BGP advertise-best-external on RR
Hi, I have a classic network design with 3 gateways, each receive a default route from different upstream provider. Each gateway has a BGP session with a route-reflector, which in turns reflects the best BGP route to the other PE routers in the network. The route-reflectors are running the SRE train (12.2(33)SRE1) and here exist the problem. I need to leak all the default routes (3 default routes) from the gateways into the PE routers. I have done this via bgp advertise-best-external on the gateways. So far, the default routes exist on the route-reflector, however it's suppressed as the RR will only send the best path. I have configured bgp advertise-best-external also on the RR but it didn't work, because the RR didn't see that the different default routes received are of "external" type. Cisco didn't state that clearly and it only stated that bgp best external feature won't work on the RR unless you get an ASR loaded with an IOS-XE 3.4 or later! Anyhow, do anyone here has a suggestion of how to get this done without replacing my RR sticking to this classical network design? Thanks. -- Mohamed Kamal Core Network Sr. Engineer
BGP Add-Path might be your friend . You can look at diverse-path as well . Sent from my iPhone
On Aug 24, 2015, at 2:07 PM, Mohamed Kamal <mkamal@noor.net> wrote:
Hi,
I have a classic network design with 3 gateways, each receive a default route from different upstream provider. Each gateway has a BGP session with a route-reflector, which in turns reflects the best BGP route to the other PE routers in the network. The route-reflectors are running the SRE train (12.2(33)SRE1) and here exist the problem.
I need to leak all the default routes (3 default routes) from the gateways into the PE routers. I have done this via bgp advertise-best-external on the gateways. So far, the default routes exist on the route-reflector, however it's suppressed as the RR will only send the best path.
I have configured bgp advertise-best-external also on the RR but it didn't work, because the RR didn't see that the different default routes received are of "external" type. Cisco didn't state that clearly and it only stated that bgp best external feature won't work on the RR unless you get an ASR loaded with an IOS-XE 3.4 or later!
Anyhow, do anyone here has a suggestion of how to get this done without replacing my RR sticking to this classical network design?
Thanks.
-- Mohamed Kamal Core Network Sr. Engineer
It's only supported on the 15.2(4)S and later not the SRE train. I might consider an upgrade. One more question regarding this, can you configure the RR to be the main and shadow RR? Mohamed Kamal Core Network Sr. Engineer On 8/24/2015 9:16 PM, Diptanshu Singh wrote:
BGP Add-Path might be your friend . You can look at diverse-path as well .
Yes . In the case of diverse path , shadow route reflector will be the one wherever you enable commands to trigger diverse path computation. Good thing with diverse path is that the RR-Clients don't have to have any support but bad thing is that it can only reflect One additional best-path( second best path ) . Sent from my iPhone
On Aug 24, 2015, at 2:31 PM, Mohamed Kamal <mkamal@noor.net> wrote:
It's only supported on the 15.2(4)S and later not the SRE train. I might consider an upgrade.
One more question regarding this, can you configure the RR to be the main and shadow RR?
Mohamed Kamal Core Network Sr. Engineer
On 8/24/2015 9:16 PM, Diptanshu Singh wrote: BGP Add-Path might be your friend . You can look at diverse-path as well .
Hi, In your case I¹d recommend to use diverse path, due to its simplicity and non disruptive deployment characteristics. As you know - diverse path requires additional BGP session per additional (second, next, etc) path, in most cases not a problem, however mileage might vary. To my memory, in Cisco land - it has only been implemented in IOS, not XR, please check. Cheers, Jeff -----Original Message----- From: Diptanshu Singh <diptanshu.singh@gmail.com> Date: Monday, August 24, 2015 at 10:53 PM To: Mohamed Kamal <mkamal@noor.net> Cc: "nanog@nanog.org" <nanog@nanog.org> Subject: Re: BGP advertise-best-external on RR
Yes . In the case of diverse path , shadow route reflector will be the one wherever you enable commands to trigger diverse path computation.
Good thing with diverse path is that the RR-Clients don't have to have any support but bad thing is that it can only reflect One additional best-path( second best path ) .
Sent from my iPhone
On Aug 24, 2015, at 2:31 PM, Mohamed Kamal <mkamal@noor.net> wrote:
It's only supported on the 15.2(4)S and later not the SRE train. I might consider an upgrade.
One more question regarding this, can you configure the RR to be the main and shadow RR?
Mohamed Kamal Core Network Sr. Engineer
On 8/24/2015 9:16 PM, Diptanshu Singh wrote: BGP Add-Path might be your friend . You can look at diverse-path as well .
