Exam weight: 30% | Labs: 6 | ← Back to CCNP ENCOR
3.1 Layer 2 Infrastructure
VLANs and 802.1Q Trunking
802.1Q inserts a 4-byte tag between source MAC and EtherType fields to carry multiple VLANs across a single link.
- Native VLAN transmits untagged frames (default VLAN 1 — change recommended)
- DTP auto-negotiates trunks; disable on edge ports
- VTP v3 supports extended VLANs (1006–4094) and MST configuration
EtherChannel
| Protocol | Standard | Modes | Key Detail |
|---|---|---|---|
| LACP | IEEE 802.3ad | active/passive | Active+active or active+passive forms channel |
| PAgP | Cisco proprietary | desirable/auto | Desirable+desirable or desirable+auto |
| Static | — | on | Both sides must be “on”; no negotiation |
Prerequisites: All member ports must match speed, duplex, access/trunk mode, native VLAN, allowed VLANs, and STP settings.
Spanning Tree: RSTP and MST
RSTP (802.1w) converges in 1–2 seconds vs. 30–50 seconds for legacy 802.1D.
- Root Port: Best path to Root Bridge (one per non-root switch)
- Designated Port: Best port on segment toward Root Bridge
- Alternate Port: Backup to Root Bridge (replaces Blocking)
- Backup Port: Redundant path on same segment
- Edge Port: PortFast-enabled; forwards immediately
MST (802.1s) maps multiple VLANs to single STP instance. Requires matching: region name, revision number, VLAN-to-instance mappings.
3.2 Layer 3 Routing
EIGRP
- IP protocol 88; Multicast 224.0.0.10
- AD: 90 (internal) / 170 (external)
- Metric: Composite (bandwidth + delay + optional load/reliability)
- Hello/Hold: 5s/15s (LAN) or 60s/180s (WAN)
- DUAL: Routes are Passive (converged) or Active (querying). Stuck-in-Active after 3 minutes triggers neighbor reset.
OSPF Multi-Area
All areas connect to Area 0; inter-area routing flows through ABRs.
| LSA Type | Name | Scope |
|---|---|---|
| Type 1 | Router LSA | Within area |
| Type 2 | Network LSA | Within area (DR generated) |
| Type 3 | Summary LSA | Inter-area |
| Type 4 | ASBR Summary | Points to ASBR |
| Type 5 | External LSA | Entire domain |
| Type 7 | NSSA External | Within NSSA |
| Area Type | Blocks | Allows |
|---|---|---|
| Regular | Nothing | All |
| Stub | Type 4, 5 | Default from ABR |
| Totally Stub | Type 3, 4, 5 | Default from ABR |
| NSSA | Type 5 | Type 7 |
| Totally NSSA | Type 3, 4, 5 | Type 7 |
eBGP
Best-Path Selection Order: Weight → Local Preference → Locally Originated → AS-Path Length → Origin → MED → eBGP over iBGP → IGP Metric → Router-ID
- Default TTL=1 requires direct peering; use
ebgp-multihop <ttl>for loopback-based peering - Weight: Cisco local, highest preferred
- Local Preference: within AS, highest preferred
- MED: lowest preferred, hints to neighbor AS
Route Redistribution
- Seed metric required when redistributing into EIGRP
- OSPF external routes default to E2 (fixed metric); E1 adds internal cost
- Use route-maps with tags to prevent loops in two-way redistribution
3.3 Wireless Infrastructure
RF Fundamentals
- RSSI: ≥-67 dBm for enterprise; -50 excellent, -70 marginal, -80+ poor
- SNR: ≥25 dB required; higher is better
- 2.4 GHz: 3 non-overlapping channels (1, 6, 11); prone to interference
- 5 GHz: 25 non-overlapping 20 MHz channels; supports channel bonding (40/80/160 MHz)
AP Modes
- Local: Default; serves clients via CAPWAP tunnel to WLC
- FlexConnect: Local switching when WLC unreachable
- Monitor: Passive scanning for rogue APs and interference
- Sniffer: Captures 802.11 frames for Wireshark
- SE-Connect: CleanAir spectrum analysis
- Bridge/Mesh: Outdoor wireless backhaul
CAPWAP Join Sequence
Discovery (DHCP opt 43/DNS/broadcast/prior WLC) → Discovery Response → DTLS Handshake → Join Request/Response → Configuration and Image Download
Wireless Tags (IOS-XE WLC)
- Policy Tag: Maps SSID to Policy Profile (VLAN, QoS, ACL)
- Site Tag: Assigns AP join and flex profiles
- RF Tag: Sets RF Profile (RSSI thresholds, channel, power)
3.4 IP Services
NTP
- Stratum 0: Reference clock (atomic, GPS)
- Stratum 16: Unsynchronized
- MD5 authentication supported;
ntp mastermakes router authoritative
NAT / PAT Types
- Static NAT: One-to-one fixed mapping (servers)
- Dynamic NAT: Many-to-many pool allocation
- PAT (NAT Overload): Many-to-one via port numbers (most common)
Multicast
- IGMP v2: Adds Leave Group; ~3-second pruning (enterprise standard)
- PIM Dense Mode: Flood-and-prune; dense populations
- PIM Sparse Mode: RP-based; enterprise standard
- SSM: Source-specific; no RP needed; 232.0.0.0/8
- RPF Check: Packet accepted only if arriving on interface used to reach source/RP
Hands-On Labs
Lab 1: 802.1Q Trunking and LACP EtherChannel
Create trunk carrying VLANs 10, 20, 30 with native VLAN 99. Bundle Gi0/2–0/3 into LACP port-channel 1 (active/passive). Verify: show etherchannel summary, show interfaces trunk.
Lab 2: RSTP and MST Configuration
Enable Rapid PVST+; set SW1 as root for VLANs 10,20 and SW2 for VLANs 30,99. Configure MST with two instances: MSTI 1 (VLANs 10,20) and MSTI 2 (VLANs 30,99).
Lab 3: OSPF Multi-Area with Summarization
Three-router topology: R1 in Area 1, R2 as ABR, R3 in Area 0. Configure area ranges on ABR to summarize Area 1 networks.
Lab 4: eBGP Peering and Verification
Configure eBGP between R1 (AS 65001) and R2 (AS 65002). Verify: show bgp summary, show bgp ipv4 unicast.
Lab 5: NAT Overload (PAT) + NTP
Configure PAT for 192.168.1.0/24 via interface overload. Set up NTP hierarchy with MD5 authentication.
Lab 6: PIM-SM Multicast Configuration
Enable IP multicast routing; configure PIM Sparse Mode. Designate R2 as static RP for 239.0.0.0/8. Verify: show ip pim rp mapping, show ip mroute.
