BGP 4-Byte ASN

BGP 4-Byte autonomous system numbers (ASN) feature supports configuration of 4-byte ASN to BGP routers. This has been added as a separate capability which is enabled by default.

The figure shown below depicts the topology setup used for this configuration.

Figure 1. BGP Configuration and Testing Topology

To enable BGP in Router R1:
Execute the following commands:
- Enter the Global Configuration Mode.
```
iS5comm# configure terminal
```
- Enter the Autonomous System (AS) number in R1.
```
iS5comm(config)# as-num 100
```
- Configure the router-id in R1.
```
iS5comm(config)# router-id 12.0.0.1
```
- Enable BGP in R1 (assigning a 4-byte ASN).
```
iS5comm(config)# router bgp 100.1
```
- Configure R2 (with as-num 100.2) as external peer in R1.
```
iS5comm(config-router)# neighbor 12.0.0.2 remote-as 100.2
```
To enable BGP in Router R2:
Execute the following commands:
- Enter the Global Configuration Mode.
```
iS5comm# configure terminal
```
- Enter the Autonomous System (AS) number in R2.
```
iS5comm(config)# as-num 100
```
- Configure the router-id in R2.
```
iS5comm(config)# router-id 12.0.0.2
```
- Enable BGP in R2 (assigning a 4 byte ASN).
```
iS5comm(config)# router bgp 100.2
```
- Configure R2 (with as-num 100.1) as external peer in R1.
```
iS5comm(config-router)# neighbor 12.0.0.1 remote-as 100.1
```

Verify that the BGP session between the internal peers R1 and R2 is established, using the following show commands in R1 and R2.

Type the following:

R1: View the BGP summary information using ‘show ip bgp summary’

iS5comm# show ip bgp summary

Context Name : default

-------------

BGP router identifier is 12.0.0.1, local AS number 6553601

Forwarding State is enabled

BGP table version is 0

Neighbor   Version    AS    MsgRcvd  MsgSent   Up/Down    State/PfxRcd

---------  -------   ---    -------  -------   -------    ------------

12.0.0.2      4    6553602     2        2     00:00:00:3  Established

R2: View the bgp summary information using ‘show ip bgp summary’

iS5comm# show ip bgp summary

Context Name : default

-------------

BGP router identifier is 12.0.0.2, local AS number 6553602

Forwarding State is enabled

 BGP table version is 0

Neighbor   Version    AS    MsgRcvd  MsgSent   Up/Down    State/PfxRcd

---------  -------   ---    -------  -------   -------    ------------

12.0.0.1      4    6553601    11       11      00:00:5:5  Established

Note:

The display notation of ASN (in show commands) is in asplain format (i.e. represented by its decimal value e.g. 6553601) by default. It can be changed to Asdot format (i.e. the 4-byte ASN are represented by their decimal value e.g. 100.1)

Enabling Asdot notation in Router R1.

Type the following:

iS5comm# configure terminal

iS5comm(config)# router bgp 100.1

iS5comm(config)# bgp asnotation dot

iS5comm(config)# end

Enabling Asdot notation in Router R2.

Type the following:

iS5comm# configure terminal

iS5comm(config)# router bgp 100.2

iS5comm(config)# bgp asnotation dot

iS5comm(config)# end

R1: View the bgp summary information using ‘show ip bgp summary’

iS5comm# show ip bgp summary

Context Name : default

-------------

Forwarding State is enabled

BGP table version is 0

Neighbor   Version    AS    MsgRcvd  MsgSent   Up/Down    State/PfxRcd

---------  -------   ---    -------  -------   -------    ------------

 12.0.0.2      4      100.2    2       2       00:00:00:3  Established

R2: View the bgp summary information using ‘show ip bgp summary’

iS5comm# show ip bgp summary

Context Name : default

 -------------

BGP router identifier is 12.0.0.2, local AS number 100.2

Forwarding State is enabled

BGP table version is 0

Neighbor   Version    AS    MsgRcvd  MsgSent   Up/Down    State/PfxRcd

---------  -------   ---    -------  -------   -------    ------------

12.0.0.1      4       100.1    11       11      00:00:5:5  Established

Disabling Asdot notation in Router R1.

Type the following:

iS5comm# configure terminal

iS5comm(config)# router bgp 100.1

iS5comm(config)# no bgp asnotation dot

iS5comm(config)# exit

Disabling Asdot notation in Router R2.

