Here’s what I’ve been able to check in the lab. The
“no-prepend” indeed removes the “local-as”-ASN from the bgp-advertisement to
another site. So this can be used to make it cleaner. Note that the real 4BASN
is never shown at the other site. You will see below that none of the other
options (replace-as, dual-as) seem to make a difference.
Setup:
(172.16.22.0/24)101RS001-----------cedge101------------mpls--------
cedge201--------------------201RS002
AS65005-----(local-as 5)AS420001111-----------------AS420002222(local-as
5)-----AS64922
I kept the ASNs on the
switches different just to be able to get the BGP info also on the switches. We
can still use the same during the migration in PROD, as they will follow the
less specific routes.
Test 1)
Cedge101#
router bgp 420001111
neighbor 172.16.20.1 local-as 5
Cedge201#
router bgp 420001111
neighbor 172.16.30.6 local-as 5
cedge101#sh ip bgp vpnv4
vrf 1 172.16.22.0/24
BGP routing table entry
for 1:1:172.16.22.0/24, version 550
Paths: (2 available, best
#1, table 1)
Not advertised to
any peer
Refresh Epoch 1
5 65005
172.16.20.1 (via vrf 1) from 172.16.20.1 (172.16.25.21)
Origin
incomplete, metric 200, localpref 100, valid, external, best
Community: 101:65005
Extended Community: RT:420001111:1
rx pathid: 0, tx pathid: 0x0
Updated on Jul 28 2021 12:22:23 UTC
Refresh Epoch 1
5 65005,
(received-only)
172.16.20.1 (via vrf 1) from 172.16.20.1 (172.16.25.21)
Origin incomplete, metric 200, localpref 100, valid, external
Community: 101:65005
rx pathid: 0, tx pathid: 0
Updated on Jul 28 2021 12:22:23 UTC
cedge201#sh ip bgp vpnv4
vrf 1 172.16.22.0/24
BGP routing table entry
for 1:1:172.16.22.0/24, version 104
Paths: (2 available, best
#1, table 1)
Advertised to
update-groups:
5
6
Refresh Epoch
1
5 65005
10.0.30.10 (via default) from 0.0.0.0 (192.168.20.2)
Origin incomplete, metric 1000, localpref 50, valid, sourced, best
Community: 101:65005
Extended Community: SoO:0:102 RT:420002222:1
rx pathid: 0, tx pathid: 0x0
Updated on Jul 28 2021 12:22:31 UTC
Refresh Epoch 1
5 65005, (received
& used)
172.16.30.2 (via vrf 1) from 172.16.30.2 (192.168.20.1)
Origin incomplete, metric 1000, localpref 50, valid, internal
Community: 101:65005
Extended Community: SoO:0:102 RT:420002222:1
rx pathid: 0, tx pathid: 0
Updated on Jul 28 2021 12:22:31 UTC
102RS001#sh ip bgp 172.16.22.0/24
BGP routing table entry
for 172.16.22.0/24, version 372
Paths: (2 available, best
#2, table default)
Advertised to
update-groups:
2
Refresh Epoch
1
5 420002222 5 65005
172.16.30.5 from 172.16.30.5 (192.168.20.2)
Origin incomplete, metric 1000, localpref 100, valid, external
Community: 6684141
Extended Community: SoO:0:102 RT:420002222:1
rx pathid: 0, tx pathid: 0
Refresh Epoch 1
5 420002222 5 65005
172.16.30.17
from 172.16.30.17 (192.168.20.1)
Origin incomplete, metric 1000, localpref 100, valid, external, best
Community: 6684141
Extended Community: SoO:0:102 RT:420002222:1
rx pathid: 0, tx pathid: 0x0
102RS001#
Test 2) no-prepend
Cedge101#
router bgp 420001111
neighbor 172.16.20.1 local-as 5 no-prepend
Cedge201#
router bgp 420001111
neighbor 172.16.30.6 local-as 5
cedge101#sh ip bgp vpnv4
vrf 1 172.16.22.0/24
BGP routing table entry
for 1:1:172.16.22.0/24, version 358
