[c-nsp] IOS XR BGP default route - prepending AS
Brian Knight
brian.t.knight at gmail.com
Tue Apr 26 18:42:23 EDT 2016
So, I did a quick lab test, and it turns out that:
* to influence the default route attributes, one must use a route-policy
attached to the default-originate statement (as Brad mentioned)
* the output of "show bgp neighbor x.x.x.x advertise" does NOT show the
prepended AS path, but
* the receiving router DOES receive the prepended path correctly.
Lab config follows for those interested. (Routers are running IOS XRv
6.0.0 on VIRL 1.1.1.)
I'll be turning up those BGP sessions again soon, and I'll ask the remote
side if they see the path prepending.
Thanks all for your replies!
-Brian Knight
iosxr-1
-----
RP/0/0/CPU0:ios#show run
Fri Apr 22 04:56:23.042 UTC
Building configuration...
!! IOS XR Configuration 6.0.0
!! Last configuration change at Fri Apr 22 04:53:56 2016 by cisco
!
interface Loopback0
ipv4 address 53.53.53.53 255.255.255.255
!
interface MgmtEth0/0/CPU0/0
shutdown
!
interface GigabitEthernet0/0/0/0
!
interface GigabitEthernet0/0/0/0.101
ipv4 address 192.168.0.1 255.255.255.252
encapsulation dot1q 101
!
interface GigabitEthernet0/0/0/1
shutdown
!
prefix-set IPV4-DEFAULT
0.0.0.0/0
end-set
!
community-set BGP-SITECODE
53828:1003
end-set
!
route-policy IPV4-DEFAULT-DENY
if destination in IPV4-DEFAULT then
drop
else
pass
endif
end-policy
!
route-policy IPV4-BGP-NNI-DIA-IN($localpref)
apply IPV4-DEFAULT-DENY
# For primary NNIs, $localpref = 400
# For backup NNIs, $localpref = 350
#
set local-preference $localpref
set community BGP-SITECODE additive
end-policy
!
route-policy IPV4-BGP-NNI-DIA-OUT($prepend)
# For primary NNIs, $prepend = 0
# For backup NNIs, $prepend = 2
#
# Announce only default route
if destination in (0.0.0.0/0) then
prepend as-path 53828 $prepend
set community BGP-SITECODE
else
drop
endif
end-policy
!
route-policy IPV4-BGP-NNI-DIA-BACKUP-IN
apply IPV4-BGP-NNI-DIA-IN(350)
end-policy
!
route-policy IPV4-BGP-NNI-DIA-BACKUP-OUT
apply IPV4-BGP-NNI-DIA-OUT(2)
end-policy
!
route-policy IPV4-BGP-NNI-DIA-PRIMARY-IN
apply IPV4-BGP-NNI-DIA-IN(400)
end-policy
!
route-policy IPV4-BGP-NNI-DIA-PRIMARY-OUT
apply IPV4-BGP-NNI-DIA-OUT(0)
end-policy
!
route-policy IPV4-BGP-NNI-DIA-DEFAULT-BACKUP-OUT
prepend as-path 53828 2
set community BGP-SITECODE
end-policy
!
route-policy IPV4-BGP-NNI-DIA-DEFAULT-PRIMARY-OUT
set community BGP-SITECODE
end-policy
!
router bgp 53828
bgp router-id 53.53.53.53
address-family ipv4 unicast
redistribute connected
redistribute static
!
neighbor 192.168.0.2
remote-as 2828
address-family ipv4 unicast
send-community-ebgp
route-policy IPV4-BGP-NNI-DIA-BACKUP-IN in
route-policy IPV4-BGP-NNI-DIA-BACKUP-OUT out
send-extended-community-ebgp
default-originate route-policy IPV4-BGP-NNI-DIA-DEFAULT-BACKUP-OUT
soft-reconfiguration inbound
!
!
