Section 1.0: Layer 3 Technologies

Administrative distance, route maps, loop prevention, EIGRP (named-mode, stub, summarization, authentication), OSPFv2 & OSPFv3 (LSA types, area types, virtual links, authentication), eBGP/iBGP (path selection, attributes, route reflectors, communities, peer groups), redistribution between protocols, and Policy-Based Routing.

1.1  Administrative distance (AD)

When two routing sources advertise the same destination prefix with the same prefix length, IOS picks the one with the lowest AD. AD is purely local to the router — it never traverses the wire. Mastering AD is essential for redistribution scenarios because feedback loops are usually solved by manipulating AD.

Default AD values to memorize

Source AD Notes
Connected interface 0 Always wins
Static route 1 Floating static = static with higher AD
eBGP 20 From a different AS
EIGRP (internal) 90 Native EIGRP routes
IGRP 100 Legacy
OSPF 110 All OSPF route types share the same AD
IS-IS 115
RIP 120
EIGRP (external) 170 Routes redistributed into EIGRP
iBGP 200 From the same AS
Unreachable 255 Route is dropped

Visualizing AD selection

Sources advertising 10.0.0.0/24

EIGRP AD 90

OSPF AD 110

RIP AD 120

Route Selection Pick lowest AD EIGRP wins (90)

RIB D 10.0.0.0/24 [90/…]

Floating static: ip route 10.0.0.0 255.0.0.0 192.168.1.1 200 creates a static route with AD 200, used only if all dynamic protocols (OSPF/EIGRP) lose the prefix. Classic backup/failover trick.

1.2  Route maps — the universal policy tool

A route-map is an ordered, sequence-numbered policy with match conditions and set actions. ENARSI uses route-maps everywhere — PBR, redistribution, BGP attributes, EIGRP/OSPF filtering. Master one tool, control all protocols.

Route-map structure

R1(config)# route-map MY_POLICY permit 10
R1(config-route-map)# match ip address prefix-list LANS
R1(config-route-map)# match interface GigabitEthernet0/1
R1(config-route-map)# set metric 5000
R1(config-route-map)# set tag 100
R1(config-route-map)# exit
R1(config)# route-map MY_POLICY permit 20 ! catch-all (no match = match everything)

Reading rules

  • Sequence numbers are evaluated top-down, first match wins.
  • permit + match → apply set and exit.
  • deny + match → reject (filter, do not redistribute).
  • No match statement = match everything.
  • Multiple match statements of the same type = logical OR.
  • Multiple match statements of different types = logical AND.
  • Implicit deny at the end — anything not matched is filtered.

Where route-maps attach

Use case Command
Policy-Based Routing ip policy route-map NAME on an interface
Redistribution filter redistribute ospf 1 route-map FILTER
BGP neighbor inbound/outbound neighbor x.x.x.x route-map IN in
BGP network statement network 10.0.0.0 mask 255.0.0.0 route-map ORIG
EIGRP/OSPF distribute-list distribute-list route-map FILTER in
Common match objects: match ip address (ACL or prefix-list), match ip route-source, match interface, match metric, match tag, match route-type, match community (BGP), match as-path (BGP).
Common set objects: set ip next-hop, set metric, set metric-type, set tag, set local-preference, set as-path prepend, set community, set weight.

1.3  Loop prevention mechanisms

Each protocol has its own loop-avoidance philosophy. ENARSI tests them across all four IGPs/EGP.

Protocol Loop prevention mechanism
RIP Split horizon, route poisoning (16=infinity), hold-down timers, poison reverse, max hop count 15
EIGRP DUAL feasibility condition (FC: ADnbr < FDlocal), split horizon, no inherent area concept
OSPF Link-state SPF computes loop-free SPT per area; inter-area must transit Area 0; LSA flooding boundaries
BGP eBGP: AS_PATH check (drop if own ASN appears). iBGP: split horizon (don’t re-advertise iBGP-learned routes to other iBGP peers → full mesh or RR)
Redistribution Route tagging + match tag + deny in route-map; manipulating AD; filtering with distribute/prefix-list

Tag-based loop prevention (redistribution)

