CCNA Articles

Total available count: 11
Subject - Networking
Subsubject - CCNA

About EIGRP (Enhanced Interior Gateway Routing Protocol) and Access-Lists

EIGRP (Enhanced Interior Gateway Routing Protocol):

EIGRP is the only routing protocol in the world which supports backup routes; backup routes in the sense that every routing protocol creates a backup route when a specific route goes down, but in case of EIGRP, it remembers the backup routes. Remembering the backup routes is something known as the Topology Table, so whenever a link goes down EIGRP automatically shifts to the next best route to the destination. When compared with SPF algorithm of OSPF Diffused Update Algorithm (DUAL) of EIGRP does not put much pressure on the router.

Advantages of EIGRP over other routing protocols:

1. Backup routes (fast convergence/ DUAL)
2. Simple configuration
3. Flexibility in summarization
4. Unequal cost LOAD BALANCING
5. Combines best of Distance Vector and Link State
6. Supports multiple network protocols

Cisco created EIGRP because it wanted all features of Distance Vector and Link State Protocol minus the complexity of OSPF.

When compared with OSPF, Route summarization is held in the Area Border Routers only, but in case of EIGRP the concept of areas is absent and only because of this any router can do route summarization.

Unequal cost load balancing helps the routers send packets to their destination through the backup link also by combining bandwidth of both the links whereas the other routing protocols send packets through only one link even if there were more than one link to the destination.

EIGRP tables and terminology:

A router running EIGRP maintains three tables:
1. Neighbor Table
2. Topology Tables 
3. Routing Tables

Like OSPF, EIGRP also maintains a neighbor table, it also uses the Hello protocol to avail the neighbor table. When routes are created all the routes go to the topology table. If there are two routes to the same destination then the best routes goes into the topology table as the Successor i.e. the primary route and this route moves into the routing table; on the other hand the next mule which is the backup route will go into the topology table as the feasible successor. When the successor link goes down automatlcally the feasible successor moves into the routing lahle. EIGRP has the term which is called sub-second conversion which means that it can converge within seconds.


Access-lists: What they are ?

A list of permit and deny statements:-

> Permit
> Deny
> Permit TCP port 80 for 
> Permit all TCP traffic for

What they can be used for?

> Access control
> Quality of Service
> Demand Dial Routing
> Policy Routing
> Route Filtering

So we can define access control lists as the statements which identifies traffic to be allowed or denied to enter into a network in a way.

NAT can also be configured through access lists i.e. when using internet the private IP addresses would be translated to public IP addresses.

Moroever prioritising some traffic and deprioritising the others can be termed as QoS. So one a specific traffic may have the upper hand over the others when accessing is concerned.

Using ACL's for security:

> List is read from top to bottom and it stops at the first match
> Invisible implicit deny at the bottom
> ACL is applied to an interface inbound or outbound

Adding ACL capabilities:

1. Standard 
2. Extended 
3. Dynamic

Standard accets list:
The main features of standard access lists is as follows
1. It depends on the source IP address,i.e. in these kind of ACL a host is permitted or denied based on who you are, not really what you are accessing.
2. Only because of the above mentioned feature the router will have a better processing power.
3. An application will decide what type of affect would seen when the ACL is Implemented.

Extended access lists: 
Here are the features of extended ACL
1. It depends on a detailed path would have to give every details starting from source, destination, protocol, port number, operator etc.
2. Hence the router must have a better processor to handle these kinds ACL's.