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I'm assuming the ASR only advertising 7k routes knows the other ASR already
has a better route to those prefixes based on what it is recieving from it.

As a test if you pull the uplink or do some pretending on import on ASR9K1
then ASR9K2 should advertise the full 90k on the ibgp session.

Matt




On Sun, 12 Mar 2023, 18:22 Mohammad Khalil via cisco-nsp, <
cisco-nsp@puck.nether.net> wrote:

> Greetings
> I have two ASR9K connected to different providers (Uplinks).
> I am receiving around 90K routes from each provider , as well , I have
> iBGP between the ASR9K.
> What am noticing is that ASR9K1 is advertising around 87K to ASR9K2 where
> ASR9Ks is advertising around 7K routes.
> Any hints?
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On 3/12/23 20:21, Mohammad Khalil via cisco-nsp wrote:

> Greetings
> I have two ASR9K connected to different providers (Uplinks).
> I am receiving around 90K routes from each provider , as well , I have iBGP between the ASR9K.
> What am noticing is that ASR9K1 is advertising around 87K to ASR9K2 where ASR9Ks is advertising around 7K routes.
> Any hints?

A case of active routes being announced to neighbors, where active
routes = best routes/paths as seen from each router's point of view.

ASR9K1 has more routes with better paths toward destinations via its
upstream than ASR9K2 does.

Mark.
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Thanks for the hint , actually this is what I have been thinking of but was wondering how can I get more details or samples about that as a matter of proof.
________________________________
From: cisco-nsp <cisco-nsp-bounces@puck.nether.net> on behalf of Mark Tinka via cisco-nsp <cisco-nsp@puck.nether.net>
Sent: Sunday, March 12, 2023 9:49 PM
To: cisco-nsp@puck.nether.net <cisco-nsp@puck.nether.net>
Subject: Re: [c-nsp] BGP Routes



On 3/12/23 20:21, Mohammad Khalil via cisco-nsp wrote:

> Greetings
> I have two ASR9K connected to different providers (Uplinks).
> I am receiving around 90K routes from each provider , as well , I have iBGP between the ASR9K.
> What am noticing is that ASR9K1 is advertising around 87K to ASR9K2 where ASR9Ks is advertising around 7K routes.
> Any hints?

A case of active routes being announced to neighbors, where active
routes = best routes/paths as seen from each router's point of view.

ASR9K1 has more routes with better paths toward destinations via its
upstream than ASR9K2 does.

Mark.
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On Sun, 12 Mar 2023 at 20:50, Mark Tinka via cisco-nsp
<cisco-nsp@puck.nether.net> wrote:

> ASR9K1 has more routes with better paths toward destinations via its
> upstream than ASR9K2 does.

Or at worst, race.

You might want add-path or best-external for predictability and
improved convergence time.

--
++ytti
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Hi,

On Sun, Mar 12, 2023 at 08:51:36PM +0200, Saku Ytti via cisco-nsp wrote:
> You might want add-path or best-external for predictability and
> improved convergence time.

Last time we did best-external with ASR9k it only worked in a useful
way if you are using labeled-unicast. That was many years ago, so
it might have been fixed, but "test and expect surprises".

In our case, the effect was that the local router that exported
best-external to its peers was also installing the best-external
path into its local FIB, as a load-shared path(!).

So we had packets come in from uplink, the "good" path was "send
internal over our network", but half the packets got balanced
via the "best-external" path. Intereresting isseus ensued.

To me this never made sense but TAC claimed "this is the way it is,
we're not considering this a bug, use labeled-unicast, then it will
work fine". As we didn't use LU, I could not verify this.

gert
--
"If was one thing all people took for granted, was conviction that if you
feed honest figures into a computer, honest figures come out. Never doubted
it myself till I met a computer with a sense of humor."
Robert A. Heinlein, The Moon is a Harsh Mistress

Gert Doering - Munich, Germany gert@greenie.muc.de

Thanks Saku and Gert for the kind replies , well received.
________________________________
From: cisco-nsp <cisco-nsp-bounces@puck.nether.net> on behalf of Gert Doering via cisco-nsp <cisco-nsp@puck.nether.net>
Sent: Sunday, March 12, 2023 9:58 PM
To: Saku Ytti <saku@ytti.fi>
Cc: cisco-nsp@puck.nether.net <cisco-nsp@puck.nether.net>
Subject: Re: [c-nsp] BGP Routes

Hi,

On Sun, Mar 12, 2023 at 08:51:36PM +0200, Saku Ytti via cisco-nsp wrote:
> You might want add-path or best-external for predictability and
> improved convergence time.

Last time we did best-external with ASR9k it only worked in a useful
way if you are using labeled-unicast. That was many years ago, so
it might have been fixed, but "test and expect surprises".

In our case, the effect was that the local router that exported
best-external to its peers was also installing the best-external
path into its local FIB, as a load-shared path(!).

So we had packets come in from uplink, the "good" path was "send
internal over our network", but half the packets got balanced
via the "best-external" path. Intereresting isseus ensued.

To me this never made sense but TAC claimed "this is the way it is,
we're not considering this a bug, use labeled-unicast, then it will
work fine". As we didn't use LU, I could not verify this.

gert
--
"If was one thing all people took for granted, was conviction that if you
feed honest figures into a computer, honest figures come out. Never doubted
it myself till I met a computer with a sense of humor."
Robert A. Heinlein, The Moon is a Harsh Mistress

Gert Doering - Munich, Germany gert@greenie.muc.de
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