Cisco NCS 5500 Series User manual

BGP Configuration Guide for Cisco NCS 5500 Series Routers, IOS XR
Release 6.2.x
First Published: 2017-07-14
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CONTENTS
Preface Preface ix
Changes to This Document ix
Obtaining Documentation and Submitting a Service Request ix
CHAPTER 1 New and Changed BGP Features 1
New and Changed BGP Features 1
CHAPTER 2 Implementing BGP 3
BGP Functional Overview 3
Enable BGP Routing 4
Adjust BGP Timers 7
Change BGP Default Local Preference Value 8
Configure MED Metric for BGP 9
Configure BGP Weights 10
Tune BGP Best-Path Calculation 11
Set BGP Administrative Distance 13
Indicate BGP Back-door Routes 14
Configure Aggregate Addresses 16
Autonomous System Number Formats in BGP 18
2-byte Autonomous System Number Format 18
4-byte Autonomous System Number Format 18
as-format Command 18
BGP Multi-Instance and Multi-AS 18
Configure Multiple BGP Instances for a Specific Autonomous System 19
BGP Routing Domain Confederation 20
Configure Routing Domain Confederation for BGP 20
BGP Additional Paths 23
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Configure BGP Additional Paths 23
BGP Maximum Prefix 25
Configure Discard Extra Paths 25
BGP Best-External Path 27
Configure Best-External Path Advertisement 28
BGP Local Label Retention 29
Retain Allocated Local Label for Primary Path 29
iBGP Multipath Load Sharing 30
Configure iBGP Multipath Load Sharing 30
Route Dampening 32
Configuring BGP Route Dampening 32
Routing Policy Enforcement 33
Apply Policy When Updating Routing Table 33
Configure BGP Neighbor Group and Neighbors 35
Disable BGP Neighbor 38
Resetting Neighbors Using BGP Inbound Soft Reset 39
Resetting Neighbors Using BGP Outbound Soft Reset 40
Reset Neighbors Using BGP Hard Reset 41
Configure Software to Store Updates from Neighbor 42
Log Neighbor Changes 43
BGP Route Reflectors 43
Configure Route Reflector for BGP 44
Configure BGP Route Filtering by Route Policy 46
Configure BGP Attribute Filtering 47
BGP Next Hop Tracking 49
Configure BGP Next-Hop Trigger Delay 49
Disable Next-Hop Processing on BGP Updates 50
BGP Cost Community 51
Configure BGP Cost Community 51
Configure BGP Community and Extended-Community Advertisements 54
Redistribute iBGP Routes into IGP 56
Redistribute IGPs to BGP 57
Update Groups 58
Monitor BGP Update Groups 59
L3VPN iBGP PE-CE 60
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Restrictions for L3VPN iBGP PE-CE 60
Configuring L3VPN iBGP PE-CE 60
Flow-tag propagation 63
Restrictions for flow-tag propagation 63
Source and destination-based flow tag 63
Configure Source and Destination-based Flow Tag 63
BGP Keychains 65
Configure Keychains for BGP 65
BGP Nonstop Routing 66
Configure BGP Nonstop Routing 66
Disable BGP Nonstop Routing 66
Re-enable BGP Nonstop Routing 67
Accumulated Interior Gateway Protocol Attribute 68
Originate Prefixes with AiGP 68
Configure BGP Accept Own 70
BGP Link-State 73
Configure BGP Link-state 74
Configure Domain Distinguisher 75
BGP Permanent Network 75
Configure BGP Permanent Network 76
Advertise Permanent Network 78
Enable BGP Unequal Cost Recursive Load Balancing 80
DMZ Link Bandwidth for Unequal Cost Recursive Load Balancing 83
Enable BGP Unequal Cost Recursive Load Balancing 84
DMZ Link Bandwidth Over EBGP Peer 87
Sending and Receiving DMZ Link Bandwidth Extended Community over eBGP
Peer 88
BGP Prefix Origin Validation Based on RPKI 90
Configure RPKI Cache-server 90
Configure RPKI Prefix Validation 93
Configure RPKI Bestpath Computation 95
Resilient Per-CE Label Allocation Mode 96
Configure Resilient Per-CE Label Allocation Mode Under VRF Address Family 96
Configure Resilient Per-CE Label Allocation Mode Using Route-Policy 98
BGP VRF Dynamic Route Leaking 100
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Configure VRF Dynamic Route Leaking 100
Configuring a VPN Routing and Forwarding Instance in BGP 102
Define Virtual Routing and Forwarding Tables in Provider Edge Routers 102
Configure Route Distinguisher 104
Configure PE-PE or PE-RR Interior BGP Sessions 106
Configure BGP as PE-CE Protocol 109
Resetting an eBGP Session Immediately Upon Link Failure 113
Selective FIB Download 114
Configuring Selective FIB Download 116
Information about Implementing BGP 117
BGP Router Identifier 118
BGP Default Limits 118
BGP Attributes and Operators 119
BGP Best Path Algorithm 130
Comparing Pairs of Paths 130
Order of Comparisons 132
Best Path Change Suppression 133
BGP Update Generation and Update Groups 133
BGP Update Group 134
BGP Cost Community Reference 134
BGP Next Hop Reference 134
BGP Nonstop Routing Reference 136
BGP Route Reflectors Reference 138
iBGP Multipath Load Sharing Reference 141
L3VPN iBGP PE-CE Reference 142
MPLS VPN Carrier Supporting Carrier 142
Per VRF and Per CE Label for IPv6 Provider Edge 143
IPv6 Unicast Routing 143
Remove and Replace Private AS Numbers from AS Path in BGP 144
BGP Update Message Error Handling 144
BGP Error Handling and Attribute Filtering Syslog Messages 145
BGP-RIB Feedback Mechanism for Update Generation 145
Use-defined Martian Check 146
CHAPTER 3 EVPN Virtual Private Wire Service (VPWS) 147
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Information About EVPN-VPWS Single Homed 147
Configuring L2VPN EVPN Address Family Under BGP 148
Configuring EVPN-VPWS 149
Configuring EVPN-VPWS: Example 151
CHAPTER 4 BGP-based VPWS Autodiscovery 153
Configuring VPWS with BGP Autodiscovery and Signaling 153
VPWS with BGP Autodiscovery and BGP Signaling 156
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Contents

