The site-of-origin (SoO) extended community is a BGP extended community attribute that is used to identify routes that have originated from a site so that the readvertisement of that prefix back to the source site can be prevented. The SoO extended community uniquely identifies the site from which a router has learned a route. BGP can use the SoO value associated with a route to prevent routing loops.

A route distinguisher (RD) creates routing and forwarding tables and specifies the default route distinguisher for a VPN. The RD is added to the beginning of an IPv4 prefix to change it into a globally unique VPN-IPv4 prefix. An RD can be composed in one of two ways: with an autonomous system number and an arbitrary number or with an IP address and an arbitrary number.

You can enter an RD in either of these formats:

• Enter a 16-bit autonomous system number, a colon, and a 32-bit number. For example:

45000:3

• Enter a 32-bit IP address, a colon, and a 16-bit number. For example:

192.168.10.15:1

In Cisco IOS Release 12.4(24)T, support was added for 4-byte autonomous system numbers as described in RFC 5396, Textual Representation of Autonomous System (AS) Numbers . In Cisco IOS Release 12.4(24)T, the Cisco implementation of 4-byte autonomous system numbers uses asdot notation--1.2 for example--as the only configuration format, regular expression match, and output display, with no asplain support.

In Cisco IOS Release 12.2(33)SRE, 12.2(33)XNE, and later releases, BGP support for 4-octet (4-byte) autonomous system numbers using the asplain format as the default format was introduced. The default asplain format uses decimal value numbers such as 65536, but you can configure 4-byte autonomous system numbers in both the asplain and asdot format. If you want to change the default show command output to display 4-byte autonomous system numbers in the asdot format, use the bgp asnotation dot command under router configuration mode.

For configuration examples involving 4-byte autonomous system numbers, see the Configuring a per Neighbor SoO Value with a 4-Byte AS Number Using a BGP Peer Policy Template Example or the Configuring a per Neighbor SoO Value Using a BGP neighbor Command and 4-Byte Autonomous System Numbers Example.

For more details about the Cisco implementation of BGP autonomous system number formats, see the the "Cisco BGP Overview" module.

There are three ways to configure an SoO value for a BGP neighbor:

• BGP peer policy template--A peer policy template is created, and an SoO value is configured as part of the peer policy. Under address family IPv4 VRF, a neighbor is identified and is configured to inherit the peer policy that contains the SoO value.
• BGP neighbor command--Under address family IPv4 VRF, a neighbor is identified, and an SoO value is configured for the neighbor.
• BGP peer group--Under address family IPv4 VRF, a BGP peer group is configured, an SoO value is configured for the peer group, a neighbor is identified, and the neighbor is configured as a member of the peer group.

The configuration of SoO values for BGP neighbors is performed on a provider edge (PE) router, which is the VPN entry point. When SoO is enabled, the PE router forwards prefixes to the customer premises equipment (CPE) only when the SoO tag of the prefix does not match the SoO tag configured for the CPE. For example, in the figure below, an SoO tag is set as 65000:1 for the customer site that includes routers CPE1 and CPE2 with an autonomous system number of 65000. When CPE1 sends prefixes to PE1, PE1 tags the prefixes with 65000:1, which is the SoO tag for CPE1 and CPE2. When PE1 sends the tagged prefixes to PE2, PE2 performs a match against the SoO tag from CPE2. Any prefixes with the tag value of 65000:1 are not sent to CPE2 because the SoO tag matches the SoO tag of CPE2, and a routing loop is avoided.

Figure 1

Network Diagram for SoO Example

In releases prior to Cisco IOS Release 12.4(11)T, 12.2(33)SRB, and 12.2(33)SB, the SoO extended community attribute is configured using an inbound route map that sets the SoO value during the update process. The introduction of two new commands configured in submodes under router configuration mode simplifies the SoO value configuration.

1.    enable

2.    configure terminal

3.    ip cef

4.    ip vrf vrf-name

5.    rd route-distinguisher

6.    route-target {export | both} route-target-ext-community

7.    route-target {import | both} route-target-ext-community

8.    exit

9.    interface type number

10.    ip vrf forwarding vrf-name [downstream vrf-name2]

11.    ip address ip-address mask [secondary]

12.    end

13.    show ip vrf [brief | detail | interfaces | id] [vrf-name] [output-modifiers]

Router# show ip vrf
Name                             Default RD            Interfaces
SOO_VRF                                 1:1                GE1/0/0

Perform this task on router PE1 in the figure above to configure an SoO value for a BGP neighbor at the router CPE1 in the figure above using a peer policy template. In this task, a peer policy template is created, and the SoO value is configured for the peer policy. Under address family IPv4 VRF, a neighbor is identified and is configured to inherit the peer policy that contains the SoO value.

For a configuration example involving 4-byte autonomous system numbers, see the Configuring a per Neighbor SoO Value with a 4-Byte AS Number Using a BGP Peer Policy Template Example.

Note

If a BGP peer inherits from several peer policy templates that specify different SoO values, the SoO value in the last template applied takes precedence and is applied to the peer. However, direct configuration of the SoO value on the BGP neighbor overrides any inherited template configurations of the SoO value.

• BGP Peer Policy Templates
  

1.    enable

2.    configure terminal

3.    router bgp autonomous-system-number

4.    address-family ipv4 [unicast | multicast| vrf vrf-name]

5.    neighbor {ip-address| peer-group-name} remote-as autonomous-system-number

6.    neighbor ip-address activate

7.    neighbor {ip-address| peer-group-name} soo extended-community-value

8.    end

Before You Begin

This task assumes that the task described in "Enabling Cisco Express Forwarding and Configuring VRF Instances" has been performed.