! On router doing OSPF -> EIGRP, tag everything with 100
R1(config)# route-map OSPF_TO_EIGRP permit 10
R1(config-route-map)# set tag 100
R1(config)# router eigrp 100
R1(config-router)# redistribute ospf 1 metric 10000 100 255 1 1500 route-map OSPF_TO_EIGRP

! On router doing EIGRP -> OSPF, drop anything tagged 100 (loop)
R2(config)# route-map EIGRP_TO_OSPF deny 10
R2(config-route-map)# match tag 100
R2(config-route-map)# route-map EIGRP_TO_OSPF permit 20
R2(config)# router ospf 1
R2(config-router)# redistribute eigrp 100 subnets route-map EIGRP_TO_OSPF

1.4  EIGRP — advanced features

DUAL recap — Successor & Feasible Successor

  • FD (Feasible Distance) — lowest metric to a destination from the local router.
  • RD/AD (Reported / Advertised Distance) — metric the neighbor reports to the destination.
  • Successor — primary route (lowest FD), installed in RIB.
  • Feasible Successor (FS) — backup that satisfies the Feasibility Condition: RDnbr < FDlocal. Loop-free; instant failover.
FD=20 via R2 (Successor) FD=30 via R3 (Feasible Successor, RD=15 < FD=20)

R1 R2 R3 10.1.1.0 /24

EIGRP stub routing

A stub router announces itself as a stub; the hub will never send queries to a stub. Massive scaling benefit, prevents SIA (Stuck-In-Active).

SPOKE(config-router-af)# eigrp stub ! defaults to connected + summary
SPOKE(config-router-af)# eigrp stub connected summary static redistributed receive-only leak-map LM

Stub options: connected, summary, static, redistributed, receive-only, leak-map (selectively leak prefixes that would otherwise be filtered).

EIGRP authentication — classic vs named-mode

! Classic mode — per-interface MD5 keychain
R1(config)# key chain EIGRP_KC
R1(config-keychain)# key 1
R1(config-keychain-key)# key-string Cisco123!
R1(config)# interface Gi0/1
R1(config-if)# ip authentication mode eigrp 100 md5
R1(config-if)# ip authentication key-chain eigrp 100 EIGRP_KC

! Named-mode — HMAC-SHA-256 (modern, ENARSI v1.1)
R1(config)# router eigrp NAMED
R1(config-router)# address-family ipv4 unicast autonomous-system 100
R1(config-router-af)# af-interface Gi0/1
R1(config-router-af-int)# authentication mode hmac-sha-256 Cisco123!

EIGRP summarization, passive-interface, filtering

! Manual summary on egress interface
R1(config-if)# ip summary-address eigrp 100 10.0.0.0 255.0.0.0

! Passive-interface (no hellos, no neighbors on this iface)
R1(config-router)# passive-interface default
R1(config-router)# no passive-interface Gi0/1

! Filter outbound on Gi0/1 with prefix-list
R1(config)# ip prefix-list NO_DEFAULT seq 5 deny 0.0.0.0/0
R1(config)# ip prefix-list NO_DEFAULT seq 10 permit 0.0.0.0/0 le 32
R1(config)# router eigrp 100
R1(config-router)# distribute-list prefix NO_DEFAULT out Gi0/1

Gotcha: passive-interface on EIGRP/OSPF stops Hello packets — no neighbor will form. On RIP it just stops updates, but the interface still receives them. Different behavior per protocol.

1.5  OSPFv2 & OSPFv3 — LSAs, areas, virtual links

The 7 OSPF LSA types you must know cold

Type Name Originator Scope
1 Router LSA Every router Within its area only
2 Network LSA DR on multi-access segments Within the area
3 Summary (Inter-Area Prefix) LSA ABR Across area boundaries
4 ASBR-Summary LSA ABR Tells other areas how to reach the ASBR
5 External LSA ASBR Flooded throughout the OSPF domain (except stub/NSSA)
7 NSSA External LSA ASBR inside an NSSA Within the NSSA; ABR translates to Type 5 leaving the NSSA
9-11 Opaque LSAs Various (TE, Segment Routing) Link / area / AS scope

