Section 31: WAN - Wide Area Networks

What are the four Internet redundancy topology options with a single ISP vs. multiple ISPs?

Single Homed (one router, one ISP), Dual Homed (two routers, one ISP), Multihomed (one router, two ISPs), Dual Multihomed (two routers, cross-connected to two ISPs).

In WAN topology terms, what defines a Full Mesh topology?

Every site has a direct connection to every other site

What's the benefit of using GRE over IPsec together, rather than either alone?

You get IPsec's encryption plus GRE's multicast support — IPsec alone doesn't support multicast, but GRE does

What does DWDM stand for, and what does it do?

Dense Wavelength Division Multiplexing — combines/multiplexes multiple optical signals onto a single fiber strand

Do Customer Edge (CE) routers run MPLS?

No — CE routers peer at Layer 3 with the provider's PE routers, but MPLS runs across the provider's core on the PE and P routers only.

What does PPPoE stand for?

Point-to-Point Protocol over Ethernet

What bandwidth does a T1 leased line offer?

1.544 Mbps

What is DMVPN, and what's its key advantage over a standard hub-and-spoke VPN?

Dynamic Multipoint VPN — Cisco proprietary, provides scalable hub-and-spoke configuration while also enabling direct full-mesh (spoke-to-spoke) connectivity between sites

What is GETVPN, and what are its defining characteristics?

Group Encrypted Transport VPN — Cisco proprietary, uses a central key server for centralized policy/key management, designed to secure traffic over a private WAN (like MPLS) without adding tunnels. Uses IPsec transport mode, which preserves the original IP header.

What Site-to-Site VPN option is open standard, and what's its key limitation?

IPsec Tunnel — open standard, but does not support multicast.

What does VPLS stand for, and what type of connectivity does it provide?

Virtual Private LAN Service — a multipoint Layer 2 MPLS VPN

What does VPWS stand for, and what type of connectivity does it provide?

Virtual Private Wire Service (uses pseudowires) — a point-to-point Layer 2 VPN.

What does DSL stand for?

Digital Subscriber Line.

What does MPLS stand for?

Multi Protocol Label Switching.

What's the key difference between Remote Access VPN and Site-to-Site VPN in terms of endpoints?

Remote Access VPN connects an individual user's device (with VPN software) to an office router/firewall. Site-to-Site VPN connects router/firewall to router/firewall between offices — no software needed on user desktops.

How do LAN, MAN, and WAN differ in scope?

LAN = single building or building group. MAN = larger than a LAN but smaller than a WAN (e.g. connecting multiple campuses within the same city). WAN = geographically distributed, connecting multiple LANs together.

What is IPsec VTI, and how does it differ from a standard open-standard IPsec tunnel?

IPsec VTI (Virtual Tunnel Interface) is a Cisco-proprietary, simplified configuration between two Cisco devices — unlike standard IPsec tunnels, it supports multicast.

What is "dark fiber," and why does it exist?

Unused optical fiber cabling — service providers often laid more fiber than needed, since DWDM later let them multiplex much more capacity onto existing strands, leaving surplus cable unlit.

What are the "primary" WAN connectivity options (with an SLA), vs. the smaller-office/backup options (without one)?

Primary (with SLA guarantees): Leased Lines, MPLS, Satellite. Smaller office/backup (no corporate SLA, going over the Internet): DSL, Cable, Wireless (e.g. 4G).

What are considered legacy WAN technologies for the CCNA exam?

Frame Relay, ATM, X.25, ISDN, and PSTN dial-up.

What bandwidth do T1 and E1 leased lines offer, and where is each used?

T1 = 1.544 Mbps (North America). E1 = 2 Mbps (Europe and most of the rest of the world).

For the CCNA exam, what physical interface type do Leased Lines use?

Serial — not Ethernet.

What's the key difference between a Layer 3 and Layer 2 MPLS VPN regarding CE routers and IP subnets?

Layer 3: CE routers peer at Layer 3 with the PE (different sites are in different IP subnets). Layer 2: CE devices don't peer with the PE at all — the provider network is transparent, acting like a giant switch, and all sites can be in the same IP sub

Can different MPLS VPN customers use the same IP subnet on the shared provider infrastructure?

Yes — customers are kept strictly separate with separate routing tables, so overlapping subnets between different customers cause no conflict.

What's the practical difference between VPLS and VPWS in terms of number of sites?

VPLS (multipoint) connects more than 2 sites in the same Layer 2 domain. VPWS (point-to-point) connects exactly 2 sites.

What's the main advantage and disadvantage of a Redundant Hub-and-Spoke topology compared to standard Hub-and-Spoke?

Advantage: removes the single point of failure (a second hub site provides backup). Disadvantage: higher cost (roughly doubles the number of links) — traffic flow is still suboptimal since branch-to-branch traffic still routes through a hub.

What is a Partial Mesh topology, and why would you use it over Hub-and-Spoke or Full Mesh?

A hub-and-spoke topology with a few additional direct spoke-to-spoke links added — a cost/performance trade-off, giving more direct paths between select high-traffic sites without the full cost of a complete mesh.

Where is PPPoE typically configured in a DSL deployment — the modem or the router?

Usually the DSL modem, though it can be configured on the router instead depending on regional/provider convention.