Cisco IOS XRConfig503 downloads

BGP Advanced Configuration — Cisco IOS XR

Generate carrier-grade BGP configurations for Cisco IOS XR (ASR 9000, Cisco 8000, NCS) using RPL route-policies, neighbor-groups, session-groups, and graceful maintenance.

↓ example.txt

What is it?

IOS XR BGP runs on Cisco Service Provider platforms (ASR 9000, Cisco 8000, NCS series) and is purpose-built for carrier-grade scale supporting millions of BGP prefixes (Internet full table). The fundamental architectural difference from IOS/IOS-XE is the Routing Policy Language (RPL): ALL neighbor inbound and outbound policies MUST use 'route-policy' — prefix-lists and community-lists cannot be applied directly to neighbors. RPL policies support if/elseif/else/endif logic, parameterized policies (pass a community or prefix-set as argument), and inline match operations against prefix-sets, community-sets, as-path-sets, and extcommunity-sets. Session-groups provide session-level reuse (remote-as, update-source, timers) and neighbor-groups provide full config reuse (session + policy) — equivalent to NX-OS peer templates but more structured. IOS XR requires 'commit' to activate any staged configuration, which acts as a transactional boundary for safe config changes. IOS XR also supports 'graceful-maintenance' for traffic draining before planned maintenance windows, a feature not available in IOS/IOS-XE.

When to use

·Service provider core and edge routing (AS border routers, Internet exchange points)
·Carrying Internet full routing table (800K+ prefixes) — IOS XR handles this at scale
·When advanced RPL policy logic is needed (conditional matching, parameterized policies)
·MPLS L3VPN PE routers requiring BGP VPNv4/VPNv6 with route distinguishers and targets
·Graceful maintenance scenarios requiring controlled traffic drain before router reload
·Multi-AS backbone designs with confederations and complex policy requirements
·When operational consistency across large teams requires structured, modular policy definitions

When NOT to use

·Enterprise campus deployments — use Cisco IOS/IOS-XE which is simpler to operate
·Data center deployments — use NX-OS which has better EVPN/VXLAN integration
·When operators are unfamiliar with RPL — there is significant learning curve vs IOS route-maps
·Small BGP deployments where neighbor-group/session-group overhead adds complexity

How it compares

vs Cisco IOS BGPIOS XR requires RPL route-policies for all neighbor policies (no direct prefix-list/community-list on neighbors). IOS XR has neighbor-groups vs IOS peer-groups. IOS XR requires 'commit' to activate config. IOS XR has graceful-maintenance; IOS does not.

vs Cisco NX-OS BGPNX-OS uses peer templates (session + policy) and supports route-maps. IOS XR uses session-groups/neighbor-groups and requires RPL. IOS XR is SP-focused (MPLS, Internet scale); NX-OS is DC-focused (EVPN, VXLAN).

vs Juniper Junos BGPBoth IOS XR and Junos are SP-grade. Junos uses 'policy-statement' (similar to RPL) and 'groups' (similar to neighbor-groups). IOS XR's RPL is more powerful for complex conditionals; Junos is often preferred for its configuration hierarchy clarity.

Prerequisites

→IOS XR uses two-stage commit — all config is staged and requires 'commit' to activate
→Route-policies (RPL) must exist before referencing them in neighbor-groups or neighbors
→Prefix-sets, community-sets, as-path-sets defined before referencing in route-policies
→For 'ibgp policy out enforce-modifications': required when modifying LOCAL_PREF or NEXT_HOP on iBGP egress (normally prohibited per RFC 4271)
→Loopback interfaces up and reachable via IGP before configuring iBGP with loopback update-source
→BFD configured on the interface ('bfd minimum-interval X' / 'bfd multiplier N') before enabling bfd fast-detect on BGP neighbors

Config Generator

Router Hostname *

Local AS Number *

BGP Router ID *

AS-Path Multipath Relax

Compare Router-ID for identical paths

Always Compare MED (bgp bestpath med always)

MED Confederation: treat missing MED as worst

Route Reflector Cluster ID

Confederation Identifier

Confederation Peers

Keepalive Timer (seconds)

Hold Time (seconds)

BGP Graceful Restart

Stale Path Timer (seconds)

Max eBGP Paths (ECMP)

Max iBGP Paths (ECMP)

ibgp policy out enforce-modifications

Required when modifying LOCAL_PREF or NEXT_HOP on iBGP egress — normally prohibited per RFC

Prefix Sets

Community Sets

AS-Path Sets

Route Policies (RPL)

Session Groups

Neighbor Groups

BGP Neighbors

Networks to Advertise

Aggregate Addresses

Redistribute OSPF

OSPF Process ID

OSPF Redistribution Route-Policy

Redistribute Static

Static Redistribution Route-Policy

Redistribute Connected

Connected Redistribution Route-Policy

Verification commands

show bgp summary

Overview of all BGP neighbors and prefix counts — IOS XR does not use 'ip' prefix

