A detailed breakdown of the no-prepend-global-AS option for the local-AS setting in BGP on Juniper devices, showing how this mode influences AS-path prepending in both eBGP and iBGP peering. It covers configuration examples, route propagation scenarios, and illustrates how the local AS and global AS values are prepended differently depending on peer type.

Introduction

This series of techpost will provide a comprehensive overview of the various BGP local AS configuration options available on Juniper devices. Local AS is a powerful feature used in scenarios such as network migrations, mergers, and acquisitions. It enables BGP sessions to present a local AS number instead of the global AS when establishing peerings. We will detail the behavior of each configuration option, covering both the iBGP and eBGP use cases. A summary table of AS paths of all the routes after each local AS option is included for quick reference and comparison.

Five local AS options are available, each catering to a range of use cases, from seamless network migrations to complex multi-homing scenarios:

• Default
  
• Alias
  
• Private
  
• No-Prepend-Global-AS (focus of this article)
• Private No-Prepend-Global-AS

These options allow network operators to modify AS path information, influencing how routes are perceived and propagated within and beyond their autonomous system. The following sections provide an in-depth exploration of the no-prepend-global-AS option, highlighting its strengths and limitations.

No-prepend-global-AS Option

Syntax: local-as <AS-number> no-prepend-global-as

This option is used when you want the router to establish a BGP session using a different AS number but ensure that only this local AS number appears in the AS path to the external peers, not the global AS number. This is especially useful in VPN scenarios or during ISP mergers and migrations where the global AS configured on the router should be hidden from the customer or external peers. This enhances privacy and simplifies AS path policies in VPN environments.

When local-as is configured to simulate a different AS number for a BGP session, by default Junos prepends on both the global AS and the local AS in the AS path sent to the neighbors. This can make the AS path longer and cause routing issues or confusion. The no-prepend-global-as knob helps prevent this by not prepending the global AS in the AS path.

Example configuration:

protocols {
   bgp {
      group test {
         local-as 65551 no-prepend-global-as;
         neighbor <address> {
            peer-as 64501;
         }
      }
   }
}

Key behaviors:

• 1. Peer Establishment: BGP sessions use the local ASN in their OPEN message.
  
• 2. Local AS applied to eBGP peer:
  
  • Routes advertised from eBGP peers with local-as no-prepend-global-as configuration to other eBGP peers will have the global ASN and the local ASN number prepended to the AS path.
    
  • Routes advertised from eBGP-to-eBGP peer with local AS no-prepend-global-as configuration will only have the local ASN number prepended to the AS path.
    
  • Routes advertised from eBGP peer with local-as no-prepend-global-as configuration to iBGP peer will only have the local ASN number prepended to the AS path.
    
• 3. Local AS applied to iBGP peer:
  
  • Routes advertised from iBGP peers with local-as no-prepend-global-as configuration to other eBGP peers will have the global ASN and the local ASN prepended to the AS path.
    
  • Routes advertised from iBGP peers with local-as no-prepend-global-as configuration to other iBGP peers will only have the local ASN prepended to the AS path.
    
  • Routes advertised to the iBGP peer with local-as no-prepend-global-as configuration will NOT have the global ASN or the local ASN prepended to the AS path.

Scenario Overview

The primary goal of this document is to validate the behavior of the   and understand how the AS path is prepended or modified in different scenarios. It takes various route propagation scenarios into account and lists the expected AS path for each route.

AS Path Verification Points

We examine the AS path in three distinct contexts:

• 1. Show route advertising-protocol output
  Displays the AS path that will be advertised to the neighbor, including the AS numbers being prepended.

• 2. Actual BGP UPDATE message content (captured via traceoptions)
  Reflects the AS path as it appears within the real BGP UPDATE message sent to the peer.

• 3. Local routing table (RIB) representation
  Shows the AS path stored in the local routing table prior to any AS path modifications.

Capturing both the show route advertising-protocol output and the actual BGP UPDATE message allows us to identify and analyze any discrepancies between the intended advertisement and the actual message transmitted.

Topology

The example environment consists of five routers arranged in a star topology, with router R3 serving as the central node and Device Under Test (DUT). Each router’s global AS number is indicated within the square boxes. This is the base topology and currently does not show local-as configuration. The local-as configuration will be applied on R3 (DUT) towards either R1 (eBGP) or R4 (iBGP), depending on the specific example scenario. For each example, the topology will indicate where local-as is applied and how the route propagates. This topology is purposefully designed to thoroughly evaluate various route propagation behaviors and to analyze the effects of local AS configurations in each context.

