This is a really complicated question, and a full answer
is beyond the scope of this document. Here are the beginnings
of an answer.

Note that Hello is no longer shipped with cisco routers, and that EGP has been
declared Historical (and thus obsolete) by the IETF. Don't use them.


Protocol        RIP     HELLO  IGRP   OSPF    EIGRP  IS-IS  EGP     BGP4
--------------------------------------------------------------------------
Type            IGP     IGP    IGP    IGP     IGP    IGP    EGP     EGP
Algorithm       DV      DV     DV     SPF     DUAL   SPF    DV      PV
Metrics         Hopcnt  Delay  Speed  Arb.    Speed  Arb.   Policy  Policy
Convergence     Slow    Unstb  Mdt    Fast    Fast   Fast   Slow    Fast
Standard?       IETF    No     No     IETF    No     ISO    Hist.   IETF
Complexity      Simple  Simple Simple Complx  Complx Complx Simple  Complx
Multipath?      Yes     Yes    Yes    Yes     Yes    Yes    Yes     [*]
Var-netmask?    No      No     No     Yes     Yes    Yes    No      YES

Notes
-----

IGP = interior gateway protocol, used to build routing tables within an AS.
EGP = exterior gateway protocol, used to communicate reachability
information between AS's.


Algorithms
----------
DUAL = DV with diffusing update algorithm (Garcia-Luna-Aceves et al)
DV   = Distance Vector (Bellman-Ford)
PV   = "Path Vector"
SPF   = Shortest-path-first (Dijkstra)

Metrics
-------

A metric is how the protocol measures the network to determine the
"best" path.

"Speed" refers typically to link speed, not available bandwidth.
"Arb." indicates that the metrics are arbitrary and configurable.

HELLO tried to use available bandwidth by monitoring round-trip delay,
but was not generally successful at this.

Metrics are not directly exchangable when redistributing routing
information from one protocol to another. IGRP and EIGRP use
compatible and automatically convertable metrics.

Convergence
-----------

Qualitatively, convergence measures how fast routers using this
protocol will adapt to changes in the topology of the network.

"Unstb" indicates a protocol which in general never decided on a
stable configuration but continually oscillated between alternatives.

Complexity
----------

An observation of how complex the protocol is to implement.

Multipath
---------

Multipath indicates whether the protocol support and transport
multiple equal- or different- cost pathways across between endpoints?

[*] indicates that BGP4 supports multipath for IBGP (Internal BGP, a
full mesh of all border routers within an AS), but not for EBGP
(External BGP).

Variable netmask (Var-netmask)
------------------------------

Indicates whether the protocol allows for and transports different
masks for the subnets of a routed network.