Mailing List Archive: only advertise network when internal IF is up?

only advertise network when internal IF is up?

Jan 9, 2017, 1:35 AM

Post #1 of 4 (673 views)

Hi,

In my setup I have two routers (lets say R1 and R2) connected to two
uplinks of one large ISP.

Both of my routers where advertising my prefix and the ISP sends return
packets to R1 and in failure of R1 switches to R2.

Lastly I had an issue with the internal NIC of R1, so iBGP addressed
outgoing packets via R2, but since the external NIC of R1 was
operational the router itself advertised the prefix and so return
packets from the ISP were send to nowhere on R1.

I'm using the network statement in BGP and in Zebra have a Null Route
for the prefix. My thought to solve this explicit issue is to set a
route for the prefix via internal IF, so when the NIC is down R1 doesn't
advertise any networks.

Not really sure if this is really the way how to solve situations like
these? I also read about bgp conditional advertisement, but perhaps this
is a bit oversized for a small network?

Any ideas? Or is a route via internal just fine?

Thanks,

Michael

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Re: only advertise network when internal IF is up? [ In reply to ]

m.muenz at spam-fetish

Jan 10, 2017, 2:03 PM

Post #2 of 4 (667 views)

Permalink

Am 09.01.2017 um 10:35 schrieb Muenz, Michael:
>
>
> I'm using the network statement in BGP and in Zebra have a Null Route
> for the prefix. My thought to solve this explicit issue is to set a
> route for the prefix via internal IF, so when the NIC is down R1
> doesn't advertise any networks.
>

Ok, this doesn't work, tested it, shut down eth1 and the network was
still advertised.
Also I got in a bit trouble, because not every network in the assigment
is in use, so it tries to find it on eth1 and I ended in full arp cache :)

> Not really sure if this is really the way how to solve situations like
> these? I also read about bgp conditional advertisement, but perhaps
> this is a bit oversized for a small network?
>
>
> Any ideas? Or is a route via internal just fine?

So I'm back at the beginning, any ideas how to solve this with quagga?

Thanks,
Michael

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Re: only advertise network when internal IF is up? [ In reply to ]

paul at ddproperty

Jan 13, 2017, 12:32 AM

Post #3 of 4 (665 views)

Permalink

This is usually done by originating your prefixes on the core router.

In your case, set up a BGP session with the router on the other side of
the link, and originate your prefix from there.

Core router <-- iBGP --> Border router <-- eBGP --> Peer router

On the core router you have `network x.x.x.x/x` in your configuration.
On the border router you don't have any `network` prefixes, just
advertise the prefixes you get from the core router to the peer.

When the link between the core and border router goes down, you will
stop advertising the prefixes to the peer (so the traffic will be routed
over a backup path).

On 2017-01-11 05:03, Muenz, Michael wrote:
> Am 09.01.2017 um 10:35 schrieb Muenz, Michael:
>>
>>
>> I'm using the network statement in BGP and in Zebra have a Null Route
>> for the prefix. My thought to solve this explicit issue is to set a
>> route for the prefix via internal IF, so when the NIC is down R1
>> doesn't advertise any networks.
>>
>
> Ok, this doesn't work, tested it, shut down eth1 and the network was
> still advertised.
> Also I got in a bit trouble, because not every network in the assigment
> is in use, so it tries to find it on eth1 and I ended in full arp cache :)
>
>> Not really sure if this is really the way how to solve situations like
>> these? I also read about bgp conditional advertisement, but perhaps
>> this is a bit oversized for a small network?
>>
>>
>> Any ideas? Or is a route via internal just fine?
>
> So I'm back at the beginning, any ideas how to solve this with quagga?
>
> Thanks,
> Michael
>
>

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Re: only advertise network when internal IF is up? [ In reply to ]

m.muenz at spam-fetish

Jan 15, 2017, 10:26 AM

Post #4 of 4 (663 views)

Permalink

Am 13.01.2017 um 09:32 schrieb Paul Tobias:
> This is usually done by originating your prefixes on the core router.
>
> In your case, set up a BGP session with the router on the other side of
> the link, and originate your prefix from there.
>
> Core router <-- iBGP --> Border router <-- eBGP --> Peer router
>
> On the core router you have `network x.x.x.x/x` in your configuration.
> On the border router you don't have any `network` prefixes, just
> advertise the prefixes you get from the core router to the peer.
>
> When the link between the core and border router goes down, you will
> stop advertising the prefixes to the peer (so the traffic will be routed
> over a backup path).
Hi Paul,

Thanks for your reply! I also thought about this, but I have 2 core
routers handling/advertising /22.
Is there a way to summarize on quagga to /20 for both core routers?

Thanks!

Michael

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