Assumptions and Considerations

• R3 is the Device Under Test (DUT), and all observations are made through R3's lens.
• The local-as configuration is always applied on R3 (DUT) towards R1 for eBGP scenarios and towards R4 for iBGP scenarios.
• Local-as configuration is only applied towards one router (either R1 or R4) for a given eBGP/iBGP scenario.
• AS number 65551 refers to the Local AS, and AS number 64503 refers to the Global AS.
• The topology used in this document is only for educational purposes and should not be used as a reference for any other purpose.

Configuration: Local AS No-Prepend-Global-AS configured towards eBGP peer (R1)

R1                                      R4
[64501]                                 [64503]
(192.0.2.1/32)                          (192.0.2.4/32)
|                                       |
|  eBGP                       iBGP      |
(local-as 65551 no-prepend-global-as)   |
+-------------+           +-------------+
              |           |
              |___    ____|
               ___  R3____
               (192.0.2.3/32)
              |  [64503]  |
              |           |
              |           |
+-------------+           +-------------+
|                                        |
|  eBGP                       iBGP       |
|                                        |
(192.0.2.2/32)                          (192.0.2.5/32)
R2                                      R5
[64502]                                 [64503]

The following five example scenarios cover all the cases where local AS no-prepend-global-as configuration on an eBGP setup impacts the AS path.

Please note that “*” in below examples marks the neighbor on which R3 (DUT) has the local-as configuration applied.

Example 1: Route propagation from eBGP* (R1) to eBGP (R2)

This example describes the propagation of routes learned via eBGP from R1 to the eBGP peer R2, where R3 applies a local AS no-prepend-global-as on its eBGP session with R1. R1 advertises its loopback address 192.0.2.1/32 to R3, which then re-advertises the prefix to R2.

AS path of prefix 192.0.2.1/32 in the routing table inet.0 on R3:

RE3# run show route 192.0.2.1

inet.0: 20 destinations, 20 routes (20 active, 0 holddown, 0 hidden)
+ = Active Route, - = Last Active, * = Both

192.0.2.1/32       *[BGP/170] 00:13:51, localpref 100
                      AS path: 64501 I, validation-state: unverified
                    >  to 198.51.100.1 via ge-0/0/0.0

AS path of prefix 192.0.2.1/32 in the show route advertising-protocol output on R3:

RE3# run show route advertising-protocol bgp 198.51.100.5 192.0.2.1 detail

inet.0: 20 destinations, 20 routes (20 active, 0 holddown, 0 hidden)
* 192.0.2.1/32 (1 entry, 1 announced)
 BGP group r2 type External
     Nexthop: Self
     AS path: 65551 64501 I

AS path of prefix 192.0.2.1/32 in the BGP UPDATE message sent to R2:

BGP SEND 198.51.100.6+179 -> 198.51.100.5+50177
BGP SEND message type 2 (Update) length 56
BGP SEND Update PDU length 56
BGP SEND flags 0x40 code Origin(1): IGP, length(1)
BGP SEND flags 0x40 code ASPath(2) (4-byte-cap) length 14: 64503 65551 64501
BGP SEND flags 0x40 code NextHop(3): 198.51.100.6 length(4)
End-of-Attributes
BGP SEND         192.0.2.1/32

Example 2: Route propagation from eBGP* (R1) to iBGP (R4)

This example describes the propagation of routes learned via eBGP from R1 to the iBGP peer R4, where R3 applies a local AS no-prepend-global-as on its eBGP session with R1. R1 advertises its loopback address 192.0.2.1/32 to R3, which then re-advertises the prefix to R4.

AS path of prefix 192.0.2.1/32 in the routing table inet.0 on R3:

RE3# run show route 192.0.2.1

inet.0: 20 destinations, 20 routes (20 active, 0 holddown, 0 hidden)
+ = Active Route, - = Last Active, * = Both

192.0.2.1/32       *[BGP/170] 00:13:51, localpref 100
                      AS path: 64501 I, validation-state: unverified
                    >  to 198.51.100.1 via ge-0/0/0.0

AS path of prefix 192.0.2.1/32 in the show route advertising-protocol output on R3:

RE3# run show route advertising-protocol bgp 203.0.113.1 192.0.2.1 detail

inet.0: 20 destinations, 20 routes (20 active, 0 holddown, 0 hidden)
* 192.0.2.1/32 (1 entry, 1 announced)
 BGP group r4 type Internal
     Nexthop: Self
     Flags: Nexthop Change
     Localpref: 100
     AS path: 65551 64501 I