OSPF area types — what’s allowed

Area type Type 1/2 Type 3 (inter-area) Type 4/5 (external) Type 7 (NSSA) ABR injects default?
Standard / Backbone ✓ ✓ ✓ — No
Stub ✓ ✓ ✗ ✗ Yes (Type 3)
Totally Stubby ✓ ✗ ✗ ✗ Yes (Type 3)
NSSA ✓ ✓ ✗ ✓ Optional
Totally NSSA ✓ ✗ ✗ ✓ Yes (Type 3)
! Stub: configured on EVERY router in the area
Rx(config-router)# area 1 stub

! Totally Stubby: stub no-summary on the ABR only; stub on others
ABR(config-router)# area 1 stub no-summary

! NSSA: every router in area
Rx(config-router)# area 2 nssa

! Totally NSSA: nssa no-summary on ABR; nssa on others
ABR(config-router)# area 2 nssa no-summary

Virtual links — rescuing a discontiguous backbone

All non-backbone areas must touch Area 0. If a remote area is separated from Area 0, a virtual link tunnels the adjacency through a transit area (must be a standard area — never stub).

! Transit area is Area 1; remote ABR has RID 3.3.3.3, backbone ABR has RID 2.2.2.2
ABR1(config-router)# area 1 virtual-link 3.3.3.3
ABR3(config-router)# area 1 virtual-link 2.2.2.2
ABR1# show ip ospf virtual-links

OSPFv2 vs OSPFv3 differences

Aspect OSPFv2 OSPFv3
Address family IPv4 only IPv6 native; IPv4 via Address Family extension (RFC 5838)
Adjacency Subnet-based Per-link (link-local addresses)
Router ID 32-bit, often highest loopback 32-bit, must be configured if no IPv4 address
Authentication Plain/MD5 in OSPF header Originally IPsec AH/ESP; now built-in keychains supported
New LSAs — Type 8 (Link-LSA), Type 9 (Intra-Area Prefix LSA)
Multicast 224.0.0.5 / 224.0.0.6 FF02::5 / FF02::6

OSPF authentication (named keychain — modern)

R1(config)# key chain OSPF_KC
R1(config-keychain)# key 1
R1(config-keychain-key)# key-string Cisco123!
R1(config-keychain-key)# cryptographic-algorithm hmac-sha-256
R1(config)# interface Gi0/1
R1(config-if)# ip ospf authentication key-chain OSPF_KC

1.6  BGP — eBGP, iBGP, path selection, RR, communities

eBGP vs iBGP — the core distinction

Aspect eBGP iBGP
Peers in Different AS numbers Same AS number
TTL by default 1 (directly connected) 255 (multi-hop OK)
AD 20 200
Next-hop on advertise Changes to self Preserved (use next-hop-self)
AS_PATH on advertise Prepends own ASN Unchanged
Loop prevention AS_PATH check Split horizon (no re-advertise iBGP→iBGP)
Topology required Direct Full mesh, OR Route Reflector, OR Confederation

BGP path-selection algorithm — in order

For prefixes with multiple paths, BGP walks down this list, stopping at the first tie-breaker that picks a winner.

  1. Weight — highest (Cisco-only, local to router)
  2. LOCAL_PREF — highest (within an AS, default 100)
  3. Locally originated — network/aggregate-address/redistribute beats learned
  4. AS_PATH — shortest length
  5. Origin — IGP (i) > EGP (e) > Incomplete (?)
  6. MED — lowest (only compared within same neighboring AS)
  7. eBGP over iBGP — prefer external
  8. Lowest IGP metric to next-hop
  9. Older eBGP path (stability)
  10. Lowest router ID
  11. Shortest cluster list length (RR scenario)
  12. Lowest neighbor IP
Mnemonic: “We Love Oranges And Oranges Mean Pure Refreshment” — Weight, Local-pref, Originated, AS-path, Origin, MED, Path (eBGP/iBGP), Router ID.

