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Variable Length Subnet Mask: neighbour subnets are allowed to be different sizes, see VLSM.htm : maximises address space  
classfull: comms must remain withing the same subnet:   route aggregation: the use of a lowest common denominator
classless: comms can be between similar subnets: RIPv2, EIGRP, OSPF, ISIS address to represent a group of addresses.  
ip subnet zero:  the lowest and highest sub-subnets within the subnet can be used for host addresses despite the fact that network or broadcast
that network or broadcast addresses exist in that subnet: classless routing protocol required.      
no ip subnet zero: network or broadcast addresses exist in that subnet and preclude use of host addresses: waste of address space occurs.
dynamic routes: learnt from other routers  
static routes: manually set: sends defined addresses to a next hop router  
default routes: manually set: sends all 0.0.0.0 0.0.0.0 addresses to a last hop router
RIPv1: classfull, interior gateway protocol i.e. within an AS (autonomous system), simple, distance vector, broadcasts entire routing table every
 30 secs on 255.255.255.255, metric = hop count, 15 max hops, uses split horizon, 4 (or 6) equal cost paths, no authentication, no subnet mask info.
RIPv2: classless, interior gateway protocol i.e. within an AS (autonomous system), simple, distance vector, multicasts entire routing table every
 30 secs on 224.0.0.9, metric = hop count, 15 max hops, uses split horizon, 4 (or 6) equal cost paths, MD5 authentication, includes subnet mask info.
router(config)# router rip  
router(config-router)# version2  
router(config-router)# network xxx.xxx.xxx.xxx              
IGRP: classfull, interior gateway protocol i.e. within an AS (autonomous system), scaleable, hybrid distance vector / link state, broadcasts pdu's,
metric = bandwidth + delay, max 255 hops, cannot tag other protocol's routes.  
EIGRP: classless, interior gateway protocol i.e. within an AS (autonomous system), scaleable, hybrid distance vector / link state, broadcasts pdu's
metric = bandwidth + delay, max 224 hops, tags other protocol's routes as E=external, tag num. 0 - 255. Can replace other protocols, eg Novell RIP.
maintains neighbour, topology and routing table, uses distance vector to calculate routes and link state to update neighbours and send routing information.
multicasts/unicasts on 224.0.0.10, sends hello packets every 5 secs to discover neighbours, sends acknowledgement to hello's, sends updates to new
neighbours or if topology change, sends queries if has no routes, sends relies to queries. uses RTP (reliable transport protocol), does not use TCP/IP.
successor route: the 4 best routes to a destination feasibilty successor route:   backup routes kept in the the topology table  
passive: a successor route in use active: a route being calculated  
router(config)# router eigrp <as num>  
router(config-router)# network xxx.xxx.xxx.xxx  
router(config-router)# eigrp log-neighbor-changes  
router(config-if)# bandwidth <kpbs>  
router(config-if)# ip summary-address eigrp <as num><xxx.xxx.xxx.xxx><yyy.yyy.yyy.yyy><admin dist>      
Router#show ip protocols      - Enables you to view the IP routing protocol configuration on the router.
Router#show ip route      - Shows detailed information about the networks the router is aware and the preferred paths to those networks.
     - Also gives the next logical hop as the next step in the path.