Which to use GRE tunnel,static routes or something else ?

Answered Question
Apr 9th, 2010

At present I have a network consisting of Edge routers C and D being connected to the Internet via Routers A and B

the default route for users attached to Router C is via Router A and the default route for users attached to Router D is via Router B

The EIGRP ensures their is always a default route available if a primary connection fails.

It has now been decided to host services outside the Corporate zone, but using the Corporate address space on Router E. Our service provider

has agreed to install static routes on Router A and Router B pointing to 172.16.48.0/22 so the outside world is properly directed,

My problem is that I want 172.16.48.0/22 to be part of EIGRP 1 and appear in the routing tables so it can be redistributed into EIGRP 2

but if the primary connection between Router C and Router A  fails I still want 172.16.48.0/22 to be visible to users in EIGRP 2 area

I have included a drawing Layout1.pdf


what are my options ?

with thanks G

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Correct Answer by Lei Tian about 6 years 8 months ago

Hi,

Multiple eigrp AS is not recommended. Because multiple eigrp AS will require mutual redistribution and that can cause potential loop. Besides, using multiple AS cannot stop query anyway. A single EIGRP AS with summarization is the best practice.

With proper configuration, GRE should work as well. However GRE usually add some other problem because of the MTU or high CPU, so I would not use GRE if there is other solution.

HTH,

Lei Tian

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Lei Tian Sat, 04/10/2010 - 19:21

Hi g.peart,

I prefer static route.

Have a static route on Router C for network 172.16.48.0/22 next hop point to Router A with track option, so that static route will be removed when link fails between Router C and Router A. Advertise this route into EIGRP on Rouer C.

On Router D configure a static route for network 172.16.48/0/22 next hop point to Router B with AD higher than 170, so this route will be less preferred than EIGRP route. Advertise this route into EIGRP on Router D.

One question, why do you use 2 EIGRP AS?

HTH,

Lei Tian

g.peart Sun, 04/11/2010 - 04:26

Thanks, that looks the way to go and probably a lot more stable then GRE tunnels (would GRE tunnels even work ?) I'll test build and see.

As for the EIGRP bit that was going to be another issue, but here goes anyway, Router D is actually

part of a RIP network that I am going to convert to EIGRP via the big bang approach,.( rewrite the start-up configs

on all the RIP routers, then reload and wait for convergence)

The drawing shows layout  after conversion, I was going to make all the routers that were in 172.17.0.0/16 part

of EIGRP 2 area, so Router D which is the only EIGRP speaking router at present  in 172.17.0.0/16  will become

part of EIGRP 2, I didn't want to introduce instability into 172.16.0.0/16 if it goes wrong so kept seperate  EIGRP AS,

would good practice dedicate all the corporate space as one EIGRP AS ?

Correct Answer
Lei Tian Mon, 04/12/2010 - 06:15

Hi,

Multiple eigrp AS is not recommended. Because multiple eigrp AS will require mutual redistribution and that can cause potential loop. Besides, using multiple AS cannot stop query anyway. A single EIGRP AS with summarization is the best practice.

With proper configuration, GRE should work as well. However GRE usually add some other problem because of the MTU or high CPU, so I would not use GRE if there is other solution.

HTH,

Lei Tian

g.peart Mon, 04/12/2010 - 07:27

Thank you for the advice, I'll amend my design as necessary

and go with a single EIGRP area, along with the floating static routes.

If I have time I'll test build using GRE tunnels as well, just to see what would happen.

regards

G Peart

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