AS Path adding router system-as when local-as is set

[noaxispoint]

Hello,

I am unsure if I am doing this correctly. I have two ASN that I am trying to get working correctly. The default ASN set on the router is 210215 and is working correctly. However, I have a second ASN that I am trying to get routes advertising correct for.

The issue I am facing is that advertised routes appear to have ther AS210215 added to the Path Segment even though I don’t see this when doing show ip bgp neighbor x.x.x.x advertised-routes. There may be some lines that seem redundant but it is because I have been trying many things to get this working.

Below is my config which may make more sense:

set policy prefix-list 401903-IPv4-OUT description 'Subnet of 401903'
set policy prefix-list 401903-IPv4-OUT rule 10 action 'permit'
set policy prefix-list 401903-IPv4-OUT rule 10 prefix '23.143.196.0/24'
set policy prefix-list 401903-IPv4-OUT rule 500 action 'deny'
set policy prefix-list 401903-IPv4-OUT rule 500 prefix '0.0.0.0/0'
##
set policy route-map 401903-TRANSIT-OUT rule 10 action 'permit'
set policy route-map 401903-TRANSIT-OUT rule 30 match ip address prefix-list '401903-IPv4-OUT'
set policy route-map 401903-TRANSIT-OUT rule 30 set as-path exclude 'all'
set policy route-map 401903-TRANSIT-OUT rule 30 set ip-next-hop '185.44.83.179'
##
set protocols bgp neighbor 185.44.83.178 address-family ipv4-unicast as-override
set protocols bgp neighbor 185.44.83.178 address-family ipv4-unicast route-map export '401903-TRANSIT-OUT'
set protocols bgp neighbor 185.44.83.178 address-family ipv4-unicast route-map import 'DENY-ALL'
set protocols bgp neighbor 185.44.83.178 address-family ipv4-unicast soft-reconfiguration inbound
set protocols bgp neighbor 185.44.83.178 capability dynamic
set protocols bgp neighbor 185.44.83.178 description 'iFOG-XC-IPv4-401903'
set protocols bgp neighbor 185.44.83.178 disable-connected-check
set protocols bgp neighbor 185.44.83.178 graceful-restart 'enable'
set protocols bgp neighbor 185.44.83.178 interface source-interface 'eth5.40'
set protocols bgp neighbor 185.44.83.178 local-as 401903
set protocols bgp neighbor 185.44.83.178 remote-as '34927'
set protocols bgp neighbor 185.44.83.178 update-source '185.44.83.179'
##
set protocols bgp system-as '210215'

When I check to see the advertised-routes it shows the following:

vyos@fremont-fw-as210215.fremont.as210215.net:~$ show ip bgp neighbors 185.44.83.178 advertised-routes 
BGP table version is 3554501, local router ID is 65.19.155.131, vrf id 0
Default local pref 100, local AS 401903
Status codes:  s suppressed, d damped, h history, * 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
 *> 23.143.196.0/24  185.44.83.179            0         32768 i

Total number of prefixes 1

However, when I capture the packets using tcpdump I see it appears to be adding 210215. All routing for 210215 is still working fine.

Am I missing something?

[L0crian]

Yes, this is a common “gotcha” when using local-as. By default, when you use that it will append the system-as. This is a loop prevention mechanism. To get around this, update your config with this line:

set protocols bgp neighbor 185.44.83.178 local-as 401903 no-prepend replace-as

It’s important to evaluate your topology and ensure you won’t create any loops by doing this.

[noaxispoint]

Thank you very much! This appears to have solved the issue.

I shouldn’t have any loops since I am only advertising this route out via this peer.