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    Example: Configuring a Local AS for EBGP Sessions

    This example shows how to configure a local autonomous system (AS) for a BGP peer so that both the global AS and the local AS are used in BGP inbound and outbound updates.

    Requirements

    No special configuration beyond device initialization is required before you configure this example.

    Overview

    Use the local-as statement when ISPs merge and want to preserve a customer’s configuration, particularly the AS with which the customer is configured to establish a peer relationship. The local-as statement simulates the AS number already in place in customer routers, even if the ISP’s router has moved to a different AS.

    This example shows how to use the local-as statement to configure a local AS. The local-as statement is supported for BGP at the global, group, and neighbor hierarchy levels.

    When you configure the local-as statement, you must specify an AS number. You can specify a number from 1 through 4,294,967,295 in plain-number format. In Junos OS Release 9.1 and later, the range for AS numbers is extended to provide BGP support for 4-byte AS numbers as defined in RFC 4893, BGP Support for Four-octet AS Number Space. In Junos OS Release 9.3 and later, you can also configure a 4-byte AS number using the AS-dot notation format of two integer values joined by a period: <16-bit high-order value in decimal>.<16-bit low-order value in decimal>. For example, the 4-byte AS number of 65,546 in plain-number format is represented as 1.10 in the AS-dot notation format. You can specify a value from 0.0 through 65535.65535 in AS-dot notation format. Junos OS continues to support 2-byte AS numbers. The 2-byte AS number range is 1 through 65,535 (this is a subset of the 4-byte range).

    Figure 1 shows the sample topology.

    Figure 1: Topology for Configuring the Local AS

    Topology for Configuring the Local AS

    In this example, Device R2 formerly belonged to AS 250 and now is in AS 200. Device R1 and Device R3 are configured to peer with AS 250 instead of with the new AS number (AS 200). Device R2 has the new AS number configured with the autonomous-system 200 statement. To enable the peering sessions to work, the local-as 250 statement is added in the BGP configuration. Because local-as 250 is configured, Device R2 includes both the global AS (200) and the local AS (250) in its BGP inbound and outbound updates.

    Configuration

    CLI Quick Configuration

    To quickly configure this example, copy the following commands, paste them into a text file, remove any line breaks, change any details necessary to match your network configuration, and then copy and paste the commands into the CLI at the [edit] hierarchy level.

    Device R1

    set interfaces fe-1/2/0 unit 1 family inet address 10.0.0.1/30set interfaces lo0 unit 1 family inet address 192.168.0.1/32set protocols bgp group ext type externalset protocols bgp group ext export send-directset protocols bgp group ext export send-staticset protocols bgp group ext peer-as 250set protocols bgp group ext neighbor 10.0.0.2set policy-options policy-statement send-direct term 1 from protocol directset policy-options policy-statement send-direct term 1 then acceptset policy-options policy-statement send-static term 1 from protocol staticset policy-options policy-statement send-static term 1 then acceptset routing-options static route 10.1.0.0/30 next-hop 10.0.0.2set routing-options autonomous-system 100

    Device R2

    set interfaces fe-1/2/0 unit 2 family inet address 10.0.0.2/30set interfaces fe-1/2/1 unit 3 family inet address 10.1.0.1/30set interfaces lo0 unit 2 family inet address 192.168.0.2/32set protocols bgp group ext type externalset protocols bgp group ext export send-directset protocols bgp group ext export send-staticset protocols bgp group ext local-as 250set protocols bgp group ext neighbor 10.0.0.1 peer-as 100set protocols bgp group ext neighbor 10.1.0.2 peer-as 300set policy-options policy-statement send-direct term 1 from protocol directset policy-options policy-statement send-direct term 1 then acceptset policy-options policy-statement send-static term 1 from protocol staticset policy-options policy-statement send-static term 1 then acceptset routing-options autonomous-system 200

    Device R3

    set interfaces fe-1/2/0 unit 4 family inet address 10.1.0.2/30set interfaces lo0 unit 3 family inet address 192.168.0.3/32set protocols bgp group ext type externalset protocols bgp group ext export send-directset protocols bgp group ext export send-staticset protocols bgp group ext peer-as 250set protocols bgp group ext neighbor 10.1.0.1set policy-options policy-statement send-direct term 1 from protocol directset policy-options policy-statement send-direct term 1 then acceptset policy-options policy-statement send-static term 1 from protocol staticset policy-options policy-statement send-static term 1 then acceptset routing-options static route 10.0.0.0/30 next-hop 10.1.0.1set routing-options autonomous-system 300

    Configuring Device R1

    Step-by-Step Procedure

    The following example requires you to navigate various levels in the configuration hierarchy. For information about navigating the CLI, see Using the CLI Editor in Configuration Mode in the Junos OS CLI User Guide .

