Home > Support > Knowledge Base
Knowledge Base
 
Reset Search
Search
 

 

Knowledge

Digi TransPort BGP configuration file syntax

« Go Back

Information

 
Problem Resolution

Digi TransPort BGP configuration file syntax

DESCRIPTION
BGP on TransPort routers implements the Border Gateway Protocol version 4 as
described in RFC 4271. The following text is from the OpenBSD man page for
bgpd.conf.  The SarOS operating system implementation of BGP is almost
identical to the OpenBSD version but some of the features described may not
be supported.

SECTIONS
The BGP config file is divided into five main sections.

Macros
 User-defined variables may be defined and used later, simplifying
 the configuration file.

Global Configuration
 Global settings for BGP.

Routing Domain Configuration
 The definition and properties for BGP MPLS VPNs are set in this
 section.

Neighbors and Groups
 BGP establishes sessions with neighbors.  The neighbor
 definition and properties are set in this section, as well as
 grouping neighbors for the ease of configuration.

Filter
 Filter rules for incoming and outgoing UPDATES.

With the exception of macros, the sections should be grouped and appear
in the BGP config file in the order shown above.

The current line can be extended over multiple lines using a backslash
(`\').  Comments can be put anywhere in the file using a hash mark (`#'),
and extend to the end of the current line.  Care should be taken when
commenting out multi-line text: the comment is effective until the end of
the entire block.

Argument names not beginning with a letter, digit, or underscore must be
quoted.

MACROS
Macros can be defined that will later be expanded in context.  Macro
names must start with a letter, digit, or underscore, and may contain any
of those characters.  Macro names may not be reserved words (for example,
AS, neighbor, or group).  Macros are not expanded inside quotes.

For example:

 peer1="1.2.3.4"
 neighbor $peer1 {
 remote-as 65001
 }

GLOBAL CONFIGURATION
There are quite a few settings that affect the global operation of BGP.

AS as-number [as-number]
Set the local autonomous system number to [as-number].  If the
first AS number is a 4-byte AS it is possible to specify a
secondary 2-byte AS number which is used for neighbors which do
not support 4-byte AS numbers.  The default for the secondary AS
is 23456.

The AS numbers are assigned by local RIRs, such as:

AfriNICfor Africa
APNICfor Asia Pacific
ARIN for North America and parts of the Caribbean
LACNIC for Latin America and the Caribbean
RIPE NCC  for Europe, the Middle East, and parts of Asia

For example:

 AS 65001

sets the local AS to 65001.

The AS numbers 64512 - 65534 are designated for private use.  The
AS number 23456 is a specially designated Autonomous System
Number and should not be used.  4-byte AS numbers are specified
as two numbers separated by a dot (ASDOT format), for example:

 AS 3.10

or as a large number (ASPLAIN format), for example:

 AS 196618

connect-retry seconds
Set the number of seconds before retrying to open a connection.
This timer should be sufficiently large in EBGP configurations.
The default is 120 seconds.

fib-update (yes|no)
If set to no, do not update the Forwarding Information Base,
a.k.a. the kernel routing table.  The default is yes.

holdtime seconds
Set the holdtime in seconds.  The holdtime is reset to its
initial value every time either a KEEPALIVE or an UPDATE message
is received from the neighbor.  If the holdtime expires the
session is dropped.  The default is 90 seconds.  Neighboring
systems negotiate the holdtime used when the connection is
established in the OPEN messages.  Each neighbor announces its
configured holdtime; the smaller one is then agreed upon.

holdtime min seconds
The minimal accepted holdtime in seconds.  This value must be
greater than or equal to 3.

listen on address
Specify the local IP address BGP should listen on.

 listen on 127.0.0.1

log updates
Log received and sent updates.

network address/prefix [set ...]
network (inet|inet6) static [set ...]
network (inet|inet6) connected [set ...]
Announce the specified network as belonging to our AS.  If set to
connected, routes to directly attached networks will be
announced.  If set to static, all static routes will be
announced.

 network 192.168.7.0/24

It is possible to set default AS path attributes per network
statement:

 network 192.168.7.0/24 set localpref 220

See also the ATTRIBUTE SET section.

nexthop qualify via (bgp|default)
If set to bgp, BGP may use BGP routes to verify nexthops.  If
set to default, BGP may use the default route to verify
nexthops.  By default BGP will only use static routes or routes
added by other routing protocols like OSPF.

rde med compare (always|strict)
If set to always, the MULTI_EXIT_DISC attributes will always be
compared.  The default is strict, where the metric is only
compared between peers belonging to the same AS.