Attribute classification

Class Attributes Behavior
Well-known mandatory AS_PATH, NEXT_HOP, ORIGIN Must be in every UPDATE; recognized by all
Well-known discretionary LOCAL_PREF, ATOMIC_AGGREGATE Recognized by all; optional to send
Optional transitive AGGREGATOR, COMMUNITY Forwarded even if not understood
Optional non-transitive MED, ORIGINATOR_ID, CLUSTER_LIST Dropped if not understood

iBGP scaling — Route Reflector (RR)

iBGP requires a full mesh (n(n-1)/2 sessions). Two solutions:

  • Route Reflector — one router (RR) reflects routes between iBGP clients. Loop prevention via ORIGINATOR_ID and CLUSTER_LIST.
  • Confederation — carve a single AS into sub-ASes, treat them like eBGP between them.

RR AS 65000

Client A RR-client

Client B RR-client

Client C RR-client

Each client peers ONLY with the RR. RR re-advertises iBGP routes to other clients.

RR(config)# router bgp 65000
RR(config-router)# neighbor 10.1.1.1 remote-as 65000
RR(config-router)# neighbor 10.1.1.1 route-reflector-client
RR(config-router)# neighbor 10.1.1.2 remote-as 65000
RR(config-router)# neighbor 10.1.1.2 route-reflector-client

BGP communities — tags carried with routes

Communities are 32-bit values written as ASN:value. Commonly used to flag routes for downstream policy.

  • NO_EXPORT — do not advertise outside local AS
  • NO_ADVERTISE — do not advertise to any peer
  • LOCAL_AS — do not advertise outside local sub-AS (in confederations)
  • INTERNET — advertise everywhere (default)
R1(config)# route-map TAG_INFRA permit 10
R1(config-route-map)# match ip address prefix-list INFRA
R1(config-route-map)# set community 65000:100 no-export additive
R1(config)# router bgp 65000
R1(config-router)# neighbor 192.0.2.1 send-community
R1(config-router)# network 10.0.0.0 mask 255.0.0.0 route-map TAG_INFRA

Peer groups & peer templates

Apply a single configuration to many neighbors and reduce CPU cost (single UPDATE generated, replicated).

R1(config-router)# neighbor SPOKES peer-group
R1(config-router)# neighbor SPOKES remote-as 65000
R1(config-router)# neighbor SPOKES update-source Loopback0
R1(config-router)# neighbor SPOKES route-reflector-client
R1(config-router)# neighbor 10.1.1.1 peer-group SPOKES
R1(config-router)# neighbor 10.1.1.2 peer-group SPOKES

1.7  Route redistribution & filtering

Redistribution moves routes between protocols. Three problems must be managed: seed metrics, routing loops, and suboptimal routing.

Seed metrics — what to set when

Into ↓ Seed metric required? How to specify
OSPF Default = 20 (BGP=1). Use subnets keyword! redistribute eigrp 100 metric 100 subnets
EIGRP Yes, required: BW, Delay, Reliability, Load, MTU redistribute ospf 1 metric 10000 100 255 1 1500
RIP Yes, hop count redistribute ospf 1 metric 5
BGP Optional (uses IGP metric as MED) redistribute ospf 1
OSPF gotcha: without the subnets keyword, only classful networks are redistributed. Subnets like 10.1.1.0/24 are silently dropped. Always use subnets.

External route metric types

  • OSPF E1 — cost = redistributed metric + cumulative path cost (changes per hop). Best when you want path selection to consider transit cost.
  • OSPF E2 (default) — cost = redistributed metric only (does not change). Use when external metric should dominate.
  • EIGRP external — AD 170 instead of 90.
  • BGP origin code — i for network, ? for redistribute.

Filtering tools at redistribution

Tool Granularity Typical use
distribute-list ACL Per prefix (no length match) Quick filtering with std/ext ACL
distribute-list prefix Per prefix & length Precise prefix-length filtering
route-map (with deny seq) Match anything, set anything Tag-and-filter loop prevention
Tag (set tag / match tag) Stamp routes for downstream filtering Two-way redistribution loops
Modify AD per protocol Whole protocol Force one source to lose to another

Mutual redistribution — the loop trap

OSPF Domain 10.10.0.0/16

EIGRP Domain 10.20.0.0/16

R1 R2

Two redistribution points = loop risk — tag & filter!

