BGP-RTC for Legacy PE
The BGP-Route Target
Constrain (RTC) for Legacy PE feature helps to prevent the propagation of VPN
Network Layer Reachability Information (NLRI) to a provider edge (PE) device
that is not interested in the VPN. This feature builds an outbound filter used
by a Boarder Gateway Protocol (BGP) speaker to decide which routes to pass to
its peer and propagates route target (RT) reachability information between
internal BGP (iBGP) meshes.
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Prerequisites for BGP-RTC
for Legacy PE
Before you
configure the BGP-RTC for Legacy PE feature, you must configure the RT filter
unicast address family type. For more information, see "Configuring BGP: RT
Constrained Route Distribution" module in the
IP Routing: BGP
Configuration Guide.
Information About BGP-RTC for Legacy PE
Overview of
BGP-RTC for Legacy PE
The BGP—RTC for
Legacy PE feature makes use of VPN unicast route exchange from the legacy
provider edge (PE) devices to a new Boarder Gateway Protocol (BGP) speaker
(route reflector [RR]) to signal route target (RT) membership. The legacy PEs
announce a set of special routes with mapped RTs to the RR along with a
standard community. The presence of the community triggers the RR to extract
the RTs and build RT membership information.
In scenarios where
VPN membership is normal, this functionality helps reduce the scaling
requirements on the PE devices and the RRs. The PE devices need not to spend
resources for filtering out unwanted routes. The BGP peers that have common
outbound policies are grouped under a single format group. Separate replication
groups are used within a format group to separate BGP peers with its own
peer-based policies. The Route Target Constrain (RTC)-capable peers are placed
in separate format groups. Each RTC peers have a separate replication group.
When legacy RT is configured for a peer, then it must be treated the same way
as the RTC peer except that there is no capability negotiation.
Legacy PE
Support-PE Behavior
Each legacy Route
Target Constrain (RTC) speaking neighbor is assigned a separate replication
group. BGP checks the VPN table for any route with a reserved community value
and uses it to create RTC network from the VPN prefix received from a legacy
RTC peer with community values. The PE device uses the existing VPN
advertisement mechanism to convey route target (RT) membership from the legacy
provider edge (PE) devices. The route reflector (RR) processes advertisement
mechanisms of RT membership information from legacy PE devices. RRs translate
the legacy PE RT membership information to equivalent RTC Network Layer
Reachability Information (NLRIs) to propagate to other RRs.
Legacy PE
Support-RR Behavior
Route reflectors
(RR) identify routes from legacy provider edge (PE) devices for retrieving
route target (RT) membership information by the community value and filter VPN
routes to legacy PE devices. RRs use the existing VPN advertisement mechanism
to convey and process RT membership from the legacy PEs. The legacy PE RT
membership information is translated into equivalent RT membership Network
Layer Reachability Information (NLRI) from the client to propagate to other
RRs. The RR then creates the route target filter list for each legacy client by
collecting the entire set of route targets.
How to Configure BGP-RTC for Legacy PE
Configuring BGP-RTC for
Legacy PE
SUMMARY STEPS1.
enable
2.
configure
terminal
3.
router
bgp
as-number
4.
address-family
{vpnv4 |
vpnv6 }
unicast
5.
neighbor
{ip-address |
peer-group-name |
ipv6-address}
accept-route-legacy-rt
6.
address-family rtfilter
7.
end
8.
show ip
bgp vpnv4 all update-group
update-group
9.
show ip
bgp vpnv4 all neighbors
{ip-address
|
ipv6-address}
10.
show ip
bgp vpnv4 all peer-group
11.
debug ip
bgp all updates in
DETAILED STEPS| | Command or Action | Purpose |
|---|
| Step 1 |
enable
Example:
|
Enables
privileged EXEC mode.
|
| Step 2 |
configure
terminal
Example:
Device# configure terminal
|
Enters global
configuration mode.
|
| Step 3 |
router
bgp
as-number
Example:
Device(config)# router bgp 1
|
Configures a
Boarder Gateway Protocol (BGP) routing process and enters router configuration
mode.
|
| Step 4 |
address-family
{vpnv4 |
vpnv6 }
unicast
Example:
Device(config-router)# address-family vpnv4 unicast
|
Specifies the
VPNv4 or VPNv6 address family and enters address family configuration mode.
|
| Step 5 |
neighbor
{ip-address |
peer-group-name |
ipv6-address}
accept-route-legacy-rt
Example:
Device(config-router-af)# neighbor 10.0.0.1 accept-route-legacy-rt
|
Configures
the neighbor on the route reflector (RR) to treat the provider edge (PE) device
as a legacy PE for the route target (RT) and accepts VPN routes tagged with the
special community.
|
| Step 6 |
address-family rtfilter
Example:
Device(config-router-af)# address-family rtfilter
|
Specifies
the RT filter address family type.