rde rib name [no evaluate]
rde rib name [rtable number]
Create an additional RIB named name.  It is possible to disable
the decision process per RIB with the no evaluate flag.  If a
rtable is specified, routes will be exported to the given kernel
routing table.  Currently the routing table must belong to the
default routing domain and nexthop verification happens on table
0.  Routes in the specified table will not be considered for
nexthop verification.  Adj-RIB-In and Loc-RIB are created
automatically and used as default.

rde route-age (ignore|evaluate)
If set to evaluate, the best path selection will not only be
based on the path attributes but also on the age of the route,
giving preference to the older, typically more stable, route.  In
this case the decision process is no longer deterministic.  The
default is ignore.

route-collector (yes|no)
If set to yes, the route selection process is turned off.  The
default is no.

router-id address
Set the router ID to the given IP address, which must be local to
the machine.

 router-id 10.0.0.1

If not given, the BGP ID is determined as the biggest IP address
assigned to the local machine.

rtable number
Work with the given kernel routing table instead of the default
table, 0.  Note that table 0 is used for nexthop verification.
Routes in the specified table will not be considered for nexthop
verification.  This is the same as using the following syntax:

 rde rib Loc-RIB rtable number

transparent-as (yes|no)
If set to yes, AS paths to EBGP neighbors are not prepended with
their own AS.  The default is no.

ROUTING DOMAIN CONFIGURATION
BGP supports the setup and distribution of Virtual Private Networks.
It is possible to import and export prefixes between routing domains.
Each routing domain is specified by an rdomain section, which allows
properties to be set specifically for that rdomain:

 rdomain 1 {
 descr "a rdomain"
 rd 65002:1
 import-target rt 65002:42
 export-target rt 65002:42
 network 192.168.1/24
 depend on mpe0
 }

There are several routing domain properties:

depend on interface
Routes added to the rdomain will use this interface as the
outgoing interface.  Normally this will be an MPLS Provider Edge,
mpe(4), interface that is part of the rdomain.  Local networks
will be announced with the MPLS label specified on the interface.

descr description
Add a description.  The description is used when logging but has
no further meaning to BGP.

export-target subtype as-number:local
export-target subtype IP:local
Specify an extended community which will be attached to announced
networks.  More than one export-target can be specified.  See
also the ATTRIBUTE SET section for further information about the
encoding.  The subtype should be set to rt for best compatibility
with other implementations.

fib-update (yes|no)
If set to no, do not update the Forwarding Information Base,
a.k.a. the kernel routing table.  The default is yes.

import-target subtype as-number:local
import-target subtype IP:local
Only prefixes matching one of the specified import-targets will
be imported into the rdomain.  More than one import-target can be
specified.  See also the ATTRIBUTE SET section for further
information about the encoding of extended communities.  The
subtype should be set to rt for best compatibility with other
implementations.

network arguments ...
Define which networks should be exported into this VPN.  See also
the nexthop section in GLOBAL CONFIGURATION for further
information about the arguments.

rd as-number:local
rd IP:local
The sole purpose of the Route Distinguisher rd is to ensure that
possible common prefixes are destinct between VPNs.  The rd is
neither used to identify the origin of the prefix nor to control
into which VPNs the prefix is distributed to.  The as-number or
IP of a rd should be set to a number or IP that was assigned by
an appropriate authority.  Whereas local can be chosen by the
local operator.

NEIGHBORS AND GROUPS
BGP establishes TCP connections to other BGP speakers called
neighbors.  Each neighbor is specified by a neighbor section, which
allows properties to be set specifically for that neighbor:

 neighbor 10.0.0.2 {
 remote-as 65002
 descr "a neighbor"
 }

Multiple neighbors can be grouped together by a group section.  Each
neighbor section within the group section inherits all properties from
its group:

 group "peering AS65002" {
 remote-as 65002
 neighbor 10.0.0.2 {
  descr "AS65002-p1"
 }
 neighbor 10.0.0.3 {
  descr "AS65002-p2"
 }
 }

Instead of the neighbor's IP address, an address/netmask pair may be
given:

 neighbor 10.0.0.0/8

In this case, the neighbor specification becomes a template, and if a
neighbor connects from an IP address within the given network, the
template is cloned, inheriting everything from the template but the
remote address, which is replaced by the connecting neighbor's address.
With a template specification it is valid to omit remote-as; BGP will
then accept any AS the neighbor presents in the OPEN message.