1.8  Policy-Based Routing (PBR)

PBR overrides destination-based routing using a route-map applied to an interface. Match on source IP, application, packet length, ToS — then set next-hop, output interface, IP precedence, etc.

Configuration steps

  1. Define an ACL (or prefix-list) matching interesting traffic.
  2. Create a route-map with match ip address & set ip next-hop.
  3. Apply with ip policy route-map NAME on the ingress interface.
  4. For traffic generated by the router itself: ip local policy route-map NAME in global config.
R1(config)# ip access-list extended VOICE
R1(config-ext-nacl)# permit udp any any range 16384 32767

R1(config)# route-map PBR_VOICE permit 10
R1(config-route-map)# match ip address VOICE
R1(config-route-map)# set ip next-hop verify-availability 10.0.0.1 10 track 1
R1(config-route-map)# set ip precedence 5
R1(config)# route-map PBR_VOICE permit 20 ! catch-all = normal routing

R1(config)# interface Gi0/0
R1(config-if)# ip policy route-map PBR_VOICE

Verification: show ip policy shows interfaces. show route-map shows match counters. debug ip policy shows live decisions (use carefully on production).

PBR with object tracking (resilient PBR)

Combine PBR with track objects so the policy backs out automatically when the next-hop or SLA fails.

R1(config)# ip sla 1
R1(config-ip-sla)# icmp-echo 10.0.0.1
R1(config-ip-sla)# frequency 5
R1(config)# ip sla schedule 1 life forever start-time now
R1(config)# track 1 ip sla 1 reachability
R1(config)# route-map PBR_VOICE permit 10
R1(config-route-map)# set ip next-hop verify-availability 10.0.0.1 10 track 1

Hands-on labs (8)

Lab 1 — EIGRP named-mode with HMAC-SHA-256 + summarization + stub
! HUB router (R1)
R1(config)# router eigrp HQ
R1(config-router)# address-family ipv4 unicast autonomous-system 100
R1(config-router-af)# network 10.0.0.0 0.255.255.255
R1(config-router-af)# af-interface Gi0/1
R1(config-router-af-int)# authentication mode hmac-sha-256 EnArSi2026
R1(config-router-af-int)# summary-address 10.10.0.0 255.255.0.0
R1(config-router-af-int)# exit-af-interface

! SPOKE (R2) — stub
R2(config)# router eigrp BRANCH
R2(config-router)# address-family ipv4 unicast autonomous-system 100
R2(config-router-af)# network 10.20.0.0 0.0.255.255
R2(config-router-af)# eigrp stub connected summary
R2(config-router-af)# af-interface Gi0/1
R2(config-router-af-int)# authentication mode hmac-sha-256 EnArSi2026

! Verify
R1# show eigrp address-family ipv4 neighbors detail
R1# show eigrp address-family ipv4 topology
R1# show ip protocols

Lab 2 — OSPF multi-area with NSSA + virtual link
! Topology: Area 2 — Area 1 — Area 0 (Area 1 is a non-stub transit)
! ^ NSSA

! ABR1 (Area 0 <-> Area 1) RID 1.1.1.1
ABR1(config)# router ospf 1
ABR1(config-router)# router-id 1.1.1.1
ABR1(config-router)# network 10.0.0.0 0.0.0.3 area 0
ABR1(config-router)# network 10.0.1.0 0.0.0.3 area 1
ABR1(config-router)# area 1 virtual-link 3.3.3.3

! ABR2 (Area 1 <-> Area 2 NSSA) RID 3.3.3.3
ABR2(config)# router ospf 1
ABR2(config-router)# router-id 3.3.3.3
ABR2(config-router)# network 10.0.1.0 0.0.0.3 area 1
ABR2(config-router)# network 10.0.2.0 0.0.0.3 area 2
ABR2(config-router)# area 2 nssa default-information-originate
ABR2(config-router)# area 1 virtual-link 1.1.1.1

! Internal router in NSSA Area 2
R5(config-router)# area 2 nssa

! Verify
ABR1# show ip ospf virtual-links
ABR2# show ip ospf database nssa-external
R5# show ip route ospf