AS path of prefix 192.0.2.1/32 in the BGP UPDATE message sent to R4:

BGP SEND 203.0.113.2+179 -> 203.0.113.1+60510
BGP SEND message type 2 (Update) length 59
BGP SEND Update PDU length 59
BGP SEND flags 0x40 code Origin(1): IGP, length(1)
BGP SEND flags 0x40 code ASPath(2) (4-byte-cap) length 10: 65551 64501
BGP SEND flags 0x40 code NextHop(3): 203.0.113.2 length(4)
BGP SEND flags 0x40 code LocalPref(5): 100 length(4)
End-of-Attributes
BGP SEND         192.0.2.1/32

Example 3: Route propagation from DUT (R3) to eBGP* (R1)

This example examines the AS path of a direct/static route advertised to an eBGP peer. R3 advertises its loopback address 192.0.2.3/32 to R1.

AS path of prefix 192.0.2.3/32 in the routing table inet.0 on R3:

RE3# run show route 192.0.2.3 detail

inet.0: 20 destinations, 20 routes (20 active, 0 holddown, 0 hidden)
192.0.2.3/32 (1 entry, 1 announced)
        *Direct Preference: 0
                Next hop type: Interface, Next hop index: 0
                Address: 0x825c314
                Next-hop reference count: 1
                Kernel Table Id: 0
                Next hop: via lo0.0, selected
                State: <Active Int>
                Local AS: 64503
                Age: 27:40
                Validation State: unverified
                Task: IF
                Announcement bits (1): 3-Resolve tree 1
                AS path: I
                Thread: junos-main

The AS path of prefix 192.0.2.3/32, as shown in the output of the show route advertising-protocol command on R3:

RE3# run show route advertising-protocol bgp 198.51.100.1 192.0.2.3 detail

inet.0: 20 destinations, 20 routes (20 active, 0 holddown, 0 hidden)
* 192.0.2.3/32 (1 entry, 1 announced)
 BGP group r1 type External
     Nexthop: Self
     AS path: [65551] I

The example above includes square brackets to indicate the AS number being prepended to the AS path before advertisement

AS path of prefix 192.0.2.1/32 in the BGP UPDATE message sent to R1:

BGP SEND 198.51.100.2+60236 -> 198.51.100.1+179
BGP SEND message type 2 (Update) length 48
BGP SEND Update PDU length 48
BGP SEND flags 0x40 code Origin(1): IGP, length(1)
BGP SEND flags 0x40 code ASPath(2) (4-byte-cap) length 6: 65551
BGP SEND flags 0x40 code NextHop(3): 198.51.100.2 length(4)
End-of-Attributes
BGP SEND         192.0.2.3/32

Example 4: Route propagation from eBGP (R2) to eBGP* (R1)

This example describes the propagation of routes learned via eBGP from R2 to the eBGP peer R1, where R3 applies a local AS no-prepend-global-as on its eBGP session with R1. R2 advertises its loopback address 192.0.2.2/32 to R3, which then re-advertises the prefix to R1.

AS path of prefix 192.0.2.2/32 in the routing table inet.0 on R3:

RE3# run show route 192.0.2.2

inet.0: 20 destinations, 20 routes (20 active, 0 holddown, 0 hidden)
+ = Active Route, - = Last Active, * = Both

192.0.2.2/32       *[BGP/170] 00:00:42, localpref 100
                      AS path: 64502 I, validation-state: unverified
                    >  to 198.51.100.5 via ge-0/0/2.0

AS path of prefix 192.0.2.2/32 in the show route advertising-protocol output on R3:

RE3# run show route advertising-protocol bgp 198.51.100.1 192.0.2.2 detail

inet.0: 20 destinations, 20 routes (20 active, 0 holddown, 0 hidden)
* 192.0.2.2/32 (1 entry, 1 announced)
 BGP group r1 type External
     Nexthop: Self
     AS path: 64502 I

AS path of prefix 192.0.2.2/32 in the BGP UPDATE message sent to R1:

BGP SEND 198.51.100.2+57386 -> 198.51.100.1+179
BGP SEND message type 2 (Update) length 52
BGP SEND Update PDU length 52
BGP SEND flags 0x40 code Origin(1): IGP, length(1)
BGP SEND flags 0x40 code ASPath(2) (4-byte-cap) length 10: 65551 64502
BGP SEND flags 0x40 code NextHop(3): 198.51.100.2 length(4)
End-of-Attributes
BGP SEND         192.0.2.2/32

Example 5: Route propagation from iBGP (R4) to eBGP* (R1)

This example describes the propagation of routes learned via iBGP from R4 to the eBGP peer R1, where R3 applies a local AS no-prepend-global-as on its eBGP session with R1. R4 advertises its loopback address 192.0.2.4/32 to R3, which then re-advertises the prefix to R1.

