OSPF,EIGRP,BGP

[rmv72]

Is't possible to describe typical situation when i must to use OPSF,EIGRP,BGP. I mean when i must prefer one protocol and when other?

[hbaerten · Accepted solution]

First of all, BGP is an EGP - External Gateway Protocol - while OSPF and EIGRP are IGPs (Internal GP).

So BGP is mainly used to connect your internetwork with an "external" entity (most often this will be another company, or an ISP) while OSPF and EIGRP (and others, e.g. IS-IS is popular for very large networks) are used for routing within an entity.

One possible deciding factor when choosing an IGP is the fact that EIGRP is Cisco proprietary so you won't be able to use it if you network includes non-Cisco devices.

OTOH, EIGRP supports routing of IPX and Appletalk as well as IP, where OSPF is IP-only.

There are many other factors to take into account though, like convergence time, scalability, memory and CPU usage, bandwidth usage, (unequal-cost) load balancing, design constraints, available knowledge etc.

Note that you can also use one IGP in one part of your network and another IGP in the other part, and redistribute routes between the IGP's.

E.g. we talk RIP with some older 3com routers and inject those routes into our OSPF backbone.

hth

Herbert

[ruwhite]

And don't forget IS-IS. :-)

I'll back Herbert up, and say it all just depends on what you're trying to do, and what the network looks like. I tend to like EIGRP for hub and spoke, and one of the link state protocols for more meshy environments--there are a lot of other rules of thumbs most network designers go by, not least of which is what they are familar with/have the most experience with. :-)

Russ.W