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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.
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
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.
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.
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
| Command or Action | Purpose | |
|---|---|---|
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Step 1 |
enable Example: |
Enables privileged EXEC mode.
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Step 2 |
configure terminal Example: |
Enters global configuration mode. |
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Step 3 |
router bgp as-number Example: |
Configures a Boarder Gateway Protocol (BGP) routing process and enters router configuration mode. |
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Step 4 |
address-family {vpnv4 | vpnv6 } unicast Example: |
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: |
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. |
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Step 6 |
address-family rtfilter Example: |
Specifies the RT filter address family type. |
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Step 7 |
end Example: |
Exits address family configuration mode and returns to privileged EXEC mode. |
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Step 8 |
show ip bgp vpnv4 all update-group update-group Example: |
(Optional) Displays the information about neighbors in the update group. |
|
Step 9 |
show ip bgp vpnv4 all neighbors {ip-address | ipv6-address} Example: |
(Optional) Displays information about the BGP VPNv4 neighbor. |
|
Step 10 |
show ip bgp vpnv4 all peer-group Example: |
(Optional) Displays information about the peer groups. |
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Step 11 |
debug ip bgp all updates in Example: |
(Optional) Displays BGP update messages. |
Configuration Examples for BGP-RTC for Legacy PE
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-familyThe 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 outThe 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| Related Topic | Document Title |
|---|---|
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Cisco IOS commands |
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BGP commands |
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Configuring BGP: RT Constrained Route Distribution |
"Configuring BGP: RT Constrained Route Distribution" module in the IP Routing: BGP Configuration Guide |
| Standard/RFC | Title |
|---|---|
|
RFC 4684 |
Constrained Route Distribution for Border Gateway Protocol/MultiProtocol Label Switching (BGP/MPLS) Internet Protocol (IP) Virtual Private Networks (VPNs) |
| Description | Link |
|---|---|
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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.
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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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