Preface
The Routing Configuration Guide for Cisco NCS 5500 Series Routers preface contains these sections:
•Changes to This Document, page ix
•Obtaining Documentation and Submitting a Service Request, page ix
Changes to This Document
This table lists the technical changes made to this document since it was first released.
Table 1: Changes to This Document
SummaryDate
Initial release of this document.March 2017
Republished for Release 6.2.2July 2017
Obtaining Documentation and Submitting a Service Request
For information on obtaining documentation, using the Cisco Bug Search Tool (BST), submitting a service
request, and gathering additional information, see What's New in Cisco Product Documentation.
To receive new and revised Cisco technical content directly to your desktop, you can subscribe to the What's
New in Cisco Product Documentation RSS feed. RSS feeds are a free service.
BGP Configuration Guide for Cisco NCS 5500 Series Routers, IOS XR Release 6.2.x
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BGP Configuration Guide for Cisco NCS 5500 Series Routers, IOS XR Release 6.2.x
x
Preface
Obtaining Documentation and Submitting a Service Request

CHAPTER 1
New and Changed BGP Features
This table summarizes the new and changed feature information for the Routing Configuration Guide for
Cisco NCS 5500 Series Routers, and tells you where they are documented.
•New and Changed BGP Features, page 1
New and Changed BGP Features
This table summarizes the new and changed feature information for the Routing Configuration Guide for
Cisco NCS 5500 Series Routers, and tells you where they are documented.
Table 2: BGP Features Added or Modified in IOS XR Release 6.2.x
Where DocumentedChanged in ReleaseDescriptionFeature
DMZ Link Bandwidth Over
EBGP Peer, on page 87
Release 6.2.2The feature was introduced.DMZ Link Bandwidth
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BGP Configuration Guide for Cisco NCS 5500 Series Routers, IOS XR Release 6.2.x
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New and Changed BGP Features
New and Changed BGP Features

