Sunday, December 05, 2010

Routing protocols

Some stuff about static and dynamic routing protocols, and IP assignment to interfaces.

Directly connected:

When configuring an interface with an IP address that interface will become a host on that network (it will have it’s own ip address)

Before any static or dynamic routing is configured on a router, the router only knows about its own directly connected networks.

Also Connected is just like any other protocol (static or dynamic)

When configuring a static route with the exit interface of a router instead of a next-hop address it will show up as directly connected.

Static IP routes:

Can be added by an ICMP Redirect

Can be added by an administrator

Syntax is:

Router(config)#ip route prefix mask {ip-address | interface-type interface-number [ip-address]} [distance] [name] [permanent] [tag tag] 

The following parameters are used:
network-address - Destination network address of the remote network to be added to the routing table
subnet-mask - Subnet mask of the remote network to be added to the routing table. The subnet mask can be modified to summarize a group of networks.

One or both of the following parameters must also be used:
ip-address - Commonly referred to as the next-hop router's IP address
exit-interface - Outgoing interface that would be used in forwarding packets to the destination network

Dynamic routing protocols
  • RIP (Routing Information Protocol)
  • IGRP (Interior Gateway Routing Protocol)
  • EIGRP (Enhanced Interior Gateway Routing Protocol)
  • OSPF (Open Shortest Path First)
  • IS-IS (Intermediate System-to-Intermediate System)
  • BGP (Border Gateway Protocol)


  • classful, distance vector routing protocol.
  • does not include subnet mask in the route updates
  • RIP uses hop count for its metric
  • maximum 15 hops
  • metric of 16 hops == unreachable/infinite
  • encapsulated in a UDP segment
  • src/dest port 520
  • sent to ip address
  • full route table sent to neighbors every 30s (variation 0-15%)
  • enabled in global configuration mode via the command – router rip
  • The network command enables the interface to send and receive RIP updates and also advertises that network in RIP updates to other routers.
  • debug ip rip command can be used to view the RIP updates that are sent and received by the router.
  • passive-interface command is used to tell RIP that an interface should not be given RIP updates but participates in the Route Updates.
  • RIP entries are displayed in the routing table with the source code of R
  • Default routes are propagated in RIP by configuring a static default route and using the
    default-information originate command in RIP.

RIPv1 automatically summarizes subnets to their classful address when sending an update out an interface that is on a different major network than the subnetted address of the route. When a router receives a RIPv1 routing update, RIP must determine the subnet mask of that route. If the route belongs to the same major classful network as the update, RIPv1 applies the subnet mask of the receiving interface. If the route belongs to a different major classful network than the receiving interface, RIPv1 applies the default classful mask.

RIPv2 uses CIDR notation or classless addressing,VLSM, sends the subnet mask along with the update, support for discontinuous networks.
(c)#router rip
(c-router)#version 2
(c-router)#network [add directly connected networks]

By adding the directly connected networks and all routers supporting the protocol then all will receive the routing updates.



La rutarea statica:

Nu este nevoie de a introduce o adresa IP pe interfete serial, legaturile serial sunt oricum Point to Point.

Se poate introduce simplu doar interfata de iesire a router-ului.

Odata ce este pusa interfata de iesire in comanda show ip route orice retea remote va aparea ca si direct conectata.

In cazul retelelor multi acces recomandat este sa se introduca atat interfata de iesire a router-ului cat si IP-ul next-hop.

Protocoalele de rutare dinamice adauga automat asta.

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