Paths: (2 available, best
#1, table 1)
Not advertised to
any peer
Refresh Epoch 1
65005
172.16.20.1 (via vrf 1) from 172.16.20.1 (172.16.25.21)
Origin
incomplete, metric 200, localpref 100, valid, external, best
Community: 101:65005
Extended Community: RT:420001111:1
rx pathid: 0, tx pathid: 0x0
Updated on Jul 28 2021 11:48:37 UTC
Refresh Epoch 1
65005,
(received-only)
172.16.20.1 (via vrf 1) from 172.16.20.1 (172.16.25.21)
Origin incomplete, metric 200, localpref 100, valid, external
Community: 101:65005
rx pathid: 0, tx pathid: 0
Updated on Jul 28 2021 11:48:37 UTC
cedge201#sh ip bgp vpnv4
vrf 1 172.16.22.0/24
BGP routing table entry
for 1:1:172.16.22.0/24, version 110
Paths: (2 available, best
#1, table 1)
Advertised to
update-groups:
5
6
Refresh Epoch
1
65005
10.0.30.10 (via default) from 0.0.0.0 (192.168.20.2)
Origin incomplete, metric 1000, localpref 50, valid,
sourced, best
Community: 101:65005
Extended Community: SoO:0:102 RT:420002222:1
rx pathid: 0, tx pathid: 0x0
Updated on Jul 28 2021 12:26:30 UTC
Refresh Epoch 1
65005, (received
& used)
172.16.30.2 (via vrf 1) from 172.16.30.2 (192.168.20.1)
Origin incomplete, metric 1000, localpref 50, valid, internal
Community: 101:65005
Extended Community: SoO:0:102 RT:420002222:1
rx pathid: 0, tx pathid: 0
Updated on Jul 28 2021 12:26:30 UTC
102RS001#sh ip bgp 172.16.22.0/24
BGP routing table entry
for 172.16.22.0/24, version 340
Paths: (2 available, best
#2, table default)
Advertised to
update-groups:
2
Refresh Epoch
1
5 420002222 65005
172.16.30.5 from 172.16.30.5 (192.168.20.2)
Origin incomplete, metric 1000, localpref 100, valid, external
Community: 6684141
Extended Community: SoO:0:102 RT:420002222:1
rx pathid: 0, tx pathid: 0
Refresh Epoch 1
5 420002222 65005
172.16.30.17
from 172.16.30.17 (192.168.20.1)
Origin incomplete, metric 1000, localpref 100, valid, external, best
Community: 6684141
Extended Community: SoO:0:102 RT:420002222:1
rx pathid: 0, tx pathid: 0x0
Test 3) no-prepend
replace-as
Cedge101#
router bgp 420001111
neighbor 172.16.20.1 local-as 5 no-prepend replace-as
Cedge201#
router bgp 420001111
neighbor 172.16.30.6 local-as 5
cedge101#sh ip bgp vpnv4
vrf 1 172.16.22.0/24
BGP routing table entry
for 1:1:172.16.22.0/24, version 578
Paths: (2 available, best
#1, table 1)
Not advertised to
any peer
Refresh Epoch 1
65005
172.16.20.1 (via vrf 1) from 172.16.20.1 (172.16.25.21)
Origin
incomplete, metric 200, localpref 100, valid, external, best
Community: 101:65005
Extended Community: RT:420001111:1
rx pathid: 0, tx pathid: 0x0
Updated on Jul 28 2021 12:28:00 UTC
Refresh Epoch 1
65005,
(received-only)
172.16.20.1 (via vrf 1) from 172.16.20.1 (172.16.25.21)
Origin incomplete, metric 200, localpref 100, valid, external
Community: 101:65005
rx pathid: 0, tx pathid: 0
Updated on Jul 28 2021 12:28:00 UTC
cedge201#sh ip bgp vpnv4
vrf 1 172.16.22.0/24
BGP routing table entry
for 1:1:172.16.22.0/24, version 126
Paths: (2 available, best
#2, table 1)
Advertised to
update-groups:
5
6
Refresh Epoch
1
65005, (received & used)
172.16.30.2 (via vrf 1) from 172.16.30.2 (192.168.20.1)
Origin incomplete, metric 1000, localpref 50, valid, internal
Community: 101:65005
Extended Community: SoO:0:102 RT:420002222:1
rx pathid: 0, tx pathid: 0