There are several neighbor properties:

announce (all|none|self|default-route)
If set to none, no UPDATE messages will be sent to the neighbor.
If set to default-route, only the default route will be announced
to the neighbor.  If set to all, all generated UPDATE messages
will be sent to the neighbor.  This is usually used for transit
AS's and IBGP peers.  The default value for EBGP peers is self,
which limits the sent UPDATE messages to announcements of the
local AS.  The default for IBGP peers is all.

announce (IPv4|IPv6) (none|unicast|vpn)
For the given address family, control which subsequent address
families (at the moment, only none, which disables the
announcement of that address family, unicast, and vpn, which
allows the distribution of BGP MPLS VPNs, are supported) are
announced during the capabilities negotiation.  Only routes for
that address family and subsequent address family will be
announced and processed.

announce as-4byte (yes|no)
If set to no, the 4-byte AS capability is not announced and so
native 4-byte AS support is disabled.  The default is yes.

announce capabilities (yes|no)
If set to no, capability negotiation is disabled during the
establishment of the session.  This can be helpful to connect to
old or broken BGP implementations.  The default is yes.

announce refresh (yes|no)
If set to no, the route refresh capability is not announced.  The
default is yes.

announce restart (yes|no)
If set to yes, the graceful restart capability is announced.
Currently only the End-of-RIB marker is supported and announced
by the restart capability.  The default is no.

demote group
Increase the demotion counter on the given interface
group, when the session is not in state ESTABLISHED.
The demotion counter will be increased as soon as
BGP starts and decreased 60 seconds after the session went to
state ESTABLISHED.  For neighbors added at runtime, the demotion
counter is only increased after the session has been ESTABLISHED
at least once before dropping.

depend on interface
The neighbor session will be kept in state IDLE as long as
interface reports no link.
The state of the network interfaces on the system can be viewed
using the 'route print' command.

descr description
Add a description.  The description is used when logging neighbor
events, in status reports, for specifying neighbors, etc., but
has no further meaning to BGP.

down Do not start the session when bgpd comes up but stay in IDLE.

dump (all|updates) (in|out) file [timeout]
Do a peer specific MRT dump.  Peer specific dumps are limited to
all and updates.  See also the dump section in GLOBAL
CONFIGURATION.

enforce neighbor-as (yes|no)
If set to yes, AS paths whose leftmost AS is not equal to the
remote AS of the neighbor are rejected and a NOTIFICATION is sent
back.  The default value for IBGP peers is no otherwise the
default is yes.

holdtime seconds
Set the holdtime in seconds.  Inherited from the global
configuration if not given.

holdtime min seconds
Set the minimal acceptable holdtime.  Inherited from the global
configuration if not given.

local-address address
When BGP initiates the TCP connection to the neighbor system,
it normally does not bind to a specific IP address.  If a
local-address is given, BGP binds to this address first.

max-prefix number [restart number]
Terminate the session after number prefixes have been received
(no such limit is imposed by default).  If restart is specified,
the session will be restarted after number minutes.

multihop hops
Neighbors not in the same AS as the local BGP normally have
to be directly connected to the local machine.  If this is not
the case, the multihop statement defines the maximum hops the
neighbor may be away.

passive
Do not attempt to actively open a TCP connection to the neighbor
system.

remote-as as-number
Set the AS number of the remote system.

rib name
Bind the neighbor to the specified RIB.

route-reflector [address]
Act as an RFC 4456 route-reflector for this neighbor.  An
optional cluster ID can be specified; otherwise the BGP ID will
be used.

set attribute ...
Set the AS path attributes to some default per neighbor or group
block:

 set localpref 300

See also the ATTRIBUTE SET section.  Set parameters are applied
to the received prefixes; the only exceptions are prepend-self,
nexthop no-modify and nexthop self.  These sets are rewritten
into filter rules.

softreconfig (in|out) (yes|no)
Turn soft reconfiguration on or off for the specified direction.
If soft reconfiguration is turned on, filter changes will be
applied on configuration reloads.  If turned off, a BGP session
needs to be cleared to apply the filter changes.  Enabling
softreconfig in will raise the memory requirements of BGP
because the unmodified AS path attributes need to be stored as
well.  The default is yes.

tcp md5sig password secret
tcp md5sig key secret
Enable TCP MD5 signatures per RFC 2385.  The shared secret can
either be given as a password or hexadecimal key.

 tcp md5sig password mekmidasdigoat
 tcp md5sig key deadbeef

transparent-as (yes|no)
If set to yes, AS paths to EBGP neighbors are not prepended with
their own AS.  The default is inherited from the global
transparent-as setting.

ttl-security (yes|no)
Enable or disable ttl-security.  When enabled, outgoing packets
are sent using a TTL of 255 and a check is made against an
incoming packet's TTL.  For directly connected peers, incoming
packets are required to have a TTL of 255, ensuring they have not
been routed.  For multihop peers, incoming packets are required
to have a TTL of 256 minus multihop distance, ensuring they have
not passed through more than the expected number of hops.  The
default is no.