AS path of prefix 192.0.2.4/32 in the routing table inet.0 on R3:

RE3# run show route 192.0.2.4

inet.0: 20 destinations, 20 routes (20 active, 0 holddown, 0 hidden)
+ = Active Route, - = Last Active, * = Both

192.0.2.4/32       *[BGP/170] 00:01:09, localpref 100
                      AS path: I, validation-state: unverified
                    >  to 203.0.113.1 via ge-0/0/4.0

AS path of prefix 192.0.2.4/32 in the show route advertising-protocol output on R3:

RE3# run show route advertising-protocol bgp 198.51.100.1 192.0.2.4 detail

inet.0: 20 destinations, 20 routes (20 active, 0 holddown, 0 hidden)
* 192.0.2.4/32 (1 entry, 1 announced)
 BGP group r1 type External
     Nexthop: Self
     AS path: I

AS path of prefix 192.0.2.4/32 in the BGP UPDATE message sent to R1:

BGP SEND 198.51.100.2+60321 -> 198.51.100.1+179
BGP SEND message type 2 (Update) length 48
BGP SEND Update PDU length 48
BGP SEND flags 0x40 code Origin(1): IGP, length(1)
BGP SEND flags 0x40 code ASPath(2) (4-byte-cap) length 6: 65551
BGP SEND flags 0x40 code NextHop(3): 198.51.100.2 length(4)
End-of-Attributes
BGP SEND         192.0.2.4/32

No-Prepend-Global-AS local AS Option Behavior for an eBGP Peer

Configuration: Local AS configured towards iBGP peer (R1)

R1                                      R4
[64501]                                 [64503]
(192.0.2.1/32)                          (192.0.2.4/32)
|                                       |
|  eBGP                       iBGP      |
|                              (local-as 65551 no-prepend-global-as)
+-------------+           +-------------+
              |           |
              |___    ____|
               ___  R3____
               (192.0.2.3/32)
              |  [64503]  |
              |           |
              |           |
+-------------+           +-------------+
|                                        |
|  eBGP                       iBGP       |
|                                        |
(192.0.2.2/32)                          (192.0.2.5/32)
R2                                      R5
[64502]                                 [64503]

The following five example scenarios cover all the cases where local AS no-prepend-global-as configuration on an iBGP setup impacts the AS path.

Example 1: Route propagation from iBGP* (R4) to eBGP (R1)

This example describes the propagation of routes learned via iBGP from R4 to the eBGP peer R1, where R3 applies a local AS no-prepend-global-as on its iBGP session with R4. R4 advertises its loopback address 192.0.2.4/32 to R3, which then re-advertises the prefix to R1.

AS path of prefix 192.0.2.4/32 in the routing table inet.0 on R3:

RE3# run show route 192.0.2.4

inet.0: 20 destinations, 20 routes (20 active, 0 holddown, 0 hidden)
+ = Active Route, - = Last Active, * = Both

192.0.2.4/32       *[BGP/170] 00:01:12, localpref 100
                      AS path: I, validation-state: unverified
                    >  to 203.0.113.1 via ge-0/0/4.0

AS path of prefix 192.0.2.4/32 in the show route advertising-protocol output on R3:

RE3# run show route advertising-protocol bgp 198.51.100.1 192.0.2.4 detail

inet.0: 20 destinations, 20 routes (20 active, 0 holddown, 0 hidden)
* 192.0.2.4/32 (1 entry, 1 announced)
 BGP group r1 type External
     Nexthop: Self
     AS path: 65551 I

AS path of prefix 192.0.2.4/32 as seen in the BGP UPDATE message sent to R1:

BGP SEND 198.51.100.2+58255 -> 198.51.100.1+179
BGP SEND message type 2 (Update) length 52
BGP SEND Update PDU length 52
BGP SEND flags 0x40 code Origin(1): IGP, length(1)
BGP SEND flags 0x40 code ASPath(2) (4-byte-cap) length 10: 64503 65551
BGP SEND flags 0x40 code NextHop(3): 198.51.100.2 length(4)
End-of-Attributes
BGP SEND         192.0.2.4/32

Example 2: Route propagation from iBGP* (R4) to iBGP (R5)

This example describes the propagation of routes learned via iBGP from R4 to the iBGP peer R5, where R3 applies a local AS no-prepend-global-as on its iBGP session with R4. R4 advertises its loopback address 192.0.2.4/32 to R3, which then re-advertises the prefix to R5.

