Routing Protocols

network design

distance vector vs link state


BGP is the ONLY real EGP (exterior gateway protocol) currently. Unlike all other routing protocols, BGP uses TCP as its transport protocol.

path vector protocol


The link-state approach, also known as the Dijkstras algorithm or as "shortest path first" (SPF).
"smarter" than distance vector protocols because they maintain a complex database of the network topology and status. This is accomplished using "link state advertisements" (LSA). LSAs are used to "map" out the network. The router uses this map to determine the shortest path for data destinations. The problem with this is that every time a configuration in the network changes, LSAs are broadcasted to and from all routers on the network. This causes a spike in router CPU usage, memory, and network bandwidth.


IS-IS : IS-IS is a link-state protocol supports both IPv4 and IPv6, typically only at ISP's these days
OSPF: link state protocol. v2 supports IPv4, v3 supports IPv6 only, not IPv4.


reduce mesh
approach 1) In network routing, BGP confederation is a method to use Border Gateway Protocol (BGP) to subdivide a single autonomous system (AS) into multiple internal sub-AS's, yet still advertise as a single AS to external peers. The intent is to reduce IBGP mesh size.
approach 2) A route reflector (RR) is a network routing component. It offers an alternative to the logical full-mesh requirement of internal border gateway protocol (IBGP). An RR acts as a focal point for IBGP sessions. The purpose of the RR is concentration. Multiple BGP routers can peer with a central point, the RR - acting as a route reflector server - rather than peer with every other router in a full mesh. All the other IBGP routers become route reflector clients.

IGRP and RIP :

Distance vector algorithms are also known as the Bellman-Ford algorithms. sends broadcasts of its routing table to neighboring devices. This is done quite often (the default is every 30 seconds). Distance Vector Protocols include IGRP and RIP.

You really won't want to use IGRP — it's the deprecated, older verson of Cisco's proprietary EIGRP (also proprietary).
EIGRP is reliable, fairly intuitive, and comparable in performance to OSPF, but runs only on Cisco equipment. It uses
hybrid approach. ie combination of distance vector and link state.


The Virtual Router Redundancy Protocol (VRRP) is a computer networking protocol that provides for automatic assignment of available Internet Protocol (IP) routers to participating hosts. This increases the availability and reliability of routing paths via automatic default gateway selections on an IP subnetwork.

The protocol achieves this by creation of virtual routers, which are an abstract representation of multiple routers, i.e. master and backup routers, acting as a group. The default gateway of a participating host is assigned to the virtual router instead of a physical router. If the physical router that is routing packets on behalf of the virtual router fails, another physical router is selected to automatically replace it. The physical router that is forwarding packets at any given time is called the master router.

VRRP is based on Cisco's proprietary Hot Standby Router Protocol (HSRP) concepts.

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