!
end
RP/0/0/CPU0:ios#sh bgp ipv4 u nei 192.168.0.2 advertised-routes
Fri Apr 22 04:56:26.072 UTC
Network Next Hop From AS Path
0.0.0.0/0 0.0.0.0 Local i
Processed 1 prefixes, 1 paths
RP/0/0/CPU0:ios#
---
iosxr-2
----
RP/0/0/CPU0:ios#show run
Fri Apr 22 04:57:57.445 UTC
Building configuration...
!! IOS XR Configuration 6.0.0
!! Last configuration change at Fri Apr 22 04:50:19 2016 by cisco
!
vrf VPN
address-family ipv4 unicast
import route-target
2828:1
!
export route-target
2828:1
!
!
!
interface Loopback0
ipv4 address 28.28.28.28 255.255.255.255
!
interface MgmtEth0/0/CPU0/0
shutdown
!
interface GigabitEthernet0/0/0/0
!
interface GigabitEthernet0/0/0/0.101
vrf VPN
ipv4 address 192.168.0.2 255.255.255.252
encapsulation dot1q 101
!
interface GigabitEthernet0/0/0/1
vrf VPN
ipv4 address 172.16.0.1 255.255.255.252
!
route-policy PERMIT-ALL
pass
end-policy
!
router static
vrf VPN
address-family ipv4 unicast
172.17.0.0/24 172.16.0.1
!
!
!
router bgp 2828
bgp router-id 28.28.28.28
address-family ipv4 unicast
redistribute connected
redistribute static
!
address-family vpnv4 unicast
!
vrf VPN
rd 2828:1
address-family ipv4 unicast
redistribute connected
redistribute static
!
neighbor 192.168.0.1
remote-as 53828
address-family ipv4 unicast
send-community-ebgp
route-policy PERMIT-ALL in
route-policy PERMIT-ALL out
send-extended-community-ebgp
soft-reconfiguration inbound
!
!
!
!
end
RP/0/0/CPU0:ios#sh bgp vrf VPN
Fri Apr 22 04:58:02.645 UTC
BGP VRF VPN, state: Active
BGP Route Distinguisher: 2828:1
VRF ID: 0x60000006
BGP router identifier 28.28.28.28, local AS number 2828
Non-stop routing is enabled
BGP table state: Active
Table ID: 0xe0000015 RD version: 7
BGP main routing table version 7
BGP NSR Initial initsync version 3 (Reached)
BGP NSR/ISSU Sync-Group versions 0/0
Status codes: s suppressed, d damped, h history, * valid, > best
i - internal, r RIB-failure, S stale, N Nexthop-discard
Origin codes: i - IGP, e - EGP, ? - incomplete
Network Next Hop Metric LocPrf Weight Path
Route Distinguisher: 2828:1 (default for vrf VPN)
*> 0.0.0.0/0 192.168.0.1 0 53828 53828
53828 i
*> 172.16.0.0/30 0.0.0.0 0 32768 ?
*> 192.168.0.0/30 0.0.0.0 0 32768 ?
Processed 3 prefixes, 3 paths
RP/0/0/CPU0:ios#sh bgp vrf VPN ipv4 u nei 192.168.0.1 routes
Fri Apr 22 04:58:05.415 UTC
BGP VRF VPN, state: Active
BGP Route Distinguisher: 2828:1
VRF ID: 0x60000006
BGP router identifier 28.28.28.28, local AS number 2828
Non-stop routing is enabled
BGP table state: Active
Table ID: 0xe0000015 RD version: 7
BGP main routing table version 7
BGP NSR Initial initsync version 3 (Reached)
BGP NSR/ISSU Sync-Group versions 0/0
Status codes: s suppressed, d damped, h history, * valid, > best
i - internal, r RIB-failure, S stale, N Nexthop-discard
Origin codes: i - IGP, e - EGP, ? - incomplete
Network Next Hop Metric LocPrf Weight Path
Route Distinguisher: 2828:1 (default for vrf VPN)
*> 0.0.0.0/0 192.168.0.1 0 53828 53828
53828 i
Processed 1 prefixes, 1 paths
RP/0/0/CPU0:ios#
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