ExpectedState shows numeric prefix count for Established sessions; Idle/Active/Connect indicate issues

show bgp neighbors X.X.X.X

Detailed neighbor state, capabilities, timers, and policy information

ExpectedBGP state: Established, shows neighbor-group inherited from, policy names applied

show bgp ipv4 unicast

Full BGP table for IPv4 unicast

ExpectedBest paths marked >, valid *, locally originated i

show bgp ipv4 unicast X.X.X.X

Detailed path attributes for a specific prefix

ExpectedAll paths with LOCAL_PREF, AS-PATH, NEXT_HOP, MED, origin for best-path analysis

show bgp ipv4 unicast neighbors X.X.X.X advertised-routes

Routes being advertised to neighbor after outbound route-policy

ExpectedPrefix list — compare with 'show bgp ipv4 unicast' to see what policy filtered

show bgp ipv4 unicast neighbors X.X.X.X received routes

Routes received from neighbor after inbound route-policy (accepted routes)

ExpectedRequires no additional config — IOS XR stores all received routes by default

show rpl route-policy NAME

Display the content of a specific RPL route-policy

ExpectedShows the policy body — verify logic matches intent

show rpl route-policy NAME attachpoints

Show where a route-policy is applied (which neighbors/address-families)

ExpectedLists BGP neighbors and direction (in/out) where this policy is referenced

show bgp process

BGP process information: version, tables, memory usage, scan intervals

ExpectedProcess state: running, shows table versions and prefix counts

show bgp neighbor-group NAME

Display neighbor-group configuration and all members inheriting from it

ExpectedShows full group config and list of neighbors using this group

Debug commands

trace bgp update neighbor X.X.X.X

Per-update tracing for a specific neighbor — more targeted than debug

WarningPreferred over debug in IOS XR for per-neighbor update troubleshooting

debug bgp X.X.X.X all

Full BGP debug for a specific neighbor

WarningVery verbose. Always specify neighbor IP. Run 'undebug all' after.

clear bgp X.X.X.X soft

Soft reset BGP session for a specific neighbor

WarningSafe in production. Hard reset: 'clear bgp X.X.X.X'

show bgp update-group

Show BGP update groups — IOS XR groups neighbors with identical outbound policy for update optimization

WarningSafe diagnostic tool — useful for understanding update group membership

Common mistakes & fixes

SymptomConfig applied but not taking effect

CauseIOS XR uses a two-stage commit model — configuration is staged but not active until 'commit' is run

FixRun 'commit' in configuration mode. Use 'show configuration' to see staged but uncommitted changes. Use 'commit best-effort' to apply valid parts even if some fail.

SymptomNeighbor configured but routes not received or sent — 'No policy for this direction'

CauseIOS XR requires explicit route-policy in AND out for every neighbor or neighbor-group address-family — there is no implicit 'pass all' as in IOS

FixCreate a permissive policy ('route-policy PASS-ALL\n pass\nend-policy') and apply it: 'route-policy PASS-ALL in' and 'route-policy PASS-ALL out' under address-family

SymptomiBGP policy not modifying LOCAL_PREF or NEXT_HOP

CauseIOS XR does not allow modifying certain iBGP attributes on egress by default (RFC 4271 compliance)

FixAdd 'ibgp policy out enforce-modifications' under 'router bgp' to permit attribute modification on iBGP egress

SymptomNeighbor not coming up after config change

CauseConfiguration was not committed — IOS XR requires 'commit' to activate

FixRun 'commit' or 'end' followed by reviewing 'show bgp summary'

SymptomCommunity not passed to eBGP neighbor

CauseIOS XR uses 'send-community-ebgp' (not 'send-community') and it is disabled by default

FixUnder neighbor-group or neighbor address-family: 'send-community-ebgp standard' and/or 'send-community-ebgp extended'

SymptomBFD not detecting failures

CauseBFD not configured on the physical interface, or BFD process not running

FixConfigure on interface: 'bfd minimum-interval 300' and 'bfd multiplier 3'. Verify with 'show bfd session' and 'show bfd neighbors'.

SymptomRoute-policy changes not reflected in BGP table

CauseRoute-policy is evaluated at the time updates are received/sent — existing routes use the old policy until refreshed

FixRun 'clear bgp X.X.X.X soft' to re-apply policies to existing routes without tearing down the session

Further learning

Recommended books to go deeper on this topic.

BGP Design and Implementation

Randy Zhang & Micah Bartell · Cisco Press · The practical BGP bible — iBGP, eBGP, policies, communities, design patterns

Kindle ↗Hardcover ↗Paperback ↗

Internet Routing Architectures

Sam Halabi · Cisco Press · BGP for ISPs and large enterprise — AS path, route reflectors, confederation

Hardcover ↗