communities are used as a base for this and prefixed by 1, 2, 3 or 9 to control prepending of the customer’s prefix on announcement to peers or transits on the specified location.

8681:1xxx Prepend announcement with “8681” on its AS-path
8681:2xxx Prepend announcement with “8681 8681”
8681:3xxx Prepend announcement with “8681 8681 8681”
8681:8xxx Do not prepend (such as when prepend is default)
8681:9xxx Filter announcement, i.e. don’t announce

For example, setting the community 8681:9611 will have the effect that the network on which it is set will not be announced to LINX, whereas setting 8681:9400 will have the effect that the network on which it is set will not be announced to any low-speed IXP or private peer.

These communities may not be implemented in the whole network. When used, it should be verified that the specific community is honored. Otherwise you can request that it is implemented.

For a wider range, the “x” in the list of entry points can be replaced by “0”. So for example “8681:2610” will result in a prepend of length two on all IXPs in the UK, and “8681:2500” has the effect of prepending 8681 to all transits.

Five-digit communities

Every prefix has a five-digit community set which tells on which location it was received. This community has the following format:


where <cc> usually is the country code with possible additions or modification, and <loc> is a number for each of the POPs/locations in the country.

Community       Entry point
8681:1xxxx      Channel Islands

8681:101xx      Jersey 
8681:10101      Central Exchange	
8681:10102      Trinity Gardens	
8681:10103      North Exchange
8681:10104      South Exchange	
8681:10105      East Exchange		
8681:10106      West Exchange		
8681:10107      Five Oaks/TEC		
8681:10108      TEC Colo		
8681:10109      East Colo		
8681:10110      Central Colo		
8681:10111      No.1 The Forum		
8681:10112      No.2 The Forum		
8681:10113      Channel House	
8681:10114      Queen Street Shop	
8681:10115      Rue des Pres		
8681:10116      Hue Court SDR		
8681:10117      Jardin du Soleil SDR	
8681:10118      Waterfront SDR		
8681:10119      Snow Hill SDR		
8681:10120      Fort Regent SDR
8681:10121      Sandybrook SDR		
8681:10122      Hodge Nurseries SDR	
8681:10123      La Chasse SDR		
8681:10124      Trinity SDR		
8681:10125      St. Martin.s SDR	
8681:10126      Mont Mado Store
8681:10127      Victoria Tower

8681:102xx      Guernsey     
8681:10201      St Georges (POP1)
8681:10202      Broadcasting House (POP2)
8681:10203      ITEX Braye Road
8681:10204      ITEX Gibauderie
8681:10205      First Tower Lane
8681:10206      St Georges Hall
8681:10207	Pitronnerie
8681:10208	St Martins
8681:10209	Castel
8681:10210	Alderney

8681:2xxxx      Europe

8681:231xx      NL
8681:13100      NL Originated Supernets

8681:233xx      FR
8681:23300      FR Originated Supernets
8681:23301      FT Aubervilliers

8681:244xx      UK
8681:24400      UK Originated Supernets
8681:24401      Telehouse North
8681:24402      Telehouse East
8681:24403      Telecity Powergate
8681:24404      Telecity Harbour Exchange

8681:249xx      DE
8681:24900      DE Originated Supernets
8681:30000      North America

8681:301xx      USA
8681:30100      USA Originated Supernets

8681:4xxxx      Asia
8681:485xx      HK
8681:48501      Hong Kong Originated Supernets

8681:999xx      International
8681:99900      Unspecified Originated Supernets

Filtering Communities

JT will filter all 8681:* communities received via any external BGP peering, apart from 8681:xxxx and 8681:xx from customers, which can be used to control announcements. Any route containing improper communities will have all communities stripped and will be tagged with the special alert community of 8681:6666.

All other communities are accepted and passed unchanged and ignored.