    To configure Device R1:

    1. Configure the interfaces.
      [edit interfaces]user@R1# set fe-1/2/0 unit 1 family inet address 10.0.0.1/30
      user@R1# set lo0 unit 1 family inet address 192.168.0.1/32
    2. Configure external BGP (EBGP).
      [edit protocols bgp group ext]user@R1# set type externaluser@R1# set export send-directuser@R1# set export send-staticuser@R1# set peer-as 250user@R1# set neighbor 10.0.0.2
    3. Configure the routing policy.
      [edit policy-options]user@R1# set policy-statement send-direct term 1 from protocol directuser@R1# set policy-statement send-direct term 1 then acceptuser@R1# set policy-statement send-static term 1 from protocol staticuser@R1# set policy-statement send-static term 1 then accept
    4. Configure a static route to the remote network between Device R2 and Device R3.
      [edit routing-options]user@R1# set static route 10.1.0.0/30 next-hop 10.0.0.2
    5. Configure the global AS number.
      [edit routing-options]user@R1# set autonomous-system 100

    Results

    From configuration mode, confirm your configuration by entering the show interfaces, show policy-options, show protocols, and show routing-options commands. If the output does not display the intended configuration, repeat the instructions in this example to correct the configuration.

    user@R1# show interfacesfe-1/2/0 {unit 1 {family inet {address 10.0.0.1/30;}}}lo0 {unit 1 {family inet {address 192.168.0.1/32;}}}
    user@R1# show policy-optionspolicy-statement send-direct {term 1 {from protocol direct;then accept;}}policy-statement send-static {term 1 {from protocol static;then accept;}}
    user@R1# show protocolsbgp {group ext {type external;export [ send-direct send-static ];peer-as 250;neighbor 10.0.0.2;}}
    user@R1# show routing-optionsstatic {route 10.1.0.0/30 next-hop 10.0.0.2;}autonomous-system 100;

    When you are done configuring the device, enter commit from configuration mode.

    Configuring Device R2

    Step-by-Step Procedure

    The following example requires you to navigate various levels in the configuration hierarchy. For information about navigating the CLI, see Using the CLI Editor in Configuration Mode in the Junos OS CLI User Guide .

    To configure Device R2:

    1. Configure the interfaces.
      [edit interfaces]user@R2# set fe-1/2/0 unit 2 family inet address 10.0.0.2/30
      user@R2# set fe-1/2/1 unit 3 family inet address 10.1.0.1/30
      user@R2# set lo0 unit 2 family inet address 192.168.0.2/32
    2. Configure EBGP.
      [edit protocols bgp group ext]user@R2# set type externaluser@R2# set export send-directuser@R2# set export send-staticuser@R2# set neighbor 10.0.0.1 peer-as 100user@R2# set neighbor 10.1.0.2 peer-as 300
    3. Configure the local autonomous system (AS) number.
      [edit protocols bgp group ext]user@R2# set local-as 250
    4. Configure the global AS number.
      [edit routing-options]user@R2# set autonomous-system 200
    5. Configure the routing policy.
      [edit policy-options]user@R2# set policy-statement send-direct term 1 from protocol directuser@R2# set policy-statement send-direct term 1 then acceptuser@R2# set policy-statement send-static term 1 from protocol staticuser@R2# set policy-statement send-static term 1 then accept

    Results

    From configuration mode, confirm your configuration by entering the show interfaces, show policy-options, show protocols, and show routing-options commands. If the output does not display the intended configuration, repeat the instructions in this example to correct the configuration.

    user@R2# show interfacesfe-1/2/0 {unit 2 {family inet {address 10.0.0.2/30;}}}fe-1/2/1 {unit 3 {family inet {address 10.1.0.1/30;}}}lo0 {unit 2 {family inet {address 192.168.0.2/32;}}}
    user@R2# show policy-optionspolicy-statement send-direct {term 1 {from protocol direct;then accept;}}policy-statement send-static {term 1 {from protocol static;then accept;}}
    user@R2# show protocolsbgp {group ext {type external;export [ send-direct send-static ];local-as 250;neighbor 10.0.0.1 {peer-as 100;}neighbor 10.1.0.2 {peer-as 300;}}}
    user@R2# show routing-optionsautonomous-system 200;

    When you are done configuring the device, enter commit from configuration mode.

    Configuring Device R3

    Step-by-Step Procedure

    The following example requires you to navigate various levels in the configuration hierarchy. For information about navigating the CLI, see Using the CLI Editor in Configuration Mode in the Junos OS CLI User Guide .

