[c-nsp] Connecting isolated L3 islands without GRE tunnels

Pshem Kowalczyk pshem.k at gmail.com
Thu Jul 11 17:11:53 EDT 2013


I'm also slightly confused by the requirements here. If all the sites
are publicly addressed, with internet access, why don't you just plain
route the traffic across the internet? Each site has a default route
from your provider and advertises its internal ranges to the provider.
All the other sites can see that as well, so a local 3560 either sends
it to the provider (for all remote sites, the provider does the
routing towards the end site) using default route, or keeps it
internal based on its local routing table. If you use the same AS in
all the 'islands' then 'allowas-in 1' on the BGP session with the
provider should do it.

kind regards

On 12 July 2013 07:49, Pavel Dimow <paveldimow at gmail.com> wrote:
> Hi Phil,
> the main problem is that I have 3560 at branch offices which I can not
> change. The 3560 have a very poor GRE tunnel performance (when it acts as
> endpoint). I have multiple branch offices (each with 3560) and one central
> office. I am wondering if there is any mechanism that I can use on 3560 to
> tunnel traffic from branch office to central location? Keep in mind that it
> is very expensive to have L2 or L3 VPN. I need to exchange routes between
> central and branch offices and my solution would be some BGP and few static
> routes for my super nets.
> My best guess is that I will need to change 3560 but I want to be sure that
> there is nothing else I can do with those boxes..
> On Thu, Jul 11, 2013 at 11:15 AM, Phil Mayers <p.mayers at imperial.ac.uk>wrote:
>> On 10/07/13 21:18, Pavel Dimow wrote:
>>> Hi,
>>> I have a a few branch offices and I want to connect them with central
>>> site.
>>> Now I have a few problems. First at every branch I have the same provider
>>> but it is very expensive to use any kind of their L2 or L3 MPLS services
>>> hence I have only internet access. Also, at every branch we have cisco
>>> 3560
>>> with very bad GRE tunnel performance (about 2Mbps).
>>> Now my only solution is to like this:
>>> Setup EBGP with ISP (require only default route)  and setup IBGP with
>>> route
>>> reflector at my central location. With this I should be able to have only
>>> default route from my ISP and all routes from my network (central and
>>> branch offices) and use only a single link from ISP without the need for
>>> GRE tunnel.
>>> Any ideas if I am missing something? Any advices for better solution?
>> I don't understand your solution. Without some kind of tunnel or
>> encapsulation, your routing table is irrelevant - once the traffic reaches
>> your ISP, it obeys their routing table, and will either be forwarded
>> correctly (in which case you don't need the iBGP) or incorrectly (in which
>> case iBGP does nothing)
>> Can you describe in more detail what you mean by "isolated L3 islands"?
>> I suspect you're going to need an additional or different box at each site
>> to encapsulate the traffic.
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