Running Private BGP on top of seperate EIGRP AS's in Corporate Enterprise

[gokada]

Need help w/designing network; our current environment has 1 single AS with all routers globally running EIGRP AS1. Proposal to run (exterior) BGP (private AS) on top of 6 regional (interior) EIGRP Autonymous-Systems, will improve network stability? Using 2 Class B networks not advertised to the internet, each region is summarized and w/in bit boundary....should I stay with EIGRP only ? Go to OSPF? Run BGP w/EIGRP? Need advice, don't really know BGP

[steve.barlow]

What is your primary concern? Sounds to me like stability is, if that is true look into summarizing routes, using stub routing and ip event dampening and the underlying cause of the instability.

Comparing OSPF and EIGRP, a lot of this has to do with personal preference and comfort level with either EIGRP or OSPF. Both will do the job well. EIGRP is easy to implement and takes less thought. Take that for what you want.

Now for the technical reasons:

-EIGRP is proprietary to cisco, OSPF is an IETF standard

-EIGRP scales well, takes less memory and CPU. Might be a consideration if running on low end routers.

-OSPF can scale slightly better in larger environments due to areas and based on implementers design.

-EIGRP has also better load balancing tweaks compared to OSPF

-both support secure transmition - message-digest key

-OSPF takes more knowledge to implement well (DR, areas, NBMA, LSAs)

-Both can summarize, EIGRP can anywhere on any interface

-Use different timers, which can be tweaked but that can lead to errors and troubleshooting.

Conclusion: both will do the job very well. But as you are already using EIGRP, I wouldn't change without very good reason. Avoid redistribution unless you have to. BGP is complex and if you don't really know it you may want to stay away. You wouldn't be the first or last company to run regional areas with EIGRP and the core on BGP. If you tweak EIGRP and you are still experiencing instability, only then would I look at changing. See prior discussions on this topic: http://forums.cisco.com/eforum/servlet/NetProf?page=netprof&CommCmd=MB%3Fcmd%3Ddisplay_location%26location%3D.ee89484/1

Keep it simply.

Hope it helps.

Steve

[bbranch]

It is common practice within the Enterprise to segregate your network up into several regional AS's to increase stability and scalability. Whether BGP is required is a debatable point, typically it is used if you wish to deploy any policy or traffic engineering as it has the better tools available for this.

If neither of these is a requirement you could just use several IGP AS's, this can, however, have a detrimental effect on the routers if they are attempting to do mutual redistribution between several IGP processes and administering the redistribution can be problematic. Additionally if you are using EIGRP, depending on where the aggregation of routes takes place, you may not increase the stability of the network as EIGRP Queries will still be propagated across AS boundaries (the original query will be terminated but a new one will be originated by the border router).

Personally I would recommend segregating the AS's with BGP.

[vcjones]

Expanding on Steve's and gokada's responses... BGP may be of benefit if either your network is REALLY large or you have specific routing policy requirements, neither of which is evident from your inital posting.

It is far more likely that what your network really needs is a cleanup of the addressing and address summarization so that routing can be hierarchical rather than flat. EIGRP networks have a nasty habit of growing in a very haphazard manner until no routing protocol could sort out the tangle. By the time you go through the organization required to support BGP, you may find that the addressing changes and hierarchical design that results could be easily supported in a single EIGRP AS, making the need to actually run BGP moot.

OSPF tends to scale better merely because the hierarchy enforced by the backbone area forces you to think in terms of routing hierarchy before the network gets large enough to make renumbering outrageously painful. If you only have a few hundred sites, look at what it would take to do a good OSPF design, selecting the appropriate backbone sites and summarizing routes at each area boundary. You can then apply the same design to your EIGRP network, without the pain of actually converting to OSPF. There is absolutely no need for routers in Singapore to be aware of the internal structure of your branch on the fourth floor of a building in London.

As for the benefits of OSPF versus EIGRP, either can work very well in a well designed network. OSPF gets the nod if your topology makes the availability of feasible successors a challenge between critical sites or you want to use routers from vendors other than Cisco. EIGRP gets the nod if your routers are short on CPU power or your traffic patterns are not conducive to dividing the network into areas as required by OSPF.

Good luck and have fun!

Vincent C Jones

http://www.networkingunlimited.com

[gokada]

Thank you All for your answers. They have been quite helpful and I will do a lot more planning with my peers to see where we should go. Your help is definately appreciated. - Gokada