CHAPTER 2
Implementing BGP
Border Gateway Protocol (BGP) is an Exterior Gateway Protocol (EGP) that allows you to create loop-free
interdomain routing between autonomous systems. An autonomous system is a set of routers under a single
technical administration. Routers in an autonomous system can use multiple Interior Gateway Protocols
(IGPs) to exchange routing information inside the autonomous system and an EGP to route packets outside
the autonomous system.
This module provides conceptual and configuration information on BGP.
ModificationRelease
This feature was introduced.Release 6.0
•BGP Functional Overview, page 3
BGP Functional Overview
BGP uses TCP as its transport protocol. Two BGP routers form a TCP connection between one another (peer
routers) and exchange messages to open and confirm the connection parameters.
BGP routers exchange network reachability information. This information is mainly an indication of the full
paths (BGP autonomous system numbers) that a route should take to reach the destination network. This
information helps construct a graph that shows which autonomous systems are loop free and where routing
policies can be applied to enforce restrictions on routing behavior.
Any two routers forming a TCP connection to exchange BGP routing information are called peers or neighbors.
BGP peers initially exchange their full BGP routing tables. After this exchange, incremental updates are sent
as the routing table changes. BGP keeps a version number of the BGP table, which is the same for all of its
BGP peers. The version number changes whenever BGP updates the table due to routing information changes.
Keepalive packets are sent to ensure that the connection is alive between the BGP peers and notification
packets are sent in response to error or special conditions.
BGP Configuration Guide for Cisco NCS 5500 Series Routers, IOS XR Release 6.2.x
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Enable BGP Routing
Perform this task to enable BGP routing and establish a BGP routing process. Configuring BGP neighbors is
included as part of enabling BGP routing.
At least one neighbor and at least one address family must be configured to enable BGP routing. At least
one neighbor with both a remote AS and an address family must be configured globally using the address
family and remote as commands.
Note
Before You Begin
BGP must be able to obtain a router identifier (for example, a configured loopback address). At least, one
address family must be configured in the BGP router configuration and the same address family must also be
configured under the neighbor.
If the neighbor is configured as an external BGP (eBGP) peer, you must configure an inbound and outbound
route policy on the neighbor using the route-policy command.
Note
SUMMARY STEPS
1. configure
2. route-policy route-policy-name
3. end-policy
4. commit
5. configure
6. router bgp as-number
7. bgp router-id ip-address
8. address-family {ipv4 |ipv6 }unicast
9. exit
10. neighbor ip-address
11. remote-as as-number
12. address-family {ipv4 |ipv6 }unicast
13. route-policy route-policy-name {in |out }
14. commit
DETAILED STEPS
Step 1 configure
Step 2 route-policy route-policy-name
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Implementing BGP
Enable BGP Routing