    To configure Device R3:

    1. Configure the interfaces.
      [edit interfaces]user@R3# set fe-1/2/0 unit 4 family inet address 10.1.0.2/30
      user@R3# set lo0 unit 3 family inet address 192.168.0.3/32
    2. Configure EBGP.
      [edit protocols bgp group ext]user@R3# set type externaluser@R3# set export send-directuser@R3# set export send-staticuser@R3# set peer-as 250user@R3# set neighbor 10.1.0.1
    3. Configure the global autonomous system (AS) number.
      [edit routing-options]user@R3# set autonomous-system 300
    4. Configure a static route to the remote network between Device R1 and Device R2.
      [edit routing-options]user@R3# set static route 10.0.0.0/30 next-hop 10.1.0.1
    5. Configure the routing policy.
      [edit policy-options]user@R3# set policy-statement send-direct term 1 from protocol directuser@R3# set policy-statement send-direct term 1 then acceptuser@R3# set policy-statement send-static term 1 from protocol staticuser@R3# set policy-statement send-static term 1 then accept

    Results

    From configuration mode, confirm your configuration by entering the show interfaces, show policy-options, show protocols, and show routing-options commands. If the output does not display the intended configuration, repeat the instructions in this example to correct the configuration.

    user@R3# show interfacesfe-1/2/0 {unit 4 {family inet {address 10.1.0.2/30;}}}lo0 {unit 3 {family inet {address 192.168.0.3/32;}}}
    user@R3# show policy-optionspolicy-statement send-direct {term 1 {from protocol direct;then accept;}}policy-statement send-static {term 1 {from protocol static;then accept;}}
    user@R3# show protocolsbgp {group ext {type external;export [ send-direct send-static ];peer-as 250;neighbor 10.1.0.1;}}
    user@R3# show routing-optionsstatic {route 10.0.0.0/30 next-hop 10.1.0.1;}autonomous-system 300;

    When you are done configuring the device, enter commit from configuration mode.

    Verification

    Confirm that the configuration is working properly.

    Checking the Local and Global AS Settings

    Purpose

    Make sure that Device R2 has the local and global AS settings configured.

    Action

    From operational mode, enter the show bgp neighbors command.

    user@R2> show bgp neighbors
    Peer: 10.0.0.1+179 AS 100      Local: 10.0.0.2+61036 AS 250  
  Type: External    State: Established    Flags: <Sync>
  Last State: OpenConfirm   Last Event: RecvKeepAlive
  Last Error: None
  Export: [ send-direct send-static ] 
  Options: <Preference PeerAS LocalAS Refresh>
  Holdtime: 90 Preference: 170 Local AS: 250 Local System AS: 200
  Number of flaps: 0
  Peer ID: 192.168.0.1     Local ID: 192.168.0.2       Active Holdtime: 90
  Keepalive Interval: 30         Peer index: 0   
  BFD: disabled, down
  Local Interface: fe-1/2/0.2                       
  NLRI for restart configured on peer: inet-unicast
  NLRI advertised by peer: inet-unicast
  NLRI for this session: inet-unicast
  Peer supports Refresh capability (2)
  Stale routes from peer are kept for: 300
  Peer does not support Restarter functionality
  NLRI that restart is negotiated for: inet-unicast
  NLRI of received end-of-rib markers: inet-unicast
  NLRI of all end-of-rib markers sent: inet-unicast
  Peer supports 4 byte AS extension (peer-as 100)
  Peer does not support Addpath
  Table inet.0 Bit: 10000
    RIB State: BGP restart is complete
    Send state: in sync
    Active prefixes:              1
    Received prefixes:            3
    Accepted prefixes:            2
    Suppressed due to damping:    0
    Advertised prefixes:          4
  Last traffic (seconds): Received 6    Sent 14   Checked 47  
  Input messages:  Total 258    Updates 3       Refreshes 0     Octets 4969
  Output messages: Total 258    Updates 2       Refreshes 0     Octets 5037
  Output Queue[0]: 0