AS path of prefix 192.0.2.4/32 in the routing table inet.0 on R3:

RE3# run show route 192.0.2.4

inet.0: 20 destinations, 20 routes (20 active, 0 holddown, 0 hidden)
+ = Active Route, - = Last Active, * = Both

192.0.2.4/32       *[BGP/170] 00:01:12, localpref 100
                      AS path: I, validation-state: unverified
                    >  to 203.0.113.1 via ge-0/0/4.0

AS path of prefix 192.0.2.4/32 in the show route advertising-protocol output on R3:

RE3# run show route advertising-protocol bgp 203.0.113.5 192.0.2.4 detail

inet.0: 20 destinations, 20 routes (20 active, 0 holddown, 0 hidden)
* 192.0.2.4/32 (1 entry, 1 announced)
 BGP group r5 type Internal
     Nexthop: Self
     Flags: Nexthop Change
     Localpref: 100
     AS path: 65551 I
     Cluster ID: 192.0.2.3
     Originator ID: 192.0.2.4

AS path of prefix as seen in the BGP UPDATE message sent to R5:

BGP SEND 203.0.113.6+179 -> 203.0.113.5+63772
BGP SEND message type 2 (Update) length 69
BGP SEND Update PDU length 69
BGP SEND flags 0x40 code Origin(1): IGP, length(1)
BGP SEND flags 0x40 code ASPath(2) (4-byte-cap) length 6: 65551
BGP SEND flags 0x40 code NextHop(3): 203.0.113.6 length(4)
BGP SEND flags 0x40 code LocalPref(5): 100 length(4)
BGP SEND flags 0x80 code Originator_Id(9) 192.0.2.4 length(4)
BGP SEND flags 0x80 code Cluster_List(10): length(4) 192.0.2.3
End-of-Attributes
BGP SEND         192.0.2.4/32

Example 3: Route propagation from DUT (R3) to iBGP* (R4)

This example examines the AS path of a direct/static route advertised to an iBGP peer. R3 advertises its loopback address 192.0.2.3/32 to R4.

AS path of prefix 192.0.2.3/32 in the routing table inet.0 on R3:

RE3# run show route 192.0.2.3 detail

inet.0: 20 destinations, 20 routes (20 active, 0 holddown, 0 hidden)
192.0.2.3/32 (1 entry, 1 announced)
        *Direct Preference: 0
                Next hop type: Interface, Next hop index: 0
                Address: 0x825c314
                Next-hop reference count: 1
                Kernel Table Id: 0
                Next hop: via lo0.0, selected
                State: <Active Int>
                Local AS: 64503
                Age: 50:21
                Validation State: unverified
                Task: IF
                Announcement bits (1): 3-Resolve tree 1
                AS path: I
                Thread: junos-main

AS path of prefix 192.0.2.3/32 in the show route advertising-protocol output on R3:

RE3# run show route advertising-protocol bgp 203.0.113.1 192.0.2.3 detail

inet.0: 20 destinations, 20 routes (20 active, 0 holddown, 0 hidden)
* 192.0.2.3/32 (1 entry, 1 announced)
 BGP group r4 type Internal
     Nexthop: Self
     Localpref: 100
     AS path: [65551] I

AS path of prefix 192.0.2.3/32 as seen in the BGP UPDATE message sent to R4:

BGP SEND 203.0.113.2+179 -> 203.0.113.1+56638
BGP SEND message type 2 (Update) length 49
BGP SEND Update PDU length 49
BGP SEND flags 0x40 code Origin(1): IGP, length(1)
BGP SEND flags 0x40 code ASPath(2) (4-byte-cap) length 0: <null>
BGP SEND flags 0x40 code NextHop(3): 203.0.113.2 length(4)
BGP SEND flags 0x40 code LocalPref(5): 100 length(4)
End-of-Attributes
BGP SEND         192.0.2.3/32

Example 4: Route propagation from eBGP (R1) to iBGP* (R4)

This example describes the propagation of routes learned via eBGP from R1 to the iBGP peer R4, where R3 applies a local AS no-prepend-global-as on its iBGP session with R4. R1 advertises its loopback address 192.0.2.1/32 to R3, which then re-advertises the prefix to R4.