Example:
RP/0/RP0/CPU0:router(config)# route-policy drop-as-1234
RP/0/RP0/CPU0:router(config-rpl)# if as-path passes-through '1234' then
RP/0/RP0/CPU0:router(config-rpl)# apply check-communities
RP/0/RP0/CPU0:router(config-rpl)# else
RP/0/RP0/CPU0:router(config-rpl)# pass
RP/0/RP0/CPU0:router(config-rpl)# endif
(Optional) Creates a route policy and enters route policy configuration mode, where you can define the route policy.
Step 3 end-policy
Example:
RP/0/RP0/CPU0:router(config-rpl)# end-policy
(Optional) Ends the definition of a route policy and exits route policy configuration mode.
Step 4 commit
Step 5 configure
Step 6 router bgp as-number
Example:
RP/0/RP0/CPU0:router(config)# router bgp 120
Specifies the BGP AS number and enters the BGP configuration mode, allowing you to configure the BGP routing
process.
Step 7 bgp router-id ip-address
Example:
RP/0/RP0/CPU0:router(config-bgp)# bgp router-id 192.168.70.24
Configures the local router with a specified router ID.
Step 8 address-family {ipv4 |ipv6 }unicast
Example:
RP/0/RP0/CPU0:router(config-bgp)# address-family ipv4 unicast
Specifies either the IPv4 or IPv6 address family and enters address family configuration submode.
To see a list of all the possible keywords and arguments for this command, use the CLI help (?).
Step 9 exit
Example:
RP/0/RP0/CPU0:router(config-bgp-af)# exit
Exits the current configuration mode.
Step 10 neighbor ip-address
Example:
RP/0/RP0/CPU0:router(config-bgp)# neighbor 172.168.40.24
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Implementing BGP
Enable BGP Routing

Places the router in neighbor configuration mode for BGP routing and configures the neighbor IP address as a BGP peer.
Step 11 remote-as as-number
Example:
RP/0/RP0/CPU0:router(config-bgp-nbr)# remote-as 2002
Creates a neighbor and assigns a remote autonomous system number to it.
Step 12 address-family {ipv4 |ipv6 }unicast
Example:
RP/0/RP0/CPU0:router(config-bgp-nbr)# address-family ipv4 unicast
Specifies either the IPv4 or IPv6 address family and enters address family configuration submode.
To see a list of all the possible keywords and arguments for this command, use the CLI help (?).
Step 13 route-policy route-policy-name {in |out }
Example:
RP/0/RP0/CPU0:router(config-bgp-nbr-af)# route-policy drop-as-1234 in
(Optional) Applies the specified policy to inbound IPv4 unicast routes.
Step 14 commit
Enabling BGP: Example
The following shows how to enable BGP.
prefix-set static
2020::/64,
2012::/64,
10.10.0.0/16,
10.2.0.0/24
end-set
route-policy pass-all
pass
end-policy
route-policy set_next_hop_agg_v4
set next-hop 10.0.0.1
end-policy
route-policy set_next_hop_static_v4
if (destination in static) then
set next-hop 10.1.0.1
else
drop
endif
end-policy
route-policy set_next_hop_agg_v6
set next-hop 2003::121
end-policy
route-policy set_next_hop_static_v6
if (destination in static) then
set next-hop 2011::121
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Implementing BGP
Enable BGP Routing

else
drop
endif
end-policy
router bgp 65000
bgp fast-external-fallover disable
bgp confederation peers
65001
65002
bgp confederation identifier 1
bgp router-id 1.1.1.1
address-family ipv4 unicast
aggregate-address 10.2.0.0/24 route-policy set_next_hop_agg_v4
aggregate-address 10.3.0.0/24
redistribute static route-policy set_next_hop_static_v4
address-family ipv6 unicast
aggregate-address 2012::/64 route-policy set_next_hop_agg_v6
aggregate-address 2013::/64
redistribute static route-policy set_next_hop_static_v6
neighbor 10.0.101.60
remote-as 65000
address-family ipv4 unicast
neighbor 10.0.101.61
remote-as 65000
address-family ipv4 unicast
neighbor 10.0.101.62
remote-as 3
address-family ipv4 unicast
route-policy pass-all in
route-policy pass-all out
neighbor 10.0.101.64
remote-as 5
update-source Loopback0
address-family ipv4 unicast
route-policy pass-all in
route-policy pass-all out
Adjust BGP Timers
BGP uses certain timers to control periodic activities, such as the sending of keepalive messages and the
interval after which a neighbor is assumed to be down if no messages are received from the neighbor during
the interval. The values set using the timers bgp command in router configuration mode can be overridden
on particular neighbors using the timers command in the neighbor configuration mode.
Perform this task to set the timers for BGP neighbors.
SUMMARY STEPS
1. configure
2. router bgp as-number
3. timers bgp keepalive hold-time
4. neighbor ip-address
5. timers keepalive hold-time
6. commit
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Implementing BGP
Adjust BGP Timers

