BGP-VRF-Aware Conditional Advertisement

The Border Gateway Protocol (BGP) VRF-Aware Conditional Advertisement feature provides additional control of the advertisement of routes and extends this control to within a virtual routing and forwarding (VRF) instance.

Information About BGP VRF-Aware Conditional Advertisement

VRF-Aware Conditional Advertisement

The Border Gateway Protocol (BGP) VRF-Aware Conditional Advertisement feature provides additional control of the advertisement of routes and extends this control within a virtual routing and forwarding (VRF) instance.

BGP Conditional Advertisement

Normally, routes are propagated regardless of the existence of a different route. The BGP conditional advertisement feature uses the exist-map , non-exist-map , and the advertise-map keywords of the neighbor command in order to track routes by the route prefix. If a route prefix is not present in output of the non-exist-map command, then the route specified by the advertise-map is announced. This feature is useful for multihomed networks, in which some prefixes are advertised to one of the providers only if information from the other provider is not present (this indicates a failure in the peering session or partial reachability). The conditional BGP announcements are sent in addition to the normal announcements that a BGP router sends to its peers.

VRF-Aware Conditional Advertisement

This feature extends support for BGP VRF-aware conditional advertisement to the following address families:

  • IPv4 unicast

  • IPv4 unicast VRF

  • IPv6 unicast

  • IPv6 unicast VRF

Figure 1. VRF-Based Conditional Advertisement
The figure above shows the IPv4 prefix 192.168.50.0/24 being advertised by a remote CE101 into VRF RED on PE1. The prefix flows as a MP-BGP VPN prefix and is imported into the VRF RED on PE4. On the PE4 the conditions configured by the exist-map command relating to this prefix in the BGP VRF RED table becomes the condition to advertise the prefix 203.0.113.0/24 to the CE104, that is, peer-activated under the VRF RED on the PE4. This scenario assumes that 203.0.113.0/24 is in the VRF RED BGP table. If 203.0.113.0/24 is not in the table, this policy is ignored.

  • If 192.168.50.0/24 exists in PE4’s BGP table, then the 203.0.113.0/24 network is advertised to CE104.

  • If 192.168.50.0/24 does not exist in PE4’s BGP table, then the 203.0.113.0/24 network is not advertised to CE104.

How to Configure BGP VRF-Aware Conditional Advertisement

Configuring BGP VRF-Aware Conditional Advertisement

SUMMARY STEPS

  1. enable
  2. configure terminal
  3. router bgp autonomous-system-number
  4. Enter one of the following:
    • address-family ipv4 [unicast] [vrf vrf-name]
    • address-family ipv6 [unicast] [vrf vrf-name]
  5. neighbor {ip-address | ipv6-address} remote-as autonomous-system-number
  6. neighbor {ip-address | ipv6-address} activate
  7. neighbor {ip-address | ipv6-address} advertise-map map-name {exist-map map-name | non-exist-map map-name}
  8. end

DETAILED STEPS

  Command or Action Purpose

Step 1

enable

Example:


Device> enable

Enables privileged EXEC mode.

  • Enter your password if prompted.

Step 2

configure terminal

Example:


Device# configure terminal

Enters global configuration mode.

Step 3

router bgp autonomous-system-number

Example:


Device(config)# router bgp 40000

Enters router configuration mode for the specified routing process.

Step 4

Enter one of the following:

  • address-family ipv4 [unicast] [vrf vrf-name]
  • address-family ipv6 [unicast] [vrf vrf-name]

Example:


Device(config-router)# address-family ipv4 vrf VRFRED

Specifies the IPv4 or IPv6 address family and enters address family configuration mode.

  • The unicast keyword specifies the IPv4 or IPv6 unicast address family.

  • The vrf keyword and vrf-name argument specify the name of the virtual routing and forwarding (VRF) instance to associate with subsequent IPv4 or IPv6 address family configuration mode commands.