Hi, Diverse-path will only send the second best path, and in my case I have three routes not two. In addition to that, every PE will have to peer with the RR via a second session (on the same RR, as I will not deploy a new standalone shadow RR) and this will increase the BGP sessions to the double. Add-path will have a network-wide IOS upgrade for this BGP capability to be supported which is not viable now. So, is there any other recommendation other than the internet VRF with different RDs solution? Regards, Mohamed Kamal Core Network Sr. Engineer On 8/25/2015 11:37 AM, Jeff Tantsura wrote:
Hi,
In your case I¹d recommend to use diverse path, due to its simplicity and non disruptive deployment characteristics. As you know - diverse path requires additional BGP session per additional (second, next, etc) path, in most cases not a problem, however mileage might vary.
To my memory, in Cisco land - it has only been implemented in IOS, not XR, please check.
Cheers, Jeff
-----Original Message----- From: Diptanshu Singh <diptanshu.singh@gmail.com> Date: Monday, August 24, 2015 at 10:53 PM To: Mohamed Kamal <mkamal@noor.net> Cc: "nanog@nanog.org" <nanog@nanog.org> Subject: Re: BGP advertise-best-external on RR
Yes . In the case of diverse path , shadow route reflector will be the one wherever you enable commands to trigger diverse path computation.
Good thing with diverse path is that the RR-Clients don't have to have any support but bad thing is that it can only reflect One additional best-path( second best path ) .
Sent from my iPhone
On Aug 24, 2015, at 2:31 PM, Mohamed Kamal <mkamal@noor.net> wrote:
It's only supported on the 15.2(4)S and later not the SRE train. I might consider an upgrade.
One more question regarding this, can you configure the RR to be the main and shadow RR?
Mohamed Kamal Core Network Sr. Engineer
On 8/24/2015 9:16 PM, Diptanshu Singh wrote: BGP Add-Path might be your friend . You can look at diverse-path as well .
There's no such thing as free lunch right :). If BGP Add-Path or Diverse-Path isn't option for you then as you mentioned Internet VRF with different RD is the third option but you have to understand the implications here as well around increase in % of memory. Another option could be to bypass the RR's and just fully mesh it. But if none of the above is an option, then you may have to do some unnatural act to solve it. On Tue, Sep 1, 2015 at 7:51 AM, Mohamed Kamal <mkamal@noor.net> wrote:
Hi,
Diverse-path will only send the second best path, and in my case I have three routes not two. In addition to that, every PE will have to peer with the RR via a second session (on the same RR, as I will not deploy a new standalone shadow RR) and this will increase the BGP sessions to the double.
Add-path will have a network-wide IOS upgrade for this BGP capability to be supported which is not viable now.
So, is there any other recommendation other than the internet VRF with different RDs solution?
Regards,
Mohamed Kamal Core Network Sr. Engineer
On 8/25/2015 11:37 AM, Jeff Tantsura wrote:
Hi,
In your case I¹d recommend to use diverse path, due to its simplicity and non disruptive deployment characteristics. As you know - diverse path requires additional BGP session per additional (second, next, etc) path, in most cases not a problem, however mileage might vary.
To my memory, in Cisco land - it has only been implemented in IOS, not XR, please check.
Cheers, Jeff
-----Original Message----- From: Diptanshu Singh <diptanshu.singh@gmail.com> Date: Monday, August 24, 2015 at 10:53 PM To: Mohamed Kamal <mkamal@noor.net> Cc: "nanog@nanog.org" <nanog@nanog.org> Subject: Re: BGP advertise-best-external on RR
Yes . In the case of diverse path , shadow route reflector will be the
one wherever you enable commands to trigger diverse path computation.
Good thing with diverse path is that the RR-Clients don't have to have any support but bad thing is that it can only reflect One additional best-path( second best path ) .
Sent from my iPhone
On Aug 24, 2015, at 2:31 PM, Mohamed Kamal <mkamal@noor.net> wrote:
It's only supported on the 15.2(4)S and later not the SRE train. I might consider an upgrade.
One more question regarding this, can you configure the RR to be the main and shadow RR?
Mohamed Kamal Core Network Sr. Engineer
On 8/24/2015 9:16 PM, Diptanshu Singh wrote:
BGP Add-Path might be your friend . You can look at diverse-path as well .
Not a suggestion, just trying to learn something here. Is there an advantage to use a route reflector in the described setup, which appears to involve only a small number of routers? I would think that full mesh would solve the problem and at the same time be easier since you do not have to maintain any route reflectors. With peer-group it is not a real bother to configure a handful of iBGP peers. Regards, Baldur
On 2/Sep/15 09:30, Baldur Norddahl wrote:
Not a suggestion, just trying to learn something here. Is there an advantage to use a route reflector in the described setup, which appears to involve only a small number of routers? I would think that full mesh would solve the problem and at the same time be easier since you do not have to maintain any route reflectors.
With peer-group it is not a real bother to configure a handful of iBGP peers.
I and a bunch of others have always recommended starting with a route reflector regardless of your network size. It makes growing much easier. Mark.
participants (6)
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Baldur Norddahl -
dip -
Diptanshu Singh
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Jeff Tantsura -
Mark Tinka -
Mohamed Kamal