Updated on Jul 28 2021 12:28:08 UTC
Refresh Epoch 1
65005
10.0.30.10 (via default) from 0.0.0.0 (192.168.20.2)
Origin incomplete, metric 1000, localpref 50, valid, sourced, best
Community: 101:65005
Extended Community: SoO:0:102 RT:420002222:1
rx pathid: 0, tx pathid: 0x0
Updated on Jul 28 2021 12:28:08 UTC
cedge201#
102RS001#sh ip bgp 172.16.22.0/24
BGP routing table entry
for 172.16.22.0/24, version 396
Paths: (2 available, best
#2, table default)
Advertised to
update-groups:
2
Refresh Epoch
1
5 420002222 65005
172.16.30.17 from 172.16.30.17 (192.168.20.1)
Origin incomplete, metric 1000, localpref 100, valid, external
Community: 6684141
Extended Community: SoO:0:102 RT:420002222:1
rx pathid: 0, tx pathid: 0
Refresh Epoch 1
5 420002222 65005
172.16.30.5 from 172.16.30.5 (192.168.20.2)
Origin incomplete, metric 1000, localpref 100, valid, external, best
Community: 6684141
Extended Community: SoO:0:102 RT:420002222:1
rx pathid: 0, tx pathid: 0x0
Test 4) no-prepend
replace-as dual-as
Cedge101#
router bgp 420001111
neighbor 172.16.20.1 local-as 5 no-prepend replace-as dual-as
Cedge201#
router bgp 420001111
neighbor 172.16.30.6 local-as 5
cedge101#sh ip bgp vpnv4
vrf 1 172.16.22.0/24
BGP routing table entry
for 1:1:172.16.22.0/24, version 592
Paths: (2 available, best
#1, table 1)
Not advertised to
any peer
Refresh Epoch 1
65005
172.16.20.1 (via vrf 1) from 172.16.20.1 (172.16.25.21)
Origin
incomplete, metric 200, localpref 100, valid, external, best
Community: 101:65005
Extended Community: RT:420001111:1
rx pathid: 0, tx pathid: 0x0
Updated on Jul 28 2021 12:30:30 UTC
Refresh Epoch 1
65005,
(received-only)
172.16.20.1 (via vrf 1) from 172.16.20.1 (172.16.25.21)
Origin incomplete, metric 200, localpref 100, valid, external
Community: 101:65005
rx pathid: 0, tx pathid: 0
Updated on Jul 28 2021 12:30:30 UTC
cedge201#sh ip bgp vpnv4
vrf 1 172.16.22.0/24
BGP routing table entry
for 1:1:172.16.22.0/24, version 143
Paths: (2 available, best
#2, table 1)
Advertised to
update-groups:
5
6
Refresh Epoch
1
65005, (received & used)
172.16.30.2 (via vrf 1) from 172.16.30.2 (192.168.20.1)
Origin incomplete, metric 1000, localpref 50, valid, internal
Community: 101:65005
Extended Community: SoO:0:102 RT:420002222:1
rx pathid: 0, tx pathid: 0
Updated on Jul 28 2021 12:30:38 UTC
Refresh Epoch 1
65005
10.0.30.10 (via default) from 0.0.0.0 (192.168.20.2)
Origin incomplete, metric 1000, localpref 50, valid, sourced, best
Community: 101:65005
Extended Community: SoO:0:102 RT:420002222:1
rx pathid: 0, tx pathid: 0x0
Updated on Jul 28 2021 12:30:38 UTC
102RS001#sh ip bgp 172.16.22.0/24
BGP routing table entry
for 172.16.22.0/24, version 420
Paths: (2 available, best
#2, table default)
Advertised to
update-groups:
2
Refresh Epoch
1
5 420002222 65005
172.16.30.17 from 172.16.30.17 (192.168.20.1)
Origin incomplete, metric 1000, localpref 100, valid, external
Community: 6684141
Extended Community: SoO:0:102 RT:420002222:1
rx pathid: 0, tx pathid: 0
Refresh Epoch 1
5 420002222 65005
172.16.30.5 from 172.16.30.5 (192.168.20.2)
Origin incomplete, metric 1000, localpref 100, valid, external, best
Community: 6684141
Extended Community: SoO:0:102 RT:420002222:1
rx pathid: 0, tx pathid: 0x0