Peer: 10.1.0.2+179 AS 300      Local: 10.1.0.1+52296 AS 250  
  Type: External    State: Established    Flags: <Sync>
  Last State: OpenConfirm   Last Event: RecvKeepAlive
  Last Error: None
  Export: [ send-direct send-static ] 
  Options: <Preference PeerAS LocalAS Refresh>
  Holdtime: 90 Preference: 170 Local AS: 250 Local System AS: 200
  Number of flaps: 0
  Peer ID: 192.168.0.3     Local ID: 192.168.0.2       Active Holdtime: 90
  Keepalive Interval: 30         Peer index: 1   
  BFD: disabled, down
  Local Interface: fe-1/2/1.3                       
  NLRI for restart configured on peer: inet-unicast
  NLRI advertised by peer: inet-unicast
  NLRI for this session: inet-unicast
  Peer supports Refresh capability (2)
  Stale routes from peer are kept for: 300
  Peer does not support Restarter functionality
  NLRI that restart is negotiated for: inet-unicast
  NLRI of received end-of-rib markers: inet-unicast
  NLRI of all end-of-rib markers sent: inet-unicast
  Peer supports 4 byte AS extension (peer-as 300)
  Peer does not support Addpath
  Table inet.0 Bit: 10000
    RIB State: BGP restart is complete
    Send state: in sync
    Active prefixes:              1
    Received prefixes:            3
    Accepted prefixes:            2
    Suppressed due to damping:    0
    Advertised prefixes:          4
  Last traffic (seconds): Received 19   Sent 26   Checked 9   
  Input messages:  Total 256    Updates 3       Refreshes 0     Octets 4931
  Output messages: Total 256    Updates 2       Refreshes 0     Octets 4999
  Output Queue[0]: 0

    Meaning

    The Local AS: 250 and Local System AS: 200 output shows that Device R2 has the expected settings. Additionally, the output shows that the options list includes LocalAS.

    Checking the BGP Peering Sessions

    Purpose

    Ensure that the sessions are established and that the local AS number 250 is displayed.

    Action

    From operational mode, enter the show bgp summary command.

    user@R1> show bgp summary
    Groups: 1 Peers: 1 Down peers: 0
Table          Tot Paths  Act Paths Suppressed    History Damp State    Pending
inet.0                 4          2          0          0          0          0
Peer                     AS      InPkt     OutPkt    OutQ   Flaps Last Up/Dwn State|#Active/Received/Accepted/Damped...
10.0.0.2                250        232        233       0       4     1:42:37 2/4/4/0              0/0/0/0
    user@R3> show bgp summary
    Groups: 1 Peers: 1 Down peers: 0
Table          Tot Paths  Act Paths Suppressed    History Damp State    Pending
inet.0                 4          2          0          0          0          0
Peer                     AS      InPkt     OutPkt    OutQ   Flaps Last Up/Dwn State|#Active/Received/Accepted/Damped...
10.1.0.1                250        235        236       0       4     1:44:25 2/4/4/0              0/0/0/0

    Meaning

    Device R1 and Device R3 appear to be peering with a device in AS 250, even though Device R2 is actually in AS 200.

    Verifying the BGP AS Paths

    Purpose

    Make sure that the routes are in the routing tables and that the AS paths show the local AS number 250.

    Action

    From configuration mode, enter the set route protocol bgp command.

    user@R1> show route protocol bgp
    inet.0: 6 destinations, 8 routes (6 active, 0 holddown, 0 hidden)
+ = Active Route, - = Last Active, * = Both

10.0.0.0/30         [BGP/170] 01:46:44, localpref 100
                      AS path: 250 I
                    > to 10.0.0.2 via fe-1/2/0.1
10.1.0.0/30         [BGP/170] 01:46:44, localpref 100
                      AS path: 250 I
                    > to 10.0.0.2 via fe-1/2/0.1
192.168.0.2/32     *[BGP/170] 01:46:44, localpref 100
                      AS path: 250 I
                    > to 10.0.0.2 via fe-1/2/0.1
192.168.0.3/32     *[BGP/170] 01:46:40, localpref 100
                      AS path: 250 300 I
                    > to 10.0.0.2 via fe-1/2/0.1
    user@R3> show route protocol bgp
    inet.0: 6 destinations, 8 routes (6 active, 0 holddown, 0 hidden)
+ = Active Route, - = Last Active, * = Both

10.0.0.0/30         [BGP/170] 01:47:10, localpref 100
                      AS path: 250 I
                    > to 10.1.0.1 via fe-1/2/0.4
10.1.0.0/30         [BGP/170] 01:47:10, localpref 100
                      AS path: 250 I
                    > to 10.1.0.1 via fe-1/2/0.4
192.168.0.1/32     *[BGP/170] 01:47:10, localpref 100
                      AS path: 250 100 I
                    > to 10.1.0.1 via fe-1/2/0.4
192.168.0.2/32     *[BGP/170] 01:47:10, localpref 100
                      AS path: 250 I
                    > to 10.1.0.1 via fe-1/2/0.4

    Meaning

    The output shows that Device R1 and Device R3 appear to have routes with AS paths that include AS 250, even though Device R2 is actually in AS 200.

     

    Related Documentation

     

    Published: 2012-06-27

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