Note	A BGP peer cannot inherit from a peer policy or session template and be configured as a peer group member at the same. BGP templates and BGP peer groups are mutually exclusive.

1.    enable

2.    configure terminal

3.    router bgp autonomous-system-number

4.    address-family ipv4 [unicast | multicast| vrf vrf-name]

5.    neighbor peer-group-name peer-group

6.    neighbor {ip-address| peer-group-name} soo extended-community-value

7.    neighbor ip-address remote-as autonomous-system-number

8.    neighbor ip-address activate

9.    neighbor ip-address peer-group peer-group-name

10.    end

The following example shows how to create a peer policy template and configure an SoO value as part of the peer policy. After enabling Cisco Express Forwarding and configuring a VRF instance named SOO_VRF, a peer policy template is created and an SoO value is configured as part of the peer policy. Under address family IPv4 VRF, a neighbor is identified and configured to inherit the peer policy that contains the SoO value.

ip cef
ip vrf SOO_VRF
 rd 1:1
 route-target export 1:1
 route-target import 1:1
 exit
interface GigabitEthernet 1/0/0
 ip vrf forwarding SOO_VRF
 ip address 192.168.1.2 255.255.255.0
 exit
router bgp 50000
 template peer-policy SOO_POLICY
  soo 65000:1
  exit-peer-policy
 address-family ipv4 vrf SOO_VRF
  neighbor 192.168.1.1 remote-as 65000
  neighbor 192.168.1.1 activate
  neighbor 192.168.1.1 inherit peer-policy SOO_POLICY
  end

The following example shows how to create a peer policy template and configure an SoO value using a 4-byte autonomous system number, 1.2 in asdot format, as part of the peer policy. Under address family IPv4 VRF, a neighbor is identified and configured to inherit the peer policy that contains the SoO value. This example requires Cisco IOS Release 12.4(24)T, or a later release.

router bgp 1.2
 template peer-policy SOO_POLICY
  soo 1.2:3
  exit-peer-policy
 address-family ipv4 vrf SOO_VRF
  neighbor 192.168.3.2 remote-as 1.14
  neighbor 192.168.3.2 activate
  neighbor 192.168.3.2 inherit peer-policy SOO_POLICY
  end

The following example shows how to create a peer policy template and configure an SoO value using a 4-byte autonomous system number, 65538 in asplain format, as part of the peer policy. Under address family IPv4 VRF, a neighbor is identified and configured to inherit the peer policy that contains the SoO value. This example requires Cisco IOS Release 12.2(33)SRE, 12.2(33)XNE, or a later release.

router bgp 65538
 template peer-policy SOO_POLICY
  soo 65538:3
  exit-peer-policy
 address-family ipv4 vrf SOO_VRF
  neighbor 192.168.3.2 remote-as 65550
  neighbor 192.168.3.2 activate
  neighbor 192.168.3.2 inherit peer-policy SOO_POLICY
  end

The following example shows how to configure an SoO value for a BGP neighbor. After enabling Cisco Express Forwarding and configuring a VRF instance named SOO_VRF, a neighbor is identified under address family IPv4 VRF and an SoO value is configured for the neighbor.

ip cef
ip vrf SOO_VRF
 rd 1:1
 route-target export 1:1
 route-target import 1:1
 exit
interface GigabitEthernet 1/0/0
 ip vrf forwarding SOO_VRF
 ip address 192.168.2.2 255.255.255.0
 exit
router bgp 50000
 address-family ipv4 vrf SOO_VRF
  neighbor 192.168.2.1 remote-as 65000
  neighbor 192.168.2.1 activate
  neighbor 192.168.2.1 soo 65000:1
  end

The following example shows how to configure an SoO value for a BGP neighbor. In this example, all BGP neighbors, route targets, and SoO values use 4-byte autonomous system numbers in asplain format. After checking that CEF is enabled, a VRF instance named SOO_VRF is configured with route targets. In a BGP router session a neighbor is identified under address family IPv4 VRF, and an SoO value is configured for the neighbor. This example requires Cisco IOS Release 12.4(24)T, or a later release.

show ip cef
ip vrf SOO_VRF
 rd 100:200
 route-target export 1.14:1
 route-target import 1.14:1
 exit
interface Ethernet 1/0
 ip vrf forwarding SOO_VRF
 ip address 192.168.2.2 255.255.255.0
 exit
router bgp 1.2
 address-family ipv4 vrf SOO_VRF
  neighbor 192.168.2.1 remote-as 1.14
  neighbor 192.168.2.1 activate
  neighbor 192.168.2.1 soo 1.14:1
  end

The following example shows how to configure an SoO value for a BGP peer group. After enabling Cisco Express Forwarding and configuring a VRF instance named SOO_VRF, a BGP peer group is configured under address family IPv4 VRF, an SoO value is configured for the peer group, a neighbor is identified, and the neighbor is configured as a member of the peer group.

ip cef
ip vrf SOO_VRF
 rd 1:1
 route-target export 1:1
 route-target import 1:1
 exit
interface GigabitEthernet 1/0/0
 ip vrf forwarding SOO_VRF
 ip address 192.168.1.2 255.255.255.0
 exit
router bgp 50000
 address-family ipv4 vrf SOO_VRF
  neighbor SOO_GROUP peer-group
  neighbor SOO_GROUP soo 65000:65
  neighbor 192.168.1.1 remote-as 65000
  neighbor 192.168.1.1 activate
  neighbor 192.168.1.1 peer-group SOO_GROUP 
  end