Re: Best way to have redundancy announcing on separate routers

[Tom Beecher <beecher () beecher cc>]

I'm not saying I *would* do it, or you *should* do it, I'm just answering
the questions being asked. :)

On Thu, Jan 2, 2025 at 3:21 PM Christopher Morrow <morrowc.lists () gmail com>
wrote:

> On Thu, Jan 2, 2025 at 2:55 PM Tom Beecher <beecher () beecher cc> wrote:
> > Jean-
> >
> > Thanks. Many BGP implementations have the ability to do conditional
> advertisements, where you announce (or don't) a set of prefixes based on
> the presents (or absence) of other routes. I don't think quagga does
> natively, and not sure if VyOS has added that on.
> > Conceptually, you want to be doing "announce these prefixes from this
> router only if I don't see routes from the upstream on the other router".
> The 'safest' way is probably to just monitor default, but it depends on
> your environment.
> >
>
> That sort of thing seems like extra complexity, no?
> If the 2 internal routers have iBGP and you are fairly sure that you
> won't lose that path/view you should be able to just announce
> the same prefixes to both ISP peerings and possibly add some
> metric-equivalent data to distance one link vs the other, no?
> (common metric for this is the as-path, add your as N times, where N
> is <10 and > 2 probably?)
>
> how exact do you want your split here to be jfranco ? (is 'mostly
> everything over PRIMARY with some over SECONDARY' ok?)
>
> > On Fri, Dec 27, 2024 at 6:09 PM Jean Franco <jfranco () maila inf br>
> wrote:
> > > Hi Tom,
> > > This is exactly what I was planning.
> > > I'm announcing a block via ISP1 and another set of blocks via ISP2, and
> have iBGP running between them.
> > > Thanks a lot!!
> > >
> > > Best regards,
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > > On Fri, Dec 27, 2024 at 1:00 PM Tom Beecher <beecher () beecher cc> wrote:
> > > > Jean-
> > > >
> > > > Yeah, don't worry about people complaining.
> > > >
> > > > Is this an accurate description of what you are trying to achieve?
> > > >
> > > > - Have 2 different sets of prefixes that you announce. Set A via
> router1/ISP1 , Set B via router2/ISP2
> > > > - If BGP to one of your ISPs goes down, start announcing those
> prefixes to the other ISP. ( Example, if ISP2 goes down, start announcing
> prefix Set B over ISP1 )
> > > > On Thu, Dec 26, 2024 at 8:16 AM Jean Franco <jfranco () maila inf br>
> wrote:
> > > > > Hi guys,
> > > > > I've been on the list for as long as I cannot even remember.
> > > > > So just you know, I'm not new at this.
> > > > >
> > > > > This is no easy task, that's why I came here looking for help.
> > > > > I'm sorry if I brought anguish to the experts on the list!
> > > > > I thought I could bring something that someone may have experienced
> before.
> > > > > I haven't solved this yet, but at least I've received some valuable
> suggestions and I Thank you!
> > > > > About all the details of the connections, numbers of peerings, PNI's
> and IXP's I have left them out, since I figured this additional information
> could make things worse.
> > > > > ISP 1 <router01> ====20KM====<Router>====20KM====<router02> ISP2
> > > > >
> > > > > The ISP connections are all 10G.
> > > > > I don't believe these routers are DFZ capable.
> > > > > All the routers are well capable and already receive the full routes.
> > > > > The connections between these routers are 40G.
> > > > >
> > > > > Best regards,
> > > > >
> > > > >
> > > > > On Thu, Dec 26, 2024 at 12:53 AM Bryan Fields <Bryan () bryanfields net>
> wrote:
> > > > > > On 12/25/24 6:18 PM, Randy Bush wrote:
> > > > > > > where does one go for is-is help?  the mtu issie can be painful!!!
> > > > > >
> > > > > > I think here would be good too.  I recently had to do this between a
> Cisco
> > > > > > 3945e and a Juniper, and from my unrevised notes:
> > > > > >
> > > > > > vlan {
> > > > > >   unit 405 {
> > > > > >     family iso {
> > > > > >     # holy shit this is important.  CISCO and Juniper will not talk
> unless the
> > > > > > MTU is set
> > > > > >         mtu 1492;
> > > > > >       }
> > > > > >    }
> > > > > > }
> > > > > >
> > > > > > :-)
> > > > > >
> > > > > > --
> > > > > > Bryan Fields
> > > > > >
> > > > > > 727-409-1194 - Voice
> > > > > > http://bryanfields.net