FILTER
BGP has the ability to allow and deny UPDATES based on prefix or AS
path attributes.  In addition, UPDATES may also be modified by filter
rules.

For each UPDATE processed by the filter, the filter rules are evaluated
in sequential order, from first to last.  The last matching allow or deny
rule decides what action is taken.

The following actions can be used in the filter:

allowThe UPDATE is passed.

deny The UPDATE is blocked.

matchApply the filter attribute set without influencing the filter
decision.

PARAMETERS
The rule parameters specify the UPDATES to which a rule applies.  An
UPDATE always comes from, or goes to, one neighbor.  Most parameters are
optional, but each can appear at most once per rule.  If a parameter is
specified, the rule only applies to packets with matching attributes.

as-type as-number
This rule applies only to UPDATES where the AS path matches.  The
as-number is matched against a part of the AS path specified by
the as-type.  as-number may be set to neighbor-as, which is
expanded to the current neighbor remote AS number.  as-type is
one of the following operators:

AS (any part)
peer-as (leftmost AS number)
source-as (rightmost AS number)
transit-as(all but the rightmost AS number)

Multiple as-number entries for a given type or as-type as-number
entries may also be specified, separated by commas or whitespace,
if enclosed in curly brackets:

 deny from any AS { 1, 2, 3 }
 deny from any { AS 1, source-as 2, transit-as 3 }
 deny from any { AS { 1, 2, 3 }, source-as 4, transit-as 5 }

community as-number:local
community name
This rule applies only to UPDATES where the community path
attribute is present and matches.  Communities are specified as
as-number:local, where as-number is an AS number and local is a
locally significant number between zero and 65535.  Both
as-number and local may be set to `*' to do wildcard matching.
Alternatively, well-known communities may be given by name
instead and include NO_EXPORT, NO_ADVERTISE, NO_EXPORT_SUBCONFED,
and NO_PEER.  Both as-number and local may be set to neighbor-as,
which is expanded to the current neighbor remote AS number.

ext-community subtype as-number:local
ext-community subtype IP:local
ext-community subtype numvalue
This rule applies only to UPDATES where the extended community
path attribute is present and matches.  Extended Communities are
specified by a subtype and normally two values, a globally unique
part (e.g. the AS number) and a local part.  See also the
ATTRIBUTE SET section for further information about the encoding.

(from|to) peer
This rule applies only to UPDATES coming from, or going to, this
particular neighbor.  This parameter must be specified.  peer is
one of the following:

anyAny neighbor will be matched.
address Neighbors with this address will be matched.
group descr  Neighbors in this group will be matched.

Multiple peer entries may also be specified, separated by commas
or whitespace, if enclosed in curly brackets:

 deny from { 128.251.16.1, 251.128.16.2, group hojo }

(inet|inet6)
This rule applies only to routes matching the stated address
family.  The address family needs to be set only in rules that
use prefixlen without specifying a prefix beforehand.

max-as-len len
This rule applies only to UPDATES where the AS path has more than
len elements.

max-as-seq len
This rule applies only to UPDATES where a single AS number is
repeated more than len times.

prefix address/len
This rule applies only to UPDATES for the specified prefix.

Multiple address/len entries may be specified, separated by
commas or whitespace, if enclosed in curly brackets:

 deny from any prefix { 192.168.0.0/16, 10.0.0.0/8 }

Multiple lists can also be specified, which is useful for macro
expansion:

 good="{ 192.168.0.0/16, 172.16.0.0/12, 10.0.0.0/8 }"
 bad="{ 224.0.0.0/4, 240.0.0.0/4 }"
 ugly="{ 127.0.0.1/8, 169.254.0.0/16 }"

 deny from any prefix { $good $bad $ugly }

prefixlen range
This rule applies only to UPDATES for prefixes where the
prefixlen matches.  Prefix length ranges are specified by using
these operators:

 =  (equal)
 != (unequal)
 <  (less than)
 <= (less than or equal)
 >  (greater than)
 >= (greater than or equal)
 -  (range including boundaries)
 >< (except range)

>< and - are binary operators (they take two arguments).  For
instance, to match all prefix lengths >= 8 and <= 12, and hence
the CIDR netmasks 8, 9, 10, 11 and 12:

 prefixlen 8-12

Or, to match all prefix lengths < 8 or > 12, and hence the CIDR
netmasks 0-7 and 13-32:

 prefixlen 8><12

prefixlen can be used together with prefix.