Step 5

neighbor {ip-address | ipv6-address} remote-as autonomous-system-number

Example:


Device(config-router-af)# neighbor 192.0.2.1 remote-as 104

Adds the IP address of the neighbor in the specified autonomous system to the IPv4 or IPv6 multiprotocol BGP neighbor table of the local device.

Step 6

neighbor {ip-address | ipv6-address} activate

Example:


Device(config-router-af)# neighbor 192.0.2.1 activate

Enables the neighbor to exchange prefixes for the IPv4 or IPv6 address family with the local device.

Step 7

neighbor {ip-address | ipv6-address} advertise-map map-name {exist-map map-name | non-exist-map map-name}

Example:


Device(config-router-af)# neighbor 192.0.2.1 advertise-map ADV-1 exist-map EXIST-1

Enables conditional advertisement towards a neighbor to allow the advertisement of prefixes mapped by the advertise-map command based on the criteria defined under exist or non-exist maps.

  • The advertise-map map-name keyword-argument pair specifies the name of the route map used to define the advertised routes.

  • The exist-map map-name keyword-argument pair specifies the condition that can be satisfied by a set of routes in the BGP table. If the condition is satisfied then the routes in the BGP table matching those specified in advertise map will be advertised. If the routes matching those specified in exist-map do not exist in the BGP table, those routes will not be advertised.

  • The non-exist-map map-name keyword-argument pair specifies the condition that is compared to a set of routes in the BGP table. If the routes in the non-exist-map are not present in the BGP table, then the routes matching those specified in advertise map will be advertised. If the routes matching those specified in non-exist-map are present in the BGP table, then the routes matching advertise-map will not be advertised.

Step 8

end

Example:


Device(config-router-af)# end

Exits address family configuration mode and enters privileged EXEC mode.

What to do next

To verify the configuration of the BGP VRF-Aware Conditional Advertisement feature, use the show bgp ip neighbors command.

Configuration Examples for BGP VRF-Aware Conditional Advertisement

Example: Configuring BGP VRF-Aware Conditional Advertisement

The following examples use the configuration in figure 1:

CE 101: The source of the prefixes

router bgp 101
 bgp log-neighbor-changes
 timers bgp 0 0
 neighbor 172.16.1.2 remote-as 65000
 !
 address-family ipv4
  network 21.21.21.0 mask 255.255.255.0
  network 22.22.22.22 mask 255.255.255.255
  network 31.0.0.0
  network 33.0.0.0
  network 44.0.0.0
  network 192.0.254 mask 255.255.255.0
  network 192.0.2.50
  neighbor 172.16.1.3 activate
 exit-address-family

PE 1


router bgp 65000
 bgp log-neighbor-changes
 no bgp default ipv4-unicast
 timers bgp 0 0
 neighbor 10.0.0.2 remote-as 65000
 neighbor 10.0.0.2 update-source Loopback0
 !
 address-family ipv4
 exit-address-family
 !
 address-family vpnv4
  neighbor 10.0.0.2 activate
  neighbor 10.0.0.2 send-community both
 exit-address-family
 !
 address-family ipv4 vrf blue
  neighbor 198.51.100.10 remote-as 201
  neighbor 198.51.100.10 activate
 exit-address-family
 !
 address-family ipv4 vrf red
  neighbor 172.16.1.2 remote-as 101
  neighbor 172.16.1.2 activate
 exit-address-family

