Route Refresh / Soft-reconfiguration Inbound on IOS-XR

ngull · ‎03-29-2012

This document explains behaviour of Cisco routers running IOS-XR when configuring soft-reconfiguration Inbound

Possible scenarios:

1. - When the BGP neighbour is not route refresh capable:

1.1 No soft-reconfiguration configured

1.2 Soft-reconfiguration configured

1.3 Soft-reconfiguration always configured

2. - When the BGP neighbour is route refresh capable:

2.1 No soft-reconfiguration configured

2.2 Soft-reconfiguration configured

2.3 Soft-reconfiguration always configured

Descriptions and outputs

1. - No route refresh capability:

1.1 No soft-reconfiguration configured

Route Refresh messages are not sent
IOS-XR router won’t keep a copy of the bgp routing table

#sh bgp vrf [vrf_name] neighbors [neighbour_address] detail

BGP neighbor is [neighbour_address], vrf [vrf_name]

Remote AS ###, local AS ###, external link

<snip>

Neighbor capabilities: Adv Rcvd

Route refresh: Yes No

4-byte AS: Yes No

Address family IPv4 Unicast: Yes Yes

<snip>

#show bgp vrf [vrf_name] neighbors [neighbour_address] received routes

% The 'show bgp neighbor received routes' command is only available when inbound soft reconfiguration is active.

To activate inbound soft reconfiguration, use the 'soft-reconfiguration inbound' command.

If the neighbor supports route-refresh, the 'always' option to the command must also be specified.

1.2 Soft-reconfiguration configured

Route refresh messages are not sent
IOS-XR router will keep a copy of the bgp routing table

#sh bgp vrf [vrf_name] neighbors [neighbour_address] detail

BGP neighbor is [neighbour_address], vrf GRX

Remote AS ###, local AS ###, external link

<snip>

Neighbor capabilities: Adv Rcvd

Route refresh: Yes No

4-byte AS: Yes No

Address family IPv4 Unicast: Yes Yes

<snip>

#show bgp vrf [vrf_name] neighbors [neighbour_address] received routes

BGP VRF [vrf_name], state: Active

BGP Route Distinguisher: [Route Distinguisher number]

VRF ID: [vrf_id]

BGP router identifier [router-id], local AS number [AS-number]

Non-stop routing is enabled

BGP table state: Active

Table ID: #####

BGP main routing table version ###

BGP NSR Initial initsync version 8 (Reached)

Dampening enabled

Status codes: s suppressed, d damped, h history, * valid, > best

i - internal, r RIB-failure, S stale

Origin codes: i - IGP, e - EGP, ? – incomplete

Network Next Hop Metric LocPrf Weight Path

Route Distinguisher: [RD_number] (default for vrf [vrf_name])

* 1.1.2.0/25 192.168.100.1 0 0 6774 ?

s 1.1.1.0/24 192.168.100.1 0 0 6774 ?

* 192.168.100.0/24 192.168.100.1 0 0 6774 ?

* 192.168.101.0/24 192.168.100.1 0 0 6774 ?

Processed 4 prefixes, 4 paths

1.3 Soft-reconfiguration always configured

Route refresh messages are not sent
IOS-XR router will keep a copy of the bgp routing table (there is not difference compare to scenario 1.2) the always keyword won’t make any difference because the neighbour is not route refresh capable

#sh bgp vrf [vrf_name] neighbors [neighbour_address] detail

BGP neighbor is [neighbour_address], vrf GRX

Remote AS ###, local AS ###, external link

<snip>

Neighbor capabilities: Adv Rcvd

Route refresh: Yes No

4-byte AS: Yes No

Address family IPv4 Unicast: Yes Yes

<snip>

#show bgp vrf [vrf_name] neighbors [neighbour_address] received routes

BGP VRF [vrf_name], state: Active

BGP Route Distinguisher: [Route Distinguisher number]

VRF ID: [vrf_id]

BGP router identifier [router-id], local AS number [AS-number]

Non-stop routing is enabled

BGP table state: Active

Table ID: ###########

BGP main routing table version ###

BGP NSR Initial initsync version 8 (Reached)

Dampening enabled

Status codes: s suppressed, d damped, h history, * valid, > best

i - internal, r RIB-failure, S stale

Origin codes: i - IGP, e - EGP, ? – incomplete

Network Next Hop Metric LocPrf Weight Path

Route Distinguisher: [RD_number] (default for vrf [vrf_name])

* 1.1.2.0/25 192.168.100.1 0 0 6774 ?

s 1.1.1.0/24 192.168.100.1 0 0 6774 ?

* 192.168.100.0/24 192.168.100.1 0 0 6774 ?

* 192.168.101.0/24 192.168.100.1 0 0 6774 ?

Processed 4 prefixes, 4 paths

2.- With Route refresh capability:

2.1 No soft-reconfiguration configured

Route refresh messages will be sent when needed

RP/0/RSP0/CPU0:Mar 28 22:12:59.745 UTC: bgp[1042]: [iowt] VRF [vrf_name]: [RD] send message type 128, length (incl. header) 23

RP/0/RSP0/CPU0:Mar 28 22:12:59.746 UTC: bgp[1042]: [iowt] VRF [vrf_name]: Send message dump for 192.168.100.1:

RP/0/RSP0/CPU0:Mar 28 22:12:59.747 UTC: bgp[1042]: [iowt] VRF [vrf_name]: ffff ffff ffff ffff ffff ffff ffff ffff

RP/0/RSP0/CPU0:Mar 28 22:12:59.748 UTC: bgp[1042]: [iowt] VRF [vrf_name]: 0017 8000 0100 01

IOS-XR router won’t keep a copy of the bgp routing table

#sh bgp vrf [vrf_name] neighbors [neighbour_address] detail

BGP neighbor is [neighbour_address], vrf GRX

Remote AS ###, local AS ###, external link

<snip>

Neighbor capabilities: Adv Rcvd

Route refresh: Yes Yes

4-byte AS: Yes Yes

Address family IPv4 Unicast: Yes Yes

<snip>

#show bgp vrf [vrf_name] neighbors [neighbour_address] received routes

% The 'show bgp neighbor received routes' command is only available when inbound soft reconfiguration is active.