Lab 3 — OSPFv3 for IPv6 with named keychain authentication
R1(config)# ipv6 unicast-routing
R1(config)# key chain OSPFv3_KC
R1(config-keychain)# key 1
R1(config-keychain-key)# key-string Cisco123!
R1(config-keychain-key)# cryptographic-algorithm hmac-sha-256

R1(config)# router ospfv3 1
R1(config-router)# router-id 1.1.1.1
R1(config-router)# address-family ipv6 unicast
R1(config-router-af)# exit-address-family

R1(config)# interface Gi0/1
R1(config-if)# ipv6 address 2001:db8::1/64
R1(config-if)# ospfv3 1 ipv6 area 0
R1(config-if)# ospfv3 authentication key-chain OSPFv3_KC

R1# show ospfv3 neighbor
R1# show ipv6 route ospf

Lab 4 — eBGP between AS 65001 and AS 65002 with route filtering
! R1 in AS 65001 <—-eBGP—-> R2 in AS 65002

R1(config)# ip prefix-list TO_R2 seq 10 permit 10.1.0.0/16
R1(config)# ip prefix-list TO_R2 seq 20 permit 10.2.0.0/16
R1(config)# route-map OUT_TO_R2 permit 10
R1(config-route-map)# match ip address prefix-list TO_R2
R1(config-route-map)# set as-path prepend 65001 65001

R1(config)# router bgp 65001
R1(config-router)# bgp router-id 1.1.1.1
R1(config-router)# neighbor 192.0.2.2 remote-as 65002
R1(config-router)# neighbor 192.0.2.2 password Cisco123!
R1(config-router)# neighbor 192.0.2.2 route-map OUT_TO_R2 out
R1(config-router)# network 10.1.0.0 mask 255.255.0.0
R1(config-router)# network 10.2.0.0 mask 255.255.0.0

R1# show bgp ipv4 unicast summary
R1# show bgp ipv4 unicast neighbors 192.0.2.2 advertised-routes

Lab 5 — iBGP with Route Reflector + community-based policy
! RR (10.0.0.1) reflects between Client A (10.0.0.2) and Client B (10.0.0.3)

RR(config)# ip community-list standard NO_EXP permit no-export
RR(config)# route-map FROM_CLIENT permit 10
RR(config-route-map)# match community NO_EXP
RR(config-route-map)# set local-preference 200

RR(config)# router bgp 65000
RR(config-router)# neighbor RR_CLIENTS peer-group
RR(config-router)# neighbor RR_CLIENTS remote-as 65000
RR(config-router)# neighbor RR_CLIENTS update-source Loopback0
RR(config-router)# neighbor RR_CLIENTS route-reflector-client
RR(config-router)# neighbor RR_CLIENTS send-community
RR(config-router)# neighbor RR_CLIENTS route-map FROM_CLIENT in
RR(config-router)# neighbor 10.0.0.2 peer-group RR_CLIENTS
RR(config-router)# neighbor 10.0.0.3 peer-group RR_CLIENTS

RR# show bgp ipv4 unicast 10.5.0.0
RR# show ip bgp neighbors 10.0.0.2 advertised-routes

Lab 6 — Two-way redistribution OSPF ↔ EIGRP with tag-based loop prevention
! Both edge routers (R1 and R2) are running OSPF AND EIGRP simultaneously

! Outbound (OSPF -> EIGRP): tag with 1000
R1(config)# route-map OSPF_TO_EIGRP deny 10
R1(config-route-map)# match tag 2000 ! drop routes that came from EIGRP-side
R1(config)# route-map OSPF_TO_EIGRP permit 20
R1(config-route-map)# set tag 1000

! Outbound (EIGRP -> OSPF): tag with 2000
R1(config)# route-map EIGRP_TO_OSPF deny 10
R1(config-route-map)# match tag 1000 ! drop routes that came from OSPF-side
R1(config)# route-map EIGRP_TO_OSPF permit 20
R1(config-route-map)# set tag 2000