This will match all prefixes in the 10.0.0.0/8 netblock with
netmasks longer than 16:

 prefix 10.0.0.0/8 prefixlen > 16

quickIf an UPDATE matches a rule which has the quick option set, this
rule is considered the last matching rule, and evaluation of
subsequent rules is skipped.

rib name
Apply rule only to the specified RIB.  This only applies for
received updates, so not for rules using the to peer parameter.

set attribute ...
All matching rules can set the AS path attributes to some
default.  The set of every matching rule is applied, not only the
last matching one.  See also the following section.

ATTRIBUTE SET
AS path attributes can be modified with set.

set can be used on network statements, in neighbor or group blocks, and
on filter rules.  Attribute sets can be expressed as lists.

The following attributes can be modified:

community [delete] as-number:local
community [delete] name
Set or delete the COMMUNITIES AS path attribute.  Communities are
specified as as-number:local, where as-number is an AS number and
local is a locally-significant number between zero and 65535.
Alternately, well-known communities may be specified by name:
NO_EXPORT, NO_ADVERTISE, NO_EXPORT_SUBCONFED, or NO_PEER.

ext-community [delete] subtype as-number:local
ext-community [delete] subtype IP:local
ext-community [delete] subtype numvalue
Set or delete the Extended Community AS path attribute.  Extended
Communities are specified by a subtype and normally two values, a
globally unique part (e.g. the AS number) and a local part.  The
type is selected depending on the encoding of the global part.
Two-octet AS Specific Extended Communities and Four-octet AS
Specific Extended Communities are encoded as as-number:local.
Four-octet encoding is used if the as-number is bigger then 65535
or if the AS_DOT encoding is used.  IPv4 Address Specific
Extended Communities are encoded as IP:local.  Opaque Extended
Communities are encoded with a single numeric value.  Currently
the following subtypes are supported:

 rt  Route Target
 soo Source of Origin
 odi OSPF Domain Identifier
 ort OSPF Route Type
 ori OSPF Router ID
 bdc BGP Data Collection

Not all type and subtype value pairs are allowed by IANA and the
parser will ensure that no invalid combination is created.

localpref number
Set the LOCAL_PREF AS path attribute.  If number starts with a
plus or minus sign, LOCAL_PREF will be adjusted by adding or
subtracting number; otherwise it will be set to number.  The
default is 100.

med number
metric number
Set the MULTI_EXIT_DISC AS path attribute.  If number starts with
a plus or minus sign, MULTI_EXIT_DISC will be adjusted by adding
or subtracting number; otherwise it will be set to number.

origin (igp|egp|incomplete)
Set the ORIGIN AS path attribute to mark the source of this route
as being injected from an igp protocol, an egp protocol or being
an aggregated route.

nexthop (address|blackhole|reject|self|no-modify)
Set the NEXTHOP AS path attribute to a different nexthop address
or use blackhole or reject routes.  If set to no-modify, the
nexthop attribute is not modified.  Unless set to self, the
nexthop is left unmodified for IBGP sessions.  self forces the
nexthop to be set to the local interface address.

 set nexthop 192.168.0.1
 set nexthop blackhole
 set nexthop reject
 set nexthop no-modify
 set nexthop self

prepend-neighbor number
Prepend the neighbor's AS number times to the AS path.

prepend-self number
Prepend the local AS number times to the AS path.

rtlabel label
Add the prefix to the kernel routing table with the specified
label.

weight number
The weight is used to tip prefixes with equally long AS paths in
one or the other direction.  A prefix is weighed at a very late
stage in the decision process.  If number starts with a plus or
minus sign, the weight will be adjusted by adding or subtracting
number; otherwise it will be set to number.  Weight is a local
non-transitive attribute and a bgpd-specific extension.  For
prefixes with equally long paths, the prefix with the larger
weight is selected.



BG  3/10/14

Feedback

 

Was this article helpful?


   

Feedback

Please tell us how we can make this article more useful.

Characters Remaining: 255