Allowas-In

This scenario demonstrates how to configure the allowas-in feature for a BGP neighbor. By default, BGP rejects routes that contain its own AS number in the AS_PATH to prevent loops. The allowas-in feature allows a router to accept routes with its own AS in the path up to a specified number of occurrences, which is useful in hub-and-spoke eBGP topologies where the same AS may appear multiple times legitimately.

Test eBGP - Allowas-in enabled

Description

Test to verify that allowas-in allows routes with own AS in the AS_PATH. DUT0 is configured with allowas-in number 3. DUT0 should now accept the route even though it contains its own AS number.

Scenario

Step 1: Set the following configuration in DUT0 :

set interfaces ethernet eth0 address 10.10.0.100/24
set protocols bgp 100 neighbor peer allowas-in number 3
set protocols bgp 100 neighbor peer remote-address 10.10.0.200
set protocols bgp 100 neighbor peer remote-as 200
set protocols bgp 100 neighbor peer route-map export ALLOW-ALL
set protocols bgp 100 neighbor peer route-map import ALLOW-ALL
set protocols route-map ALLOW-ALL rule 10 action permit
set system login user admin authentication encrypted-password '$6$GSjsCj8gHLv$/VcqU6FLi6CT2Oxn0MJQ2C2tqnRDrYKNF8HIYWJp68nvXvPdFccDsT04.WtigUONbKYrgKg8d6rEs8PjljMkH0'

Step 2: Set the following configuration in DUT1 :

set interfaces dummy dum0 address 1.1.1.1/24
set interfaces ethernet eth0 address 10.10.0.200/24
set protocols bgp 200 neighbor peer remote-address 10.10.0.100
set protocols bgp 200 neighbor peer remote-as 100
set protocols bgp 200 neighbor peer route-map export prepend-as
set protocols bgp 200 redistribute connected
set protocols route-map prepend-as rule 10 action permit
set protocols route-map prepend-as rule 10 set as-path prepend 100
set system login user admin authentication encrypted-password '$6$GSjsCj8gHLv$/VcqU6FLi6CT2Oxn0MJQ2C2tqnRDrYKNF8HIYWJp68nvXvPdFccDsT04.WtigUONbKYrgKg8d6rEs8PjljMkH0'

Attention

Verify eBGP session establishes between DUT0 and DUT1.

Step 3: Run command protocols bgp show ip summary at DUT0 and check if output matches the following regular expressions:

10.10.0.200.*Established
Show output
IPv4 Unicast Summary:
BGP router identifier 10.10.0.100, local AS number 100 VRF default vrf-id 0
BGP table version 0
RIB entries 0, using 0 bytes of memory
Peers 1, using 24 KiB of memory

Neighbor        LocalAddr       V         AS   MsgRcvd   MsgSent   TblVer  InQ OutQ  Up/Down        State   PfxRcd   PfxSnt Desc
10.10.0.200     10.10.0.100     4        200         3         5        0    0    0 00:00:00  Established        0        0 N/A

Total number of neighbors 1

Note

With allowas-in enabled, DUT0 should accept route 1.1.1.0/24 despite containing its own AS.

Step 4: Run command protocols bgp show ip at DUT0 and check if output matches the following regular expressions:

1.1.1.0/24
Show output
BGP table version is 2, local router ID is 10.10.0.100, vrf id 0
Default local pref 100, local AS 100
local address -
Status codes:  s suppressed, d damped, h history, u unsorted, * valid, > best, = multipath,
               i internal, r RIB-failure, S Stale, R Removed
Nexthop codes: @NNN nexthop's vrf id, < announce-nh-self
Origin codes:  i - IGP, e - EGP, ? - incomplete
RPKI validation codes: V valid, I invalid, N Not found

     Network          Next Hop            Metric LocPrf Weight Path
 *u  1.1.1.0/24       10.10.0.200              0             0 200 100 ?
 *u  10.10.0.0/24     10.10.0.200              0             0 200 100 ?

Displayed 2 routes and 2 total paths

Attention

Verify the AS_PATH contains the local AS (100) prepended by DUT1.

Step 5: Run command protocols bgp show ip 1.1.1.0/24 at DUT0 and check if output matches the following regular expressions:

200 100
Show output
BGP routing table entry for 1.1.1.0/24, version 1
Paths: (1 available, best #1, table default)
  Advertised to peers:
  10.10.0.200
  200 100
    10.10.0.200 from 10.10.0.200 (10.10.0.200)
      Origin incomplete, metric 0, valid, external, best (First path received)
      Last update: Thu Mar  5 14:38:50 2026

Test eBGP - Allowas-in disabled (default)

Description

Test to verify that by default BGP rejects routes containing its own AS in the AS_PATH. DUT1 prepends DUT0’s AS (100) to the AS_PATH, simulating a route that has traversed DUT0’s AS. DUT0 should reject this route because it contains its own AS number.

Scenario

Step 1: Set the following configuration in DUT0 :

set interfaces ethernet eth0 address 10.10.0.100/24
set protocols bgp 100 neighbor peer remote-address 10.10.0.200
set protocols bgp 100 neighbor peer remote-as 200
set protocols bgp 100 neighbor peer route-map export ALLOW-ALL
set protocols bgp 100 neighbor peer route-map import ALLOW-ALL
set protocols route-map ALLOW-ALL rule 10 action permit
set system login user admin authentication encrypted-password '$6$GSjsCj8gHLv$/VcqU6FLi6CT2Oxn0MJQ2C2tqnRDrYKNF8HIYWJp68nvXvPdFccDsT04.WtigUONbKYrgKg8d6rEs8PjljMkH0'

Step 2: Set the following configuration in DUT1 :

set interfaces dummy dum0 address 1.1.1.1/24
set interfaces ethernet eth0 address 10.10.0.200/24
set protocols bgp 200 neighbor peer remote-address 10.10.0.100
set protocols bgp 200 neighbor peer remote-as 100
set protocols bgp 200 neighbor peer route-map export prepend-as
set protocols bgp 200 redistribute connected
set protocols route-map prepend-as rule 10 action permit
set protocols route-map prepend-as rule 10 set as-path prepend 100
set system login user admin authentication encrypted-password '$6$GSjsCj8gHLv$/VcqU6FLi6CT2Oxn0MJQ2C2tqnRDrYKNF8HIYWJp68nvXvPdFccDsT04.WtigUONbKYrgKg8d6rEs8PjljMkH0'

Attention

Verify eBGP session establishes between DUT0 and DUT1.

Step 3: Run command protocols bgp show ip summary at DUT0 and check if output matches the following regular expressions:

10.10.0.200.*Established
Show output
IPv4 Unicast Summary:
BGP router identifier 10.10.0.100, local AS number 100 VRF default vrf-id 0
BGP table version 0
RIB entries 0, using 0 bytes of memory
Peers 1, using 24 KiB of memory

Neighbor        LocalAddr       V         AS   MsgRcvd   MsgSent   TblVer  InQ OutQ  Up/Down        State   PfxRcd   PfxSnt Desc
10.10.0.200     10.10.0.100     4        200         3         5        0    0    0 00:00:00  Established        0        0 N/A

Total number of neighbors 1

Note

DUT0 should NOT receive route 1.1.1.0/24 because it contains its own AS (100) in the AS_PATH.

Step 4: Run command protocols bgp show ip at DUT0 and check if output does not match the following regular expressions:

1.1.1.0/24
Show output
No BGP prefixes displayed, 0 exist