Type the following:

iS5comm# configure terminal

iS5comm(config)# router bgp 100.2

iS5comm(config)# no bgp asnotation dot

iS5comm(config)# exit

R1: View the bgp summary information using ‘show ip bgp summary’

iS5comm# show ip bgp summary

Context Name : default

-------------

BGP router identifier is 12.0.0.1, local AS number 6553601Forwarding State is enabled

BGP table version is 0

Neighbor   Version    AS    MsgRcvd  MsgSent   Up/Down    State/PfxRcd

---------  -------   ---    -------  -------   -------    -----------

12.0.0.2      4     6553602    2        2      00:00:00:3  Established

R2: View the bgp summary information using ‘show ip bgp summary’

iS5comm# show ip bgp summary

Context Name : default

-------------

BGP router identifier is 12.0.0.2, local AS number 6553602Forwarding State is enabled

BGP table version is 0

Neighbor   Version    AS    MsgRcvd  MsgSent   Up/Down    State/PfxRcd

---------  -------   ---    -------  -------   -------    -----------

12.0.0.1      4     655361    11        11      00:00:5:5  Established

Note:

The 4-byte AS Number capability can be disabled only when BGP Global Admin Status is down.

Disabling 4-byte ASN capability in Router R1.

Type the following:

iS5comm# configure terminal

iS5comm(config)# do shutdown ip bgp

iS5comm(config)# no ip bgp four-byte-asn

iS5comm(config)# no shutdown ip bgp

iS5comm(config)# end

Establishing BGP session between R1 and R2.
Type the following:
- Configuring Local AS and Peer Remote AS at R1.
```
iS5comm# configure terminal
```
```
iS5comm(config)# router-id 12.0.0.1
```
```
iS5comm(config)# router bgp 100
```
- Configure the peer remote AS as AS_TRANS (23456), if and only if, the peer is 4-byte ASN enabled router and its AS number is greater than 65535. If the peer's AS number is less than or equal to 65535, the same should be configured as peer remote AS.
```
iS5comm(config-router)# neighbor 12.0.0.2 remote-as 23456
```
```
iS5comm(config-router)# end
```
- Configuring local AS and peer remote AS at R2.
```
iS5comm# configure terminal
```
```
iS5comm(config)# router-id 12.0.0.2
```
```
iS5comm(config)# router bgp 100.2
```
```
iS5comm(config-router)# neighbor 12.0.0.1 remote-as 100
```
```
iS5comm(config-router)# end
```

Verify that 4-byte ASN capability is not advertised/received in R1.

Type the following:

iS5comm# show ip bgp neighbor

BGP neighbor is 12.0.0.2, remote AS 23456, external link

BGP version 4, remote router ID 12.0.0.2

Network Address: None

BGP state = Established, up for 7 seconds, un-authenticated session

Configured BGP Maximum Prefix Limit 5000

AutomaticStart DISABLED

AutomaticStop DISABLED

DampPeer Oscillations DISABLED

DelayOpen DISABLED

Configured Connect Retry Count 5

Current Connect Retry Count 0

Default-originate : DISABLED

Peer Passive : DISABLED

Peer Status : NOT DAMPED

GateWay Address : NONE

Rcvd update before 0 secs, hold time is 90, keepalive interval is 30 secs

Neighbors Capability:

Route-Refresh: Advertised and received

Address family IPv4 Unicast: Advertised and received

AF-dependant capabilities:

Outbound Route Filter (ORF) type : (64) Address Prefix based ORF

Send-mode : not supported

Receive-mode : not supported

Received 2 messages, 0 Updates

Sent 2 messages, 0 Updates

Route refresh: Received 0, sent 0.

Minimum time between advertisement runs is 30 seconds

Connections established 1 time(s)

Local host: 12.0.0.1, Local port: 179

Foreign host: 12.0.0.2, Foreign port: 63916

Last Error: Code 0, SubCode 0.

Update Source 12.0.0.1

Next-Hop is automatic

MultiHop Status - disabled

Send-Community is standard,extended

Verify that 4-byte ASN capability is not advertised/received in R2.

Type the following:

iS5comm# show ip bgp neighbor

BGP neighbor is 12.0.0.1, remote AS 100, external link

BGP version 4, remote router ID 12.0.0.1

Network Address: None

BGP state = Established, up for 1 minute 10 seconds, un-authenticated session

Configured BGP Maximum Prefix Limit 5000

AutomaticStart DISABLED

AutomaticStop DISABLED

DampPeer Oscillations DISABLED

DelayOpen DISABLED

Configured Connect Retry Count 5

Current Connect Retry Count 0

Default-originate : DISABLED

Peer Passive : DISABLED

Peer Status : NOT DAMPED

GateWay Address : NONE

Rcvd update before 0 secs, hold time is 90, keepalive interval is 30 secs

Neighbors Capability:

Route-Refresh: Advertised and received

Address family IPv4 Unicast: Advertised and received

AF-dependant capabilities:

Outbound Route Filter (ORF) type : (64) Address Prefix based ORF

Send-mode : not supported

Receive-mode : not supported

Received 4 messages, 0 Updates

Sent 4 messages, 0 Updates

Route refresh: Received 0, sent 0.

Minimum time between advertisement runs is 30 seconds

Connections established 1 time(s)

Local host: 12.0.0.2, Local port: 63916

Foreign host: 12.0.0.1, Foreign port: 179

Last Error: Code 0, SubCode 0.

Update Source 12.0.0.2

Next-Hop is automatic

MultiHop Status - disabled

Send-Community is standard,extended