PE 4

router bgp 65000
 bgp log-neighbor-changes
 no bgp default ipv4-unicast
 timers bgp 0 0
 neighbor 10.0.0.2 remote-as 65000
 neighbor 10.0.0.2 update-source Loopback0
 !
 address-family ipv4
 exit-address-family
 !
 address-family vpnv4
  neighbor 10.0.0.2 activate
  neighbor 10.0.0.2 send-community extended
 exit-address-family
 !
 address-family ipv4 vrf blue
  neighbor 198.51.100.12 remote-as 204
  neighbor 198.51.100.12 activate
 exit-address-family
 !
 address-family ipv4 vrf red
  neighbor 198.51.100.3 remote-as 104
  neighbor 198.51.100.3 activate
  neighbor 198.51.100.3 advertise-map ADV-1 exist-map EXIST-1
  neighbor 198.51.100.3 advertise-map ADV-2 exist-map EXIST-2
  neighbor 198.51.100.3 advertise-map ADV-3 exist-map EXIST-3
  neighbor 198.51.100.3 advertise-map ADV-4 exist-map EXIST-4
 exit-address-family
!
ip prefix-list pl-adv-1 seq 5 permit 22.22.22.22/32
!         
ip prefix-list pl-adv-2 seq 5 permit 44.0.0.0/8 
!         
ip prefix-list pl-adv-3 seq 5 permit 33.0.0.0/8
!         
ip prefix-list pl-adv-4 seq 5 permit 128.16.16.0/24
!         
ip prefix-list pl-exist-1 seq 5 permit 21.21.21.0/24
!         
ip prefix-list pl-exist-2 seq 5 permit 41.0.0.0/8 
!         
ip prefix-list pl-exist-3 seq 5 permit 31.0.0.0/8
!         
ip prefix-list pl-exist-4 seq 5 permit 192.168.50.0/24
!         
route-map EXIST-4 permit 10
 match ip address prefix-list pl-exist-4
!         
route-map ADV-4 permit 10
 match ip address prefix-list pl-adv-4
!         
route-map EXIST-2 permit 10
 match ip address prefix-list pl-exist-2
!         
route-map ADV-2 permit 10
 match ip address prefix-list pl-adv-2
!         
route-map EXIST-3 permit 10
 match ip address prefix-list pl-exist-3
!         
route-map ADV-3 permit 10
 match ip address prefix-list pl-adv-3
!         
route-map EXIST-1 permit 10
 match ip address prefix-list pl-exist-1
!         
route-map ADV-1 permit 10
 match ip address prefix-list pl-adv-1

Example: Verifying BGP VRF-Aware Conditional Advertisement

The following examples use the configuration in figure 1:

CE 101


CE101# show ip bgp all

For address family: IPv4 Unicast
BGP table version is 28, local router ID is 203.0.113.11
     Network          Next Hop            Metric LocPrf Weight Path
 *>  21.21.21.0/24     0.0.0.0                  0         32768 i
 *>  22.22.22.22/32    0.0.0.0                  0         32768 i
 *>  31.0.0.0          0.0.0.0                  0         32768 i
 *>  33.0.0.0          0.0.0.0                  0         32768 i
 *>  44.0.0.0          0.0.0.0                  0         32768 i
 *>  192.0.2.254/24    0.0.0.0                  0         32768 i
 *>  192.0.2.50        0.0.0.0                  0         32768 i

PE 1


PE1# show ip bgp all

For address family: IPv4 Unicast


For address family: VPNv4 Unicast

BGP table version is 46, local router ID is 10.0.0.1
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal, 
              r RIB-failure, S Stale, m multipath, b backup-path, f RT-Filter, 
              x best-external, a additional-path, c RIB-compressed, 
Origin codes: i - IGP, e - EGP, ? - incomplete
RPKI validation codes: V valid, I invalid, N Not found

     Network          Next Hop            Metric LocPrf Weight Path
Route Distinguisher: 1:1 (default for vrf red)
 *>  21.21.21.0/24    172.16.1.2             0             0 101 i
 *>  22.22.22.22/32   172.16.1.2             0             0 101 i
 *>  31.0.0.0         172.16.1.2             0             0 101 i
 *>  33.0.0.0         172.16.1.2             0             0 101 i
 *>  44.0.0.0         172.16.1.2             0             0 101 i
 *>  192.0.2.254/24   172.16.1.2             0             0 101 i
 *>  192.0.2.50       172.16.1.2             0             0 101 i

PE 4


Note
The status is Withdraw for the exist-map EXIST-2 because the condition for advertisement has not been met. 

