VPN Types — Site-to-Site, Remote Access, GRE, NAT-T
A VPN is an encrypted tunnel over an insecure network (usually the internet) that connects networks or users securely as if they were directly connected. Facts Point Info OSI layer Layer 3 (IPsec), Layer 2/3 (GRE over IPsec) Standard IPsec = IETF (RFC 4301 etc.) Encryption AES (3DES = legacy, don’t use) Authentication Pre-shared key, […]
WAN Technologies — From Leased Lines to SD-WAN
WAN (Wide Area Network) connects geographically separated networks via service providers using dedicated, packet-switched or internet-based technologies. Key topics (CCNA / CCNP) WAN topologies (point-to-point, hub-and-spoke, mesh) · circuit- vs packet-switched · MPLS & MPLS VPN · internet-based WAN (DSL, cable, fiber, LTE/5G) · VPN (site-to-site, remote access) · SD-WAN architecture & benefits · WAN […]
MPLS — Labels, LDP & Layer 3 VPN
MPLS forwards packets based on labels instead of IP lookups and enables scalable VPN solutions and traffic engineering. Facts Point Fact Technology Multiprotocol Label Switching OSI layer Between L2 and L3 (Layer 2.5) Forwarding Label-based, not IP longest-prefix match Classification Traffic grouped in FEC (Forwarding Equivalence Class) Label size 32-bit header (20-bit label + TC […]
NAT in Four Flavours — Static, Dynamic, PAT
NAT (Network Address Translation) translates IP addresses (and sometimes ports) between private and public networks. Facts Term Explanation Inside local The private IP address (before NAT) Inside global The public IP address (after NAT) Outside global The actual IP of the external destination Outside local How the external IP is seen internally NAT table Mapping […]
QoS — EF, LLQ & the Trust Boundary
QoS ensures that delay-sensitive traffic (voice and video) is prioritized correctly under network load. Facts Term Explanation Latency Delay from sender to receiver Jitter Variation in latency (very critical for voice) Packet loss Lost packets (very critical for voice/video) Bandwidth Available capacity Congestion Traffic exceeds link capacity Classification Identifying traffic Marking Marking traffic (DSCP/CoS) Queuing […]
SLAAC vs DHCPv6
SLAAC: the IPv6 client builds its own address based on Router Advertisements (RA). DHCPv6: a server assigns IPv6 addresses and/or other parameters – stateless (client still uses SLAAC, DHCPv6 only supplies DNS etc.) or stateful (the server assigns the address itself and tracks clients). Comparison Point SLAAC DHCPv6 stateless DHCPv6 stateful Assigns IPv6 address ✅ […]
Prefix-Lists & the Route Filtering Stack
Prefix-lists are a precise and scalable tool to filter routes based on network prefix and prefix length – mainly used in routing (especially BGP). Facts (Key Topic) Point Explanation Purpose Filter routing prefixes (NOT traffic – that’s ACLs) Matches Network + prefix length Typical use BGP, OSPF (via route-maps), EIGRP Key parameters permit/deny, seq, ge, […]
Summarization vs Aggregation (Null0)
Route summarization/aggregation combines several more specific routes into one summary route: 10.1.1.0/24 10.1.2.0/24 → 10.1.0.0/16 Why use it? Smaller routing tables · fewer routing updates · faster convergence Hides internal network details · better scalability How it works The router advertises one aggregated prefix Longest Prefix Match always prefers the more specific route Traffic to […]
Route Redistribution — And Its Loop Traps
Route redistribution shares routes between different routing protocols – but introduces complexity and potential routing loops. It happens on a router running multiple protocols, which acts as the redistribution point, translating routes from one protocol’s metric to another’s. When is it used? Networks with multiple routing protocols Migration between protocols Joining administrative domains Facts (CCNA) […]
VRRP & GLBP
VRRP (open standard) and GLBP (Cisco, with load balancing) – the FHRP siblings of HSRP. VRRP facts Topic VRRP Standard Open standard (RFC 5798) Multicast 224.0.0.18 · IP protocol 112 Virtual IP / MAC 1 per group · 0000.5e00.01XX Roles Master / Backup Priority / Timers 100 (0–255) · Advertisement 1 s Versions VRRPv2 (IPv4), […]