|
| Step 7 |
end
Example:
Device(config-router-af)# end
|
Exits address
family configuration mode and returns to privileged EXEC mode.
|
| Step 8 |
show ip
bgp vpnv4 all update-group
update-group
Example:
Device# show ip bgp vpnv4 all update-group 2
|
(Optional)
Displays the information about neighbors in the update group.
|
| Step 9 |
show ip
bgp vpnv4 all neighbors
{ip-address
|
ipv6-address}
Example:
Device# show ip bgp vpnv4 all neighbors 192.168.3.3
|
(Optional)
Displays information about the BGP VPNv4 neighbor.
|
| Step 10 |
show ip
bgp vpnv4 all peer-group
Example:
Device# show ip bgp vpnv4 all peer-group
|
(Optional)
Displays information about the peer groups.
|
| Step 11 |
debug ip
bgp all updates in
Example:
Device# debug ip bgp all updates in
|
(Optional)
Displays BGP update messages.
|
Configuration Examples for BGP-RTC for Legacy PE
Example: BGP-RTC for Legacy
PE
Configuration
on the Route Reflector
The following
example shows how to configure the neighbor on the route reflector (RR) to
treat the provider edge (PE) device as a legacy PE for the route target (RT)
and accept VPN routes tagged with the special community:
Device# configure terminal
Device(config)# router bgp 1
Device(config-router)# address-family vpnv4 unicast
Device(config-router-af)# neighbor 10.1.1.1 accept-route-legacy-rt
Device(config-router-af)# address-family rtfilter
Device(config-router-af)# exit address-family
Configuration
on the Legacy PE
The following
example shows how to create a route filter VRF and attach an export map that
collects and carries all RTs locally configured on Layer 3 VPN virtual routing
and forwarding (VRF):
ip vrf route-filter
rd 55:1111
export map SET_RT
route-map SET_RT permit 10
match ip address prefix-list RT_NET1
set community 4294901762 (0xFFFF0002)
set extcommunity rt 255.220.0.0:12241 255.220.0.0:12242 additive
set extcommunity rt 255.220.0.0:12243 255.220.0.0:12244 additive
set extcommunity rt 255.220.0.0:12245 255.220.0.0:12246 additive
set extcommunity rt 255.220.0.0:12247 255.220.0.0:12248 additive
set extcommunity rt 255.220.0.0:12249 255.220.0.0:12250 additive
!
route-map SET_RT permit 20
match ip address prefix-list RT_NET2
set community 4294901762 (0xFFFF0002)
set extcommunity rt 255.220.0.0:12251 255.220.0.0:12252 additive
set extcommunity rt 255.220.0.0:12253 255.220.0.0:12254 additive
set extcommunity rt 255.220.0.0:12255 additive
!
ip route vrf route-filter 5.5.5.5 255.255.255.255 Null0 – (matching prefix-set RT_NET1)
ip route vrf route-filter 6.6.6.6 255.255.255.255 Null0 –(matching prefix-set RT_NET2)
route-map LEG_PE permit 10
match ip address prefix-list RT_NET1 RT_NET2
set community no-advertise additive
The following
example shows how to apply the route map to a VPNv4 neighbor:
router bgp 55
address-family vpnv4 unicast
neighbor x.x.x.x route-map LEG_PE out
The following
example shows how to source a static route into a Boarder Gateway Protocol
(BGP) network using a network statement:
router bgp 55
address-family ipv4 vrf route-filter
network 5.5.5.5 mask 255.255.255.255
network 6.6.6.6 mask 255.255.255.255
Additional
References for BGP-RTC for Legacy PE
Standards and
RFCs
| Standard/RFC
|
Title
|
|---|
|
RFC 4684
|
Constrained Route
Distribution for Border Gateway Protocol/MultiProtocol Label Switching
(BGP/MPLS) Internet Protocol (IP) Virtual Private Networks (VPNs)
|
Technical
Assistance
| Description
|
Link
|
|---|
|
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|
http://www.cisco.com/support
|
Feature
Information for BGP-RTC for Legacy PE
The following table provides release information about the feature or features described in this module. This table lists only the software release that introduced support for a given feature in a given software release train. Unless noted otherwise, subsequent releases of that software release train also support that feature.
Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to www.cisco.com/go/cfn. An account on Cisco.com is not required.
Table 1 Feature
Information for BGP-RTC for Legacy PE|
Feature
Name
|
Releases
|
Feature
Information
|
|---|
|
BGP-RTC
for Legacy PE
|
|
The
BGP-RTC for Legacy PE feature helps to prevent the propagation of VPN Network
Layer Reachability Information (NLRI) to a provider edge (PE) device that is
not interested in the VPN. This feature builds an outbound filter used by a
Boarder Gateway Protocol (BGP) speaker to decide which routes to pass to its
peer and propagates route target (RT) reachability information between internal
BGP (iBGP) meshes.
The
neighbor
accept-route-legacy-rt
command was introduced.
|
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