PE4# show ip bgp all

For address family: VPNv4 Unicast

BGP table version is 82, local router ID is 10.0.0.4

     Network          Next Hop            Metric LocPrf Weight Path
Route Distinguisher: 1:1 (default for vrf red)
 *>i 21.21.21.0/24    10.0.0.1                 0    100      0 101 i
 *>i 22.22.22.22/32   10.0.0.1                 0    100      0 101 i
 *>i 31.0.0.0         10.0.0.1                 0    100      0 101 i
 *>i 33.0.0.0         10.0.0.1                 0    100      0 101 i
 *>i 44.0.0.0         10.0.0.1                 0    100      0 101 I     <- missing 41.0.0.0/8
 *>i 192.0.2.254/24   10.0.0.1                 0    100      0 101 i
 *>i 192.0.2.50       10.0.0.1                 0    100      0 101 i


PE4# show ip bgp vpnv4 all neighbors 198.51.100.3
…
…
 For address family: VPNv4 Unicast
  Translates address family IPv4 Unicast for VRF red
  Session: 198.51.100.3
  BGP table version 48, neighbor version 48/0
  Output queue size : 0
  Index 3, Advertise bit 0
  3 update-group member
  Condition-map EXIST-1, Advertise-map ADV-1, status: Advertise
  Condition-map EXIST-2, Advertise-map ADV-2, status: Withdraw 
  Condition-map EXIST-3, Advertise-map ADV-3, status: Advertise
  Condition-map EXIST-4, Advertise-map ADV-4, status: Advertise
  Slow-peer detection is disabled
  …
…
PE4#


PE4# show ip bgp vpnv4 all update-group 
          
…
…
BGP version 4 update-group 3, external, Address Family: VPNv4 Unicast
  BGP Update version : 48/0, messages 0
  Condition-map EXIST-1, Advertise-map ADV-1, status: Advertise
  Condition-map EXIST-2, Advertise-map ADV-2, status: Withdraw
  Condition-map EXIST-3, Advertise-map ADV-3, status: Advertise
  Condition-map EXIST-4, Advertise-map ADV-4, status: Advertise
  Topology: red, highest version: 47, tail marker: 47
  Format state: Current working (OK, last not in list)
                Refresh blocked (not in list, last not in list)
  Update messages formatted 4, replicated 4, current 0, refresh 0, limit 1000
  Number of NLRIs in the update sent: max 3, min 0
  Minimum time between advertisement runs is 0 seconds
  Has 1 member:
   198.51.100.3

CE 104


Note
Prefix 44.0.0.0 is missing as 41.0.0.0/8 does not appear in PE 4 to trigger the advertisement to CE 104. The state is Withdraw. 
CE104# show ip bgp all

For address family: IPv4 Unicast

BGP table version is 45, local router ID is 198.51.100.3
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal, 
              r RIB-failure, S Stale, m multipath, b backup-path, f RT-Filter, 
              x best-external, a additional-path, c RIB-compressed, 
Origin codes: i - IGP, e - EGP, ? - incomplete
RPKI validation codes: V valid, I invalid, N Not found

     Network          Next Hop            Metric LocPrf Weight Path    
 *>  21.21.21.0/24    104.0.0.1            0 	    65000 101     i
 *>  22.22.22.22/32   104.0.0.1            0  	   65000 101     i
 *>  31.0.0.0         104.0.0.1            0  	   65000 101     i
 *>  33.0.0.0         104.0.0.1            0  	   65000 101     i
 *>  192.0.2.254/24   104.0.0.1            0      65000 101     i
 *>  192.0.2.50       104.0.0.1            0      65000 101     i

Additional References for BGP VRF-Aware Conditional Advertisement

Related Documents

Related Topic Document Title

Cisco IOS commands

Cisco IOS Master Command List, All Releases

BGP commands

Cisco IOS IP Routing: BGP Command Reference

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Feature Information for BGP VRF-Aware Conditional Advertisement

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 VRF-Aware Conditional Advertisement

Feature Name

Releases

Feature Information

BGP VRF-Aware Conditional Advertisement

The Border Gateway Protocol (BGP) VRF-Aware Conditional Advertisement feature provides additional control of the advertisement of routes and extends this control to within a virtual routing and forwarding (VRF) instance.