To activate inbound soft reconfiguration, use the 'soft-reconfiguration inbound' command.

If the neighbor supports route-refresh, the 'always' option to the command must also be specified.

2.2 Soft-reconfiguration configured

Route refresh messages will be sent when needed

RP/0/RSP0/CPU0:Mar 28 22:15:59.571 UTC: bgp[1042]: [iowt] VRF [vrf_name]: [RD] send message type 128, length (incl. header) 23

RP/0/RSP0/CPU0:Mar 28 22:15:21.572 UTC: bgp[1042]: [iowt] VRF [vrf_name]: Send message dump for 192.168.100.1:

RP/0/RSP0/CPU0:Mar 28 22:15:21.573 UTC: bgp[1042]: [iowt] VRF [vrf_name]: ffff ffff ffff ffff ffff ffff ffff ffff

RP/0/RSP0/CPU0:Mar 28 22:15:21.574 UTC: bgp[1042]: [iowt] VRF [vrf_name]: 0017 8000 0100 01

IOS-XR router won’t keep a copy of the bgp routing table (this is because the BGP neighbour is route refresh capable)

#sh bgp vrf [vrf_name] neighbors [neighbour_address] detail

BGP neighbor is [neighbour_address], vrf GRX

Remote AS ###, local AS ###, external link

<snip>

Neighbor capabilities: Adv Rcvd

Route refresh: Yes Yes

4-byte AS: Yes Yes

Address family IPv4 Unicast: Yes Yes

<snip>

#show bgp vrf [vrf_name] neighbors [neighbour_address] received routes

% The 'show bgp neighbor received routes' command is only available when inbound soft reconfiguration is active.

To activate inbound soft reconfiguration, use the 'soft-reconfiguration inbound' command.

If the neighbor supports route-refresh, the 'always' option to the command must also be specified.

2.3 Soft-reconfiguration always configured

Route refresh messages are not sent
IOS-XR router will keep a copy of the bgp routing table even if the BGP neighbour is route refresh capable

#sh bgp vrf [vrf_name] neighbors [neighbour_address] detail

BGP neighbor is [neighbour_address], vrf GRX

Remote AS ###, local AS ###, external link

<snip>

Neighbor capabilities: Adv Rcvd

Route refresh: Yes Yes

4-byte AS: Yes Yes

Address family IPv4 Unicast: Yes Yes

<snip>

#show bgp vrf [vrf_name] neighbors [neighbour_address] received routes

<snip>

BGP VRF [vrf_name], state: Active

BGP Route Distinguisher: [Route Distinguisher number]

VRF ID: [vrf_id]

BGP router identifier [router-id], local AS number [AS-number]

Non-stop routing is enabled

BGP table state: Active

Table ID: ###########

BGP main routing table version ###

BGP NSR Initial initsync version 8 (Reached)

Dampening enabled

<snip>

Status codes: s suppressed, d damped, h history, * valid, > best

i - internal, r RIB-failure, S stale

Origin codes: i - IGP, e - EGP, ? – incomplete

Network Next Hop Metric LocPrf Weight Path

Route Distinguisher: [RD_number] (default for vrf [vrf_name])

* 1.1.2.0/25 192.168.100.1 0 0 6774 ?

s 1.1.1.0/24 192.168.100.1 0 0 6774 ?

* 192.168.100.0/24 192.168.100.1 0 0 6774 ?

* 192.168.101.0/24 192.168.100.1 0 0 6774 ?

Processed 4 prefixes, 4 paths

Route-Refresh capability	IOS		IOS-XR
No Route-Refresh Capable	Command	Behaviour	Command	Behaviour
	No soft-reconfiguration in configured	RR is not sent	No soft-reconfiguration in configured	RR is not sent
		No backup table		No backup table
	soft-reconfiguration in configured	RR is not sent	soft-reconfiguration in configured	RR is not sent
		Creates backup table		Creates backup table
			Soft-reconfiguration in always	RR is not sent
				Creates backup table
Route-Refresh Capable	Command	Behaviour	Command	Behaviour
	No soft-reconfiguration in configured	RR is sent	No soft-reconfiguration in configured	RR is sent
		No backup table		No backup table
	soft-reconfiguration in configured	RR is not sent	soft-reconfiguration in configured	RR is sent
		Creates backup table		No backup table
			Soft-reconfiguration in always	RR is not sent
				Creates backup table

Regards

Nelson

Nelson Gull
Network Consulting Engineer
Advanced Services SP Mobile UKI

Cisco Systems Limited
200 Longwater Avenue
Green Park
Reading
Berkshire
RG2 6GB
United Kingdom
Cisco.com

smailmilak · ‎05-05-2017

Hi Nelson,

Thank you for explaining this feature.

Do you recommend to use soft-reconfiguration on IGW (A9K RP2 with Tomahawk LC)?

We have multiple eBGP sessions and most of them are sending full BGP RT.