AS path of prefix 192.0.2.1/32 in the routing table inet.0 on R3:

RE3# run show route 192.0.2.1

inet.0: 20 destinations, 20 routes (20 active, 0 holddown, 0 hidden)
+ = Active Route, - = Last Active, * = Both

192.0.2.1/32       *[BGP/170] 00:01:51, localpref 100
                      AS path: 64501 I, validation-state: unverified
                    >  to 198.51.100.1 via ge-0/0/0.0

AS path of prefix 192.0.2.1/32 in the show route advertising-protocol output on R3:

RE3# run show route advertising-protocol bgp 203.0.113.1 192.0.2.1 detail

inet.0: 20 destinations, 20 routes (20 active, 0 holddown, 0 hidden)
* 192.0.2.1/32 (1 entry, 1 announced)
 BGP group r4 type Internal
     Nexthop: Self
     Flags: Nexthop Change
     Localpref: 100
     AS path: 64501 I

AS path of prefix 192.0.2.1/32 as seen in the BGP UPDATE message sent to R4:

BGP SEND 203.0.113.2+179 -> 203.0.113.1+64431
BGP SEND message type 2 (Update) length 55
BGP SEND Update PDU length 55
BGP SEND flags 0x40 code Origin(1): IGP, length(1)
BGP SEND flags 0x40 code ASPath(2) (4-byte-cap) length 6: 64501
BGP SEND flags 0x40 code NextHop(3): 203.0.113.2 length(4)
BGP SEND flags 0x40 code LocalPref(5): 100 length(4)
End-of-Attributes
BGP SEND         192.0.2.1/32

Example 5: Route propagation from iBGP (R5) to iBGP* (R4)

This example describes the propagation of routes learned via iBGP from R5 to the iBGP peer R4, where R3 applies a local AS no-prepend-global-as on its iBGP session with R4. R5 advertises its loopback address 192.0.2.5/32 to R3, which then re-advertises the prefix to R4.

AS path of prefix 192.0.2.5/32 in the routing table inet.0 on R3:

RE3# run show route 192.0.2.5

inet.0: 20 destinations, 20 routes (20 active, 0 holddown, 0 hidden)
+ = Active Route, - = Last Active, * = Both

192.0.2.5/32       *[BGP/170] 00:00:45, localpref 100
                      AS path: I, validation-state: unverified
                    >  to 203.0.113.5 via ge-0/0/6.0

AS path of prefix 192.0.2.5/32 in the show route advertising-protocol output on R3:

RE3# run show route advertising-protocol bgp 203.0.113.1 192.0.2.5 detail

inet.0: 20 destinations, 20 routes (20 active, 0 holddown, 0 hidden)
* 192.0.2.5/32 (1 entry, 1 announced)
 BGP group r4 type Internal
     Nexthop: Self
     Flags: Nexthop Change
     Localpref: 100
     AS path: I
     Cluster ID: 192.0.2.3
     Originator ID: 192.0.2.5

AS path of prefix 192.0.2.5/32 as seen in the BGP UDPATE message sent to R4:

BGP SEND 203.0.113.2+179 -> 203.0.113.1+62963
BGP SEND message type 2 (Update) length 63
BGP SEND Update PDU length 63
BGP SEND flags 0x40 code Origin(1): IGP, length(1)
BGP SEND flags 0x40 code ASPath(2) (4-byte-cap) length 0: <null>
BGP SEND flags 0x40 code NextHop(3): 203.0.113.2 length(4)
BGP SEND flags 0x40 code LocalPref(5): 100 length(4)
BGP SEND flags 0x80 code Originator_Id(9) 192.0.2.5 length(4)
BGP SEND flags 0x80 code Cluster_List(10): length(4) 192.0.2.3
End-of-Attributes
BGP SEND         192.0.2.5/32

No-Prepend-Global-AS local AS Option Behavior for an iBGP Peer

Conclusion

This article covered the details of No-Prepend-Global-AS Local AS option, please check the articles in the section below for the other options.

Useful links

Local-AS options articles:

• Default
  
• Alias
  
• Private
  
• No-Prepend-Global-AS
• Private No-Prepend-Global-AS

Glossary

• AS(N): Autonomous System (Number)
• BGP: Border Gateway Protocol
• DUT: Device Under Test
• ISP: Internet Service Provider
• RIB: Routing Information Base