DETAILED STEPS
Step 1 configure
Step 2 router bgp as-number
Example:
RP/0/RP0/CPU0:router(config)# router bgp 123
Specifies the autonomous system number and enters the BGP configuration mode, allowing you to configure the BGP
routing process.
Step 3 timers bgp keepalive hold-time
Example:
RP/0/RP0/CPU0:router(config-bgp)# timers bgp 30 90
Sets a default keepalive time and a default hold time for all neighbors.
Step 4 neighbor ip-address
Example:
RP/0/RP0/CPU0:router(config-bgp)# neighbor 172.168.40.24
Places the router in neighbor configuration mode for BGP routing and configures the neighbor IP address as a BGP peer.
Step 5 timers keepalive hold-time
Example:
RP/0/RP0/CPU0:router(config-bgp-nbr)# timers 60 220
(Optional) Sets the keepalive timer and the hold-time timer for the BGP neighbor.
Step 6 commit
Change BGP Default Local Preference Value
Perform this task to set the default local preference value for BGP paths.
SUMMARY STEPS
1. configure
2. router bgp as-number
3. bgp default local-preference value
4. commit
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Implementing BGP
Change BGP Default Local Preference Value

DETAILED STEPS
Step 1 configure
Step 2 router bgp as-number
Example:
RP/0/RP0/CPU0:router(config)# router bgp 120
Specifies the autonomous system number and enters the BGP configuration mode, allowing you to configure the BGP
routing process.
Step 3 bgp default local-preference value
Example:
RP/0/RP0/CPU0:router(config-bgp)# bgp default local-preference 200
Sets the default local preference value from the default of 100, making it either a more preferable path (over 100) or less
preferable path (under 100).
Step 4 commit
Configure MED Metric for BGP
Perform this task to set the multi exit discriminator (MED) to advertise to peers for routes that do not already
have a metric set (routes that were received with no MED attribute).
SUMMARY STEPS
1. configure
2. router bgp as-number
3. default-metric value
4. commit
DETAILED STEPS
Step 1 configure
Step 2 router bgp as-number
Example:
RP/0/RP0/CPU0:router(config)# router bgp 120
Specifies the autonomous system number and enters the BGP configuration mode, allowing you to configure the BGP
routing process.
Step 3 default-metric value
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Implementing BGP
Configure MED Metric for BGP

Example:
RP/0/RP0/CPU0:router(config-bgp)# default metric 10
Sets the default metric, which is used to set the MED to advertise to peers for routes that do not already have a metric
set (routes that were received with no MED attribute).
Step 4 commit
Configure BGP Weights
A weight is a number that you can assign to a path so that you can control the best-path selection process. If
you have particular neighbors that you want to prefer for most of your traffic, you can use the weight command
to assign a higher weight to all routes learned from that neighbor. Perform this task to assign a weight to routes
received from a neighbor.
SUMMARY STEPS
1. configure
2. router bgp as-number
3. neighbor ip-address
4. remote-as as-number
5. address-family {ipv4 |ipv6 }unicast
6. weight weight-value
7. commit
DETAILED STEPS
Step 1 configure
Step 2 router bgp as-number
Example:
RP/0/RP0/CPU0:router(config)# router bgp 120
Specifies the autonomous system number and enters the BGP configuration mode, allowing you to configure the BGP
routing process.
Step 3 neighbor ip-address
Example:
RP/0/RP0/CPU0:router(config-bgp)# neighbor 172.168.40.24
Places the router in neighbor configuration mode for BGP routing and configures the neighbor IP address as a BGP peer.
Step 4 remote-as as-number
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Implementing BGP
Configure BGP Weights