R1(config)# router ospf 1
R1(config-router)# redistribute eigrp 100 subnets route-map EIGRP_TO_OSPF
R1(config)# router eigrp 100
R1(config-router)# redistribute ospf 1 metric 10000 100 255 1 1500 route-map OSPF_TO_EIGRP

! Repeat the EXACT same config on R2 — tags carry across redistribution and stop the loop

Lab 7 — Policy-Based Routing for source-based path selection
! Goal: 10.10.10.0/24 (HR) goes via ISP-A; everything else via default

R1(config)# ip access-list extended HR_TRAFFIC
R1(config-ext-nacl)# permit ip 10.10.10.0 0.0.0.255 any

R1(config)# ip sla 10
R1(config-ip-sla)# icmp-echo 198.51.100.1 source-interface Gi0/1
R1(config-ip-sla)# frequency 5
R1(config)# ip sla schedule 10 life forever start-time now
R1(config)# track 10 ip sla 10 reachability

R1(config)# route-map PBR_HR permit 10
R1(config-route-map)# match ip address HR_TRAFFIC
R1(config-route-map)# set ip next-hop verify-availability 198.51.100.1 1 track 10

R1(config)# interface Gi0/0
R1(config-if)# ip policy route-map PBR_HR

R1# show ip policy
R1# show route-map PBR_HR
R1# show track 10

Lab 8 — BGP attribute manipulation (Local Preference + AS-Path prepend)
! Goal: Prefer ISP1 (next-hop 192.0.2.1) for outbound; advertise less attractively to ISP2 inbound

R1(config)# route-map FROM_ISP1 permit 10
R1(config-route-map)# set local-preference 200 ! higher = preferred

R1(config)# route-map FROM_ISP2 permit 10
R1(config-route-map)# set local-preference 100 ! default

R1(config)# route-map TO_ISP2 permit 10
R1(config-route-map)# set as-path prepend 65001 65001 65001 ! make our routes look longer

R1(config)# router bgp 65001
R1(config-router)# neighbor 192.0.2.1 remote-as 64500
R1(config-router)# neighbor 192.0.2.1 route-map FROM_ISP1 in
R1(config-router)# neighbor 198.51.100.1 remote-as 64501
R1(config-router)# neighbor 198.51.100.1 route-map FROM_ISP2 in
R1(config-router)# neighbor 198.51.100.1 route-map TO_ISP2 out

R1# show bgp ipv4 unicast
R1# show bgp ipv4 unicast 0.0.0.0/0

Check Your Understanding

Twenty-five questions on this section. Each answer is explained as you go.

1. 

Two routes for 10.0.0.0/24 arrive at R1: one via OSPF (cost 50), one via internal EIGRP. Which one wins?

2. 

The default AD of an external EIGRP route is…

3. 

In a route-map, which combination is true?

4. 

EIGRP feasibility condition (FC) for a Feasible Successor is…

5. 

In an EIGRP-named-mode router, where is HMAC-SHA-256 authentication applied?

6. 

Which OSPF area type permits Type 7 LSAs but blocks Type 5?

7. 

Which router originates an OSPF Type 4 LSA?

8. 

A virtual link can transit which kind of area?

9. 

OSPFv3 uses which multicast addresses?

10. 

In BGP path selection, what is the FIRST tie-breaker considered?

11. 

Local Preference is exchanged with which peer types?

12. 

The MED attribute is…

13. 

To prevent iBGP-learned routes from being re-advertised to other iBGP peers, BGP uses…

14. 

Which two BGP attributes prevent loops in a Route Reflector cluster?

15. 

The well-known community NO_EXPORT means…

16. 

When redistributing into OSPF, which keyword is required to redistribute non-classful (subnetted) prefixes?

17. 

The default external metric type for redistributed OSPF routes is…

18. 

To redistribute into EIGRP, you must specify five seed metric values. Which five?

19. 

The simplest mutual-redistribution loop-prevention technique is…

20. 

PBR is applied to the…

21. 

To make PBR fall back to normal routing when the policy next-hop is unreachable, use…

22. 

What does passive-interface default do under router eigrp 100?

23. 

An EIGRP stub router…

24. 

A floating static route is created by…

25. 